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  • 1.
    Acero, F.
    et al.
    CEA Saclay, France.
    Aloisio, R.
    Osserv Astrofis Arcetri, Italy ; Univ Aquila, Dipartimento Sci Fis & Chim, INFN, Via Vetoio 1, I-67100 Laquila, Italy.;Gran Sasso Sci Inst, Italy.
    Amans, J.
    Observ Paris, France.
    Amato, E.
    Osserv Astrofis Arcetri, Italy.
    Antonelli, L. A.
    Osserv Astron Roma, Italy.
    Aramo, C.
    Ist Nazl Fis Nucl, Italy.
    Armstrong, T.
    Univ Durham, UK.
    Arqueros, F.
    Univ Complutense Madrid, Spain.
    Asano, K.
    Univ Tokyo, Japan.
    Ashley, M.
    Univ New South Wales, Australia.
    Backes, M.
    Univ Namibia, Namibia.
    Balazs, C.
    Monash Univ, Australia.
    Balzer, A.
    Univ Amsterdam, Netherlands.
    Bamba, A.
    Univ Tokyo, Japan.
    Barkov, M.
    RIKEN, Inst Phys & Chem Res, 2-1 Hirosawa, Wako, Saitama 3510198, Japan..
    Barrio, J. A.
    Univ Complutense Madrid, Grp Altas Energias, Av Complutense S-N, E-28040 Madrid, Spain..
    Benbow, W.
    Harvard Smithsonian Ctr Astrophys, 60 Garden St, Cambridge, MA 02180 USA..
    Bernloehr, K.
    Max Planck Inst Kernphys, Saupfercheckweg 1, D-69117 Heidelberg, Germany..
    Beshley, V.
    Inst Appl Problems Mech & Math, 3B Naukova St, UA-79060 Lvov, Ukraine..
    Bigongiari, C.
    Osserv Astron Torino, INAF, Corso Fiume 4, I-10133 Turin, Italy..
    Biland, A.
    Swiss Fed Inst Technol, Inst Particle Phys, Schafmattstr 20, CH-8093 Zurich, Switzerland..
    Bilinsky, A.
    Ivan Franko Natl Univ Lviv, Astron Observ, 1 Univ Ska St, UA-79000 City Of Lviv, Ukraine..
    Bissaldi, E.
    Politecn Bari, Bari, Italy.;INFN Bari, Bari, Italy..
    Biteau, J.
    Univ Paris 11, IPNO, IN2P3, CNRS, 15 Rue Georges Clemenceau, F-91406 Orsay, France.;Univ Paris 11, UMR 8608, 15 Rue Georges Clemenceau, F-91406 Orsay, France..
    Blanch, O.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
    Blasi, P.
    Osserv Astrofis Arcetri, Largo E Fermi 5, I-50125 Florence, Italy..
    Blazek, J.
    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
    Boisson, C.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
    Bonanno, G.
    INAF Osservatorio Astrofis Catania, Via S Sofia 78, I-95123 Catania, Italy..
    Bonardi, A.
    Radboud Univ Nijmegen, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Bonavolonta, C.
    Ist Nazl Fis Nucl, Sez Napoli, Via Cintia,Ed G, I-80126 Naples, Italy..
    Bonnoli, G.
    INAF Osservatorio Astron Brera, Via Brera 28, I-20121 Milan, Italy..
    Braiding, C.
    Univ New South Wales, Sch Phys, Sydney, NSW 2052, Australia..
    Brau-Nogue, S.
    IRAP, 9 Ave Colonel Roche,BP 44346, F-31028 Toulouse 4, France..
    Bregeon, J.
    Univ Montpellier, CNRS, IN2P3, Lab Univers & Particules Montpellier, CC 72,Pl Eugene Bataillon, F-34095 Montpellier 5, France..
    Brown, A. M.
    Univ Durham, Dept Phys, South Rd, Durham DH1 3LE, England.;Univ Durham, Ctr Adv Instrumentat, South Rd, Durham DH1 3LE, England..
    Bugaev, V.
    Washington Univ, Dept Phys, St Louis, MO 63130 USA..
    Bulgarelli, A.
    Ist Astrofis Spaziale & Fis Cosm Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Bulik, T.
    Univ Warsaw, Fac Phys, Ul Hoza 69, PL-00681 Warsaw, Poland..
    Burton, M.
    Univ New South Wales, Sch Phys, Sydney, NSW 2052, Australia..
    Burtovoi, A.
    INAF Osservatorio Astron Padova, Vicolo Osservatorio 5, I-35122 Padua, Italy..
    Busetto, G.
    Univ Padua, Dipartimento Fis, Via Marzolo 8, I-35131 Padua, Italy..
    Bottcher, M.
    North West Univ, Ctr Space Res, Potchefstroom Campus, ZA-2531 Potchefstroom, South Africa..
    Cameron, R.
    Stanford Univ, Dept Phys, Kavli Inst Particle Astrophys & Cosmol, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Phys, SLAC Natl Accelerator Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Capalbi, M.
    INAF Ist Astrofis Spaziale & Fis Cosm Palermo, Via U La Malfa 153, I-90146 Palermo, Italy..
    Caproni, A.
    UCS, NAT, Rua Galvao Bueno 8687,Bloco B,Sala 16, BR-01506000 Sao Paulo, Brazil..
    Caraveo, P.
    Ist Astrofis Spaziale & Fis Cosm, Via Bassini 15, I-20133 Milan, Italy..
    Carosi, R.
    Ist Nazl Fis Nucl, Sez Pisa, Largo Pontecorvo 3, I-56127 Pisa, Italy..
    Cascone, E.
    INAF Osservatorio Astron Brera, Via Brera 28, I-20121 Milan, Italy..
    Cerruti, M.
    Harvard Smithsonian Ctr Astrophys, 60 Garden St, Cambridge, MA 02180 USA..
    Chaty, S.
    CEA Saclay, CEA, IRFU, SAp, Bat 709, F-91191 Gif Sur Yvette, France..
    Chen, A.
    Univ Witwatersrand, 1 Jan Smuts Ave, ZA-2000 Johannesburg, South Africa..
    Chen, X.
    Pontificia Univ Catolica Chile, Avda Libertador Bernardo OHiggins 340, Santiago, Chile..
    Chernyakova, M.
    Dublin City Univ, Dublin 9, Ireland..
    Chikawa, M.
    Kindai Univ, Dept Phys, Higashiosaka, Osaka 5778502, Japan..
    Chudoba, J.
    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
    Cohen-Tanugi, J.
    Univ Montpellier, CNRS, IN2P3, Lab Univers & Particules Montpellier, CC 72,Pl Eugene Bataillon, F-34095 Montpellier 5, France..
    Colafrancesco, S.
    Univ Witwatersrand, 1 Jan Smuts Ave, ZA-2000 Johannesburg, South Africa..
    Conforti, V.
    Ist Astrofis Spaziale & Fis Cosm Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Contreras, J. L.
    Univ Complutense Madrid, Grp Altas Energias, Av Complutense S-N, E-28040 Madrid, Spain..
    Costa, A.
    INAF Osservatorio Astrofis Catania, Via S Sofia 78, I-95123 Catania, Italy..
    Cotter, G.
    Univ Oxford, Dept Phys, 1 Keble Rd, Oxford OX1 3NP, England..
    Covino, S.
    INAF Osservatorio Astron Brera, Via Brera 28, I-20121 Milan, Italy..
    Covone, G.
    Ist Nazl Fis Nucl, Sez Napoli, Via Cintia,Ed G, I-80126 Naples, Italy..
    Cumani, P.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
    Cusumano, G.
    INAF Ist Astrofis Spaziale & Fis Cosm Palermo, Via U La Malfa 153, I-90146 Palermo, Italy..
    D'Ammando, F.
    INAF IRA, INAF, Ist Radioastron, Via Gobetti 101, Bologna, Italy..
    D'Urso, D.
    INFN, Sez Perugia, Via A Pascoli, I-06123 Perugia, Italy..
    Daniel, M.
    Harvard Smithsonian Ctr Astrophys, 60 Garden St, Cambridge, MA 02180 USA..
    Dazzi, F.
    Cherenkov Telescope Array Observ, Saupfercheckweg 1, D-69117 Heidelberg, Germany..
    De Angelis, A.
    Univ Padua, Dipartimento Fis, Via Marzolo 8, I-35131 Padua, Italy..
    De Cesare, G.
    Ist Astrofis Spaziale & Fis Cosm Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    De Franco, A.
    Univ Oxford, Dept Phys, 1 Keble Rd, Oxford OX1 3NP, England..
    De Frondat, F.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
    Dal Pino, E. M. de Gouveia
    Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, R Matao 1226, BR-05508090 Sao Paulo, Brazil..
    De Lisio, C.
    Ist Nazl Fis Nucl, Sez Napoli, Via Cintia,Ed G, I-80126 Naples, Italy..
    Lopez, R. de los Reyes
    Max Planck Inst Kernphys, Saupfercheckweg 1, D-69117 Heidelberg, Germany..
    De Lotto, B.
    Univ Udine, Via Sci 208, I-33100 Udine, Italy.;INFN, Sez Trieste, Via Sci 208, I-33100 Udine, Italy..
    de Naurois, M.
    Ecole Polytech, CNRS, UMR 7638, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    De Palma, F.
    INFN, Sez Bari, Via Orabona 4, I-70126 Bari, Italy..
    Del Santo, M.
    INAF Ist Astrofis Spaziale & Fis Cosm Palermo, Via U La Malfa 153, I-90146 Palermo, Italy..
    Delgado, C.
    CIEMAT, Avda Complutense 40, E-28040 Madrid, Spain..
    della Volpe, D.
    Univ Geneva, Dept Phys Nucl & Corpusculaire, 24 Rue Gen Dufour, CH-1211 Geneva 4, Switzerland..
    Di Girolamo, T.
    Ist Nazl Fis Nucl, Sez Napoli, Via Cintia,Ed G, I-80126 Naples, Italy..
    Di Giulio, C.
    INFN, Sez Roma Tor Vergata, Via Ric Sci 1, I-00133 Rome, Italy..
    Di Pierro, F.
    Ist Nazl Fis Nucl, Sez Torino, Via P Giuria 1, I-10125 Turin, Italy..
    Di Venere, L.
    Univ Bari, Bari, Italy.;INFN Bari, Bari, Italy..
    Doro, M.
    Univ Padua, Dipartimento Fis, Via Marzolo 8, I-35131 Padua, Italy..
    Dournaux, J.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
    Dumas, D.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
    Dwarkadas, V.
    Univ Chicago, Enrico Fermi Inst, 5640 South Ellis Ave, Chicago, IL 60637 USA..
    Diaz, C.
    CIEMAT, Avda Complutense 40, E-28040 Madrid, Spain..
    Ebr, J.
    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
    Egberts, K.
    Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Golm, Germany..
    Einecke, S.
    TU Dortmund Univ, Dept Phys, Otto Hahn Str 4, D-44221 Dortmund, Germany..
    Elsaesser, D.
    Univ Wurzburg, Inst Theoret Phys & Astrophys, Campus Hubland Nord,Emil Fischer Str 31, D-97074 Wurzburg, Germany..
    Eschbach, S.
    Univ Erlangen Nurnberg, Inst Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Falceta-Goncalves, D.
    Univ Sao Paulo, Escola Arles Ciencias & Humanidades, Rua Arlindo Bettio 1000, BR-03828000 Sao Paulo, Brazil..
    Fasola, G.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
    Fedorova, E.
    Taras Shevchenko Natl Univ Kyiv, Astron Observ, 60 Volodymyrska St, UA-01033 Kiev, Ukraine..
    Fernandez-Barral, A.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
    Ferrand, G.
    RIKEN, Inst Phys & Chem Res, 2-1 Hirosawa, Wako, Saitama 3510198, Japan..
    Fesquet, M.
    CEA Saclay, CEA, IRFU, SEDI, Bat 141, F-91191 Gif Sur Yvette, France..
    Fiandrini, E.
    INFN, Sez Perugia, Via A Pascoli, I-06123 Perugia, Italy..
    Fiasson, A.
    Univ Savoie, CNRS, IN2P3, Lab Annecy le Vieux Phys Particules, 9 Chemin Bellevue BP 110, F-74941 Annecy Le Vieux, France..
    Filipovic, M. D.
    Western Sydney Univ, Locked Bag 1797, Penrith, NSW 2751, Australia..
    Fioretti, V.
    Ist Astrofis Spaziale & Fis Cosm Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Font, L.
    Univ Autonoma Barcelona, Dept Fis, Unitat Fis Radiac, E-08193 Bellaterra, Spain.;Univ Autonoma Barcelona, CERES IEEC, E-08193 Bellaterra, Spain.;Edifici Cc,Campus UAB, E-08193 Bellaterra, Spain..
    Fontaine, G.
    Ecole Polytech, CNRS, UMR 7638, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Franco, F. J.
    Univ Complutense Madrid, Grp Elect, Ave Complutense S-N, E-28040 Madrid, Spain..
    Freixas Coromina, L.
    CIEMAT, Avda Complutense 40, E-28040 Madrid, Spain..
    Fujita, Y.
    Osaka Univ, Grad Sch Sci, Dept Earth & Space Sci, Toyonaka, Osaka 5600043, Japan..
    Fukui, Y.
    Nagoya Univ, Dept Phys & Astrophys, Chikusa Ku, Nagoya, Aichi 4648602, Japan..
    Funk, S.
    Univ Erlangen Nurnberg, Inst Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Forster, A.
    Max Planck Inst Kernphys, Saupfercheckweg 1, D-69117 Heidelberg, Germany..
    Gadola, A.
    Univ Zurich, Inst Phys, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Lopez, R. Garcia
    Inst Astrofis Canarias, Via Lactea, E-38205 Tenerife, Spain..
    Garczarczyk, M.
    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
    Giglietto, N.
    Politecn Bari, Bari, Italy.;INFN Bari, Bari, Italy..
    Giordano, F.
    Univ Bari, Bari, Italy.;INFN Bari, Bari, Italy..
    Giuliani, A.
    Ist Astrofis Spaziale & Fis Cosm, Via Bassini 15, I-20133 Milan, Italy..
    Glicenstein, J.
    CEA Saclay, CEA, IRFU, SPP, Bat 141, F-91191 Gif Sur Yvette, France..
    Gnatyk, R.
    Taras Shevchenko Natl Univ Kyiv, Astron Observ, 60 Volodymyrska St, UA-01033 Kiev, Ukraine..
    Goldoni, P.
    Univ Paris Diderot, APC, CNRS IN2P3, CEA Irfu,Obs Paris,Sorbonne Paris Cite, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France..
    Grabarczyk, T.
    Acad Comp Ctr CYFRONET AGH, Ul Nawojki 11, PL-30950 Krakow, Poland..
    Graciani, R.
    Univ Barcelona, Inst Ciencies Cosmos, IEEC UB, Dept Fis Quant & Astrofis, Marti & Franques 1, E-08028 Barcelona, Spain..
    Graham, J.
    Univ Durham, Dept Phys, South Rd, Durham DH1 3LE, England.;Univ Durham, Ctr Adv Instrumentat, South Rd, Durham DH1 3LE, England..
    Grandi, P.
    Ist Astrofis Spaziale & Fis Cosm Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Granot, J.
    Open Univ Israel, Dept Nat Sci, 1 Univ Rd,POB 808, IL-43537 Raanana, Israel..
    Green, A. J.
    Univ Sydney, Sch Phys, Sydney Inst Astron, Sydney, NSW 2006, Australia..
    Griffiths, S.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
    Gunji, S.
    Yamagata Univ, Dept Phys, Yamagata, Yamagata 9908560, Japan..
    Hakobyan, H.
    Univ Tecn Federico Santa Maria, Ave Espana 1680, Valparaiso, Chile..
    Hara, S.
    Yamanashi Gakuin Univ, Fac Management Informat, Kofu, Yamanashi 4008575, Japan..
    Hassan, T.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
    Hayashida, M.
    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan..
    Heller, M.
    Univ Geneva, Dept Phys Nucl & Corpusculaire, 24 Rue Gen Dufour, CH-1211 Geneva 4, Switzerland..
    Helo, J. C.
    Univ Tecn Federico Santa Maria, Ave Espana 1680, Valparaiso, Chile..
    Hinton, J.
    Max Planck Inst Kernphys, Saupfercheckweg 1, D-69117 Heidelberg, Germany..
    Hnatyk, B.
    Taras Shevchenko Natl Univ Kyiv, Astron Observ, 60 Volodymyrska St, UA-01033 Kiev, Ukraine..
    Huet, J.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
    Huetten, M.
    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
    Humensky, T. B.
    Columbia Univ, Dept Phys, 538 West 120th St, New York, NY 10027 USA..
    Hussein, M.
    Univ Manitoba, 540 Machray Hall, Winnipeg, MB R3T 2N2, Canada..
    Horandel, J.
    Radboud Univ Nijmegen, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Ikeno, Y.
    Tokai Univ, Dept Phys, 4-1-1 Kita Kaname, Hiratsuka, Kanagawa 2591292, Japan..
    Inada, T.
    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan..
    Inome, Y.
    Konan Univ, Dept Phys, Kobe, Hyogo 6588501, Japan..
    Inoue, S.
    RIKEN, Inst Phys & Chem Res, 2-1 Hirosawa, Wako, Saitama 3510198, Japan..
    Inoue, T.
    Natl Astron Observ Japan, Div Theoret Astron, Osawa 2-21-1, Mitaka, Tokyo 1818588, Japan..
    Inoue, Y.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Chuo Ku, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 2525210, Japan..
    Ioka, K.
    Kyoto Univ, Yukawa Inst Theoret Phys, Kyoto 6068502, Japan..
    Iori, M.
    INFN, Sez Roma La Sapienza, Ple Aldo Moro 2, I-00185 Rome, Italy..
    Jacquemier, J.
    Univ Savoie, CNRS, IN2P3, Lab Annecy le Vieux Phys Particules, 9 Chemin Bellevue BP 110, F-74941 Annecy Le Vieux, France..
    Janecek, P.
    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
    Jankowsky, D.
    Univ Erlangen Nurnberg, Inst Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Jung, I.
    Univ Erlangen Nurnberg, Inst Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Kaaret, P.
    Univ Iowa, Dept Phys & Astron, Van Allen Hall, Iowa City, IA 52242 USA..
    Katagiri, H.
    Ibaraki Univ, Fac Sci, Mito, Ibaraki 3108512, Japan..
    Kimeswenger, S.
    Univ Catolica Norte, Ave Angamos 0610, Antofagasta, Chile..
    Kimura, S.
    Tokai Univ, Dept Phys, 4-1-1 Kita Kaname, Hiratsuka, Kanagawa 2591292, Japan..
    Knodlseder, J.
    IRAP, 9 Ave Colonel Roche,BP 44346, F-31028 Toulouse 4, France..
    Koch, B.
    Pontificia Univ Catolica Chile, Avda Libertador Bernardo OHiggins 340, Santiago, Chile..
    Kocot, J.
    Acad Comp Ctr CYFRONET AGH, Ul Nawojki 11, PL-30950 Krakow, Poland..
    Kohri, K.
    KEK High Energy Accelerator Org, Inst Particle & Nucl Studies, 1-1 Oho, Tsukuba, Ibaraki 3050801, Japan..
    Komin, N.
    Univ Witwatersrand, 1 Jan Smuts Ave, ZA-2000 Johannesburg, South Africa..
    Konno, Y.
    Kyoto Univ, Grad Sch Sci, Div Phys & Astron, Sakyo Ku, Kyoto 6068502, Japan..
    Kosack, K.
    CEA Saclay, CEA, IRFU, SAp, Bat 709, F-91191 Gif Sur Yvette, France..
    Koyama, S.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Chuo Ku, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 2525210, Japan..
    Kraus, M.
    Univ Erlangen Nurnberg, Inst Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Kubo, H.
    Kyoto Univ, Grad Sch Sci, Div Phys & Astron, Sakyo Ku, Kyoto 6068502, Japan..
    Mezek, G. Kukec
    Univ Nova Gorica, Lab Astroparticle Phys, Vipayska 13, Nova Gorica 5000, Slovenia..
    Kushida, J.
    Tokai Univ, Dept Phys, 4-1-1 Kita Kaname, Hiratsuka, Kanagawa 2591292, Japan..
    La Palombara, N.
    Ist Astrofis Spaziale & Fis Cosm, Via Bassini 15, I-20133 Milan, Italy..
    Lalik, K.
    Polish Acad Sci, Henryk Niewodniczanski Inst Nucl Phys, Ul Radzikowskiego 152, PL-31342 Krakow, Poland..
    Lamanna, G.
    Univ Savoie, CNRS, IN2P3, Lab Annecy le Vieux Phys Particules, 9 Chemin Bellevue BP 110, F-74941 Annecy Le Vieux, France..
    Landt, H.
    Univ Durham, Dept Phys, South Rd, Durham DH1 3LE, England.;Univ Durham, Ctr Adv Instrumentat, South Rd, Durham DH1 3LE, England..
    Lapington, J.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Laporte, P.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
    Lee, S.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Chuo Ku, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 2525210, Japan..
    Lees, J.
    Univ Savoie, CNRS, IN2P3, Lab Annecy le Vieux Phys Particules, 9 Chemin Bellevue BP 110, F-74941 Annecy Le Vieux, France..
    Lefaucheur, J.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
    Lenain, J. -P
    Leto, G.
    INAF Osservatorio Astrofis Catania, Via S Sofia 78, I-95123 Catania, Italy..
    Lindfors, E.
    Univ Turku, Tuorla Observ, FI-21500 Piikkio, Finland..
    Lohse, T.
    Humboldt Univ, Dept Phys, Newtonstr 15, D-12489 Berlin, Germany..
    Lombardi, S.
    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Monte Porzio Catone, Italy..
    Longo, F.
    Univ Trieste, Trieste, Italy.;INFN, Sezione Trieste, Trieste, Italy..
    Lopez, M.
    Univ Complutense Madrid, Grp Altas Energias, Av Complutense S-N, E-28040 Madrid, Spain..
    Lucarelli, F.
    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Monte Porzio Catone, Italy..
    Luque-Escamilla, P. L.
    Univ Jaen, Escuela Politecn Super Jaen, Campus Las Lagunillas S-N,Edif A3, E-23071 Jaen, Spain..
    Lopez-Coto, R.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
    Maccarone, M. C.
    INAF Ist Astrofis Spaziale & Fis Cosm Palermo, Via U La Malfa 153, I-90146 Palermo, Italy..
    Maier, G.
    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
    Malaguti, G.
    Ist Astrofis Spaziale & Fis Cosm Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy..
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    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
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    BAS, Inst Nucl Res & Nucl Energy, 72 Blvd Tsarigradsko Chaussee, Sofia 1784, Bulgaria..
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    CIEMAT, Avda Complutense 40, E-28040 Madrid, Spain..
    Marcowith, A.
    Univ Montpellier, CNRS, IN2P3, Lab Univers & Particules Montpellier, CC 72,Pl Eugene Bataillon, F-34095 Montpellier 5, France..
    Marti, J.
    Univ Jaen, Escuela Politecn Super Jaen, Campus Las Lagunillas S-N,Edif A3, E-23071 Jaen, Spain..
    Martinez, M.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
    Martinez, G.
    CIEMAT, Avda Complutense 40, E-28040 Madrid, Spain..
    Masuda, S.
    Kyoto Univ, Grad Sch Sci, Div Phys & Astron, Sakyo Ku, Kyoto 6068502, Japan..
    Maurin, G.
    Univ Savoie, CNRS, IN2P3, Lab Annecy le Vieux Phys Particules, 9 Chemin Bellevue BP 110, F-74941 Annecy Le Vieux, France..
    Maxted, N.
    Univ New South Wales, Sch Phys, Sydney, NSW 2052, Australia..
    Melioli, C.
    Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, R Matao 1226, BR-05508090 Sao Paulo, Brazil..
    Mineo, T.
    INAF Ist Astrofis Spaziale & Fis Cosm Palermo, Via U La Malfa 153, I-90146 Palermo, Italy..
    Mirabal, N.
    Univ Complutense Madrid, Grp Altas Energias, Av Complutense S-N, E-28040 Madrid, Spain..
    Mizuno, T.
    Hiroshima Univ, Hiroshima Astrophys Sci Ctr, Hiroshima 7398526, Japan..
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    Polish Acad Sci, Copernicus Astron Ctr, Ul Bartycka 18, PL-00716 Warsaw, Poland..
    Mohammed, M.
    Heidelberg Univ, Landessternwarte, D-69117 Heidelberg, Germany..
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    Univ Geneva, Dept Phys Nucl & Corpusculaire, 24 Rue Gen Dufour, CH-1211 Geneva 4, Switzerland..
    Moralejo, A.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
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    Miyazaki Univ, Dept Appl Phys, 1-1 Gakuen Kibana Dai Nishi, Miyazaki 8892192, Japan..
    Morlino, G.
    Univ Aquila, Dipartimento Sci Fis & Chim, INFN, Via Vetoio 1, I-67100 Laquila, Italy.;Gran Sasso Sci Inst, Via Vetoio 1, I-67100 Laquila, Italy..
    Morselli, A.
    INFN, Sez Roma Tor Vergata, Via Ric Sci 1, I-00133 Rome, Italy..
    Moulin, E.
    CEA Saclay, CEA, IRFU, SPP, Bat 141, F-91191 Gif Sur Yvette, France..
    Mukherjee, R.
    Columbia Univ, Dept Phys, 538 West 120th St, New York, NY 10027 USA..
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    Univ Bath, Bath BA2 7AY, Avon, England..
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    Kitasato Univ, Sch Allied Hlth Sci, Sagamihara, Kanagawa 2288555, Japan..
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    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan..
    Nagataki, S.
    RIKEN, Inst Phys & Chem Res, 2-1 Hirosawa, Wako, Saitama 3510198, Japan..
    Nagayoshi, T.
    Saitama Univ, Grad Sch Sci & Engn, Sakura Ku, 255 Simo Ohkubo, Saitama City, Saitama 3388570, Japan..
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    Yamanashi Gakuin Univ, Fac Management Informat, Kofu, Yamanashi 4008575, Japan..
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    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan.;Max Planck Inst Phys & Astrophys, Fohringer Ring 6, D-80805 Munich, Germany..
    Nakamori, T.
    Yamagata Univ, Dept Phys, Yamagata, Yamagata 9908560, Japan..
    Nemmen, R.
    Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, R Matao 1226, BR-05508090 Sao Paulo, Brazil..
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    Polish Acad Sci, Henryk Niewodniczanski Inst Nucl Phys, Ul Radzikowskiego 152, PL-31342 Krakow, Poland..
    Nieto, D.
    Columbia Univ, Dept Phys, 538 West 120th St, New York, NY 10027 USA..
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    Univ Complutense Madrid, Grp Altas Energias, Av Complutense S-N, E-28040 Madrid, Spain..
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    Univ Bialystok, Fac Phys, Ul K Ciolkowskiego 1L, PL-15254 Bialystok, Poland..
    Nishijima, K.
    Tokai Univ, Dept Phys, 4-1-1 Kita Kaname, Hiratsuka, Kanagawa 2591292, Japan..
    Noda, K.
    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan.;Max Planck Inst Phys & Astrophys, Fohringer Ring 6, D-80805 Munich, Germany..
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    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
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    Charles Univ Prague, Inst Particle & Nucl Phys, V Holesovickach 2, Prague 18000 8, Czech Republic..
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    Ivan Franko Natl Univ Lviv, Astron Observ, 1 Univ Ska St, UA-79000 City Of Lviv, Ukraine..
    Nozaki, S.
    Kyoto Univ, Grad Sch Sci, Div Phys & Astron, Sakyo Ku, Kyoto 6068502, Japan..
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    Aoyama Gakuin Univ, Dept Math & Phys, Sagamihara, Kanagawa 2298558, Japan..
    Ohishi, M.
    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan..
    Ohm, S.
    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
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    Nagoya Univ, Inst Space Earth Environm Res, Chikusa Ku, Nagoya, Aichi 4648601, Japan..
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    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
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    Tokushima Univ, Grad Sch Sci & Technol, Tokushima 7708506, Japan..
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    INAF IRA, INAF, Ist Radioastron, Via Gobetti 101, Bologna, Italy..
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    Jagiellonian Univ, Fac Phys Astron & Appl Comp Sci, Ul Prof Stanislawa Lojasiewicza 11, PL-30348 Krakow, Poland..
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    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
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    Univ Montpellier, CNRS, IN2P3, Lab Univers & Particules Montpellier, CC 72,Pl Eugene Bataillon, F-34095 Montpellier 5, France..
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    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
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    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
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    Univ Barcelona, Inst Ciencies Cosmos, IEEC UB, Dept Fis Quant & Astrofis, Marti & Franques 1, E-08028 Barcelona, Spain..
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    Ecole Polytech, CNRS, UMR 7638, Lab Leprince Ringuet, F-91128 Palaiseau, France..
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    Max Planck Inst Phys & Astrophys, Fohringer Ring 6, D-80805 Munich, Germany..
    Persic, M.
    Univ Udine, Via Sci 208, I-33100 Udine, Italy.;INFN, Sez Trieste, Via Sci 208, I-33100 Udine, Italy.;Osserv Astron Trieste, Via Sci 208, I-33100 Udine, Italy.;Ist Nazl Fis Nucl, Sez Trieste, Via Sci 208, I-33100 Udine, Italy..
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    Univ Joseph Fourier, INSU CNRS, Inst Planetol & Astrophys Grenoble, 621 Ave Cent,Domaine Univ, F-38041 Grenoble 9, France..
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    Inst Appl Problems Mech & Math, 3B Naukova St, UA-79060 Lvov, Ukraine..
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    Univ Bialystok, Fac Phys, Ul K Ciolkowskiego 1L, PL-15254 Bialystok, Poland..
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    Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Golm, Germany..
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    Univ Geneva, Dept Phys Nucl & Corpusculaire, 24 Rue Gen Dufour, CH-1211 Geneva 4, Switzerland..
    Prandini, E.
    Univ Geneva, Observ Geneva, ISDC Data Ctr Astrophys, Chemin Ecogia 16, CH-1290 Versoix, Switzerland..
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    Univ Savoie, CNRS, IN2P3, Lab Annecy le Vieux Phys Particules, 9 Chemin Bellevue BP 110, F-74941 Annecy Le Vieux, France..
    Principe, G.
    Univ Erlangen Nurnberg, Inst Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
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    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
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    Univ Coll Dublin, Dublin 4, Ireland..
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    Univ Tubingen, Inst Astron & Astrophys, Sand 1, D-72076 Tubingen, Germany..
    Quirrenbach, A.
    Heidelberg Univ, Landessternwarte, D-69117 Heidelberg, Germany..
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    Univ Geneva, Dept Phys Nucl & Corpusculaire, 24 Rue Gen Dufour, CH-1211 Geneva 4, Switzerland..
    Reimer, O.
    Leopold Franzens Univ, Inst Astro & Teilchenphys, Technikerstr 25-8, A-6020 Innsbruck, Austria..
    Renaud, M.
    Univ Montpellier, CNRS, IN2P3, Lab Univers & Particules Montpellier, CC 72,Pl Eugene Bataillon, F-34095 Montpellier 5, France..
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    Univ Barcelona, Inst Ciencies Cosmos, IEEC UB, Dept Fis Quant & Astrofis, Marti & Franques 1, E-08028 Barcelona, Spain..
    Rico, J.
    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
    Rizi, V.
    Univ Aquila, Dipartimento Sci Fis & Chim, INFN, Via Vetoio 1, I-67100 Laquila, Italy.;Gran Sasso Sci Inst, Via Vetoio 1, I-67100 Laquila, Italy..
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    CEA Saclay, CEA, IRFU, SAp, Bat 709, F-91191 Gif Sur Yvette, France..
    Fernandez, G. Rodriguez
    INFN, Sez Roma Tor Vergata, Via Ric Sci 1, I-00133 Rome, Italy..
    Rodriguez Vazquez, J. J.
    CIEMAT, Avda Complutense 40, E-28040 Madrid, Spain..
    Romano, P.
    INAF Ist Astrofis Spaziale & Fis Cosm Palermo, Via U La Malfa 153, I-90146 Palermo, Italy..
    Romeo, G.
    INAF Osservatorio Astrofis Catania, Via S Sofia 78, I-95123 Catania, Italy..
    Rosado, J.
    Univ Complutense Madrid, Grp Altas Energias, Av Complutense S-N, E-28040 Madrid, Spain..
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    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
    Rowell, G.
    Univ Adelaide, Sch Phys Sci, Adelaide, SA 5005, Australia..
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    Polish Acad Sci, Copernicus Astron Ctr, Ul Bartycka 18, PL-00716 Warsaw, Poland..
    Sadeh, I.
    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
    Safi-Harb, S.
    Univ Manitoba, 540 Machray Hall, Winnipeg, MB R3T 2N2, Canada..
    Saito, T.
    Kyoto Univ, Grad Sch Sci, Div Phys & Astron, Sakyo Ku, Kyoto 6068502, Japan..
    Sakaki, N.
    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan..
    Sanchez, D.
    Univ Savoie, CNRS, IN2P3, Lab Annecy le Vieux Phys Particules, 9 Chemin Bellevue BP 110, F-74941 Annecy Le Vieux, France..
    Sangiorgi, P.
    INAF Ist Astrofis Spaziale & Fis Cosm Palermo, Via U La Malfa 153, I-90146 Palermo, Italy..
    Sano, H.
    Nagoya Univ, Dept Phys & Astrophys, Chikusa Ku, Nagoya, Aichi 4648602, Japan..
    Santander, M.
    Columbia Univ, Dept Phys, 538 West 120th St, New York, NY 10027 USA..
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    Univ Oxford, Dept Phys, 1 Keble Rd, Oxford OX1 3NP, England..
    Sawada, M.
    Aoyama Gakuin Univ, Dept Math & Phys, Sagamihara, Kanagawa 2298558, Japan..
    Schioppa, E. J.
    Univ Geneva, Dept Phys Nucl & Corpusculaire, 24 Rue Gen Dufour, CH-1211 Geneva 4, Switzerland..
    Schoorlemmer, H.
    Max Planck Inst Kernphys, Saupfercheckweg 1, D-69117 Heidelberg, Germany..
    Schovanek, P.
    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
    Schussler, F.
    CEA Saclay, CEA, IRFU, SPP, Bat 141, F-91191 Gif Sur Yvette, France..
    Sergijenko, O.
    Ivan Franko Natl Univ Lviv, Astron Observ, 1 Univ Ska St, UA-79000 City Of Lviv, Ukraine..
    Servillat, M.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
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    Univ Manitoba, 540 Machray Hall, Winnipeg, MB R3T 2N2, Canada..
    Shellard, R. C.
    Ctr Brasileiro Pesquisas Fis, Rua Xavier Sigaud 150, BR-22290180 Rio De Janeiro, Brazil..
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    Acad Comp Ctr CYFRONET AGH, Ul Nawojki 11, PL-30950 Krakow, Poland..
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    Univ Turku, Tuorla Observ, FI-21500 Piikkio, Finland..
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    INFN, Sez Bari, Via Orabona 4, I-70126 Bari, Italy..
    Sliusar, V.
    Univ Geneva, Observ Geneva, ISDC Data Ctr Astrophys, Chemin Ecogia 16, CH-1290 Versoix, Switzerland..
    Sol, H.
    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
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    Univ Nova Gorica, Lab Astroparticle Phys, Vipayska 13, Nova Gorica 5000, Slovenia..
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    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
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    Jagiellonian Univ, Fac Phys Astron & Appl Comp Sci, Ul Prof Stanislawa Lojasiewicza 11, PL-30348 Krakow, Poland..
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    Charles Univ Prague, Inst Particle & Nucl Phys, V Holesovickach 2, Prague 18000 8, Czech Republic..
    Stephan, M.
    Univ Amsterdam, Astron Inst Anton Pannekoek, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands..
    Stolarczyk, T.
    CEA Saclay, CEA, IRFU, SAp, Bat 709, F-91191 Gif Sur Yvette, France..
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    Univ Lodz, Fac Phys & Appl Comp Sci, Ul Pomorska 149-153, PL-90236 Lodz, Poland..
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    Acad Comp Ctr CYFRONET AGH, Ul Nawojki 11, PL-30950 Krakow, Poland..
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    INAF Osservatorio Astron Brera, Via Brera 28, I-20121 Milan, Italy..
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    Nagoya Univ, Inst Space Earth Environm Res, Chikusa Ku, Nagoya, Aichi 4648601, Japan..
    Takahashi, M.
    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan..
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    Yamagata Univ, Dept Phys, Yamagata, Yamagata 9908560, Japan..
    Tanaka, M.
    KEK High Energy Accelerator Org, Inst Particle & Nucl Studies, 1-1 Oho, Tsukuba, Ibaraki 3050801, Japan..
    Tanaka, S.
    Konan Univ, Dept Phys, Kobe, Hyogo 6588501, Japan..
    Tejedor, L. A.
    Univ Complutense Madrid, Grp Altas Energias, Av Complutense S-N, E-28040 Madrid, Spain..
    Telezhinsky, I.
    Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Golm, Germany..
    Temnikov, P.
    BAS, Inst Nucl Res & Nucl Energy, 72 Blvd Tsarigradsko Chaussee, Sofia 1784, Bulgaria..
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    Saitama Univ, Grad Sch Sci & Engn, Sakura Ku, 255 Simo Ohkubo, Saitama City, Saitama 3388570, Japan..
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    Univ Padua, Dipartimento Fis, Via Marzolo 8, I-35131 Padua, Italy..
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    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan.;Max Planck Inst Phys & Astrophys, Fohringer Ring 6, D-80805 Munich, Germany..
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    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Monte Porzio Catone, Italy..
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    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
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    Yamagata Univ, Dept Phys, Yamagata, Yamagata 9908560, Japan..
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    Inst Space Sci IEEC CSIC, Campus UAB,Caner Can Magrans S-N, E-08193 Cerdanyola Del Valles, Spain.;ICREA, Campus UAB,Caner Can Magrans S-N, E-08193 Cerdanyola Del Valles, Spain..
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    Ist Astrofis Spaziale & Fis Cosm Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy..
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    INAF Osservatorio Astron Brera, Via Brera 28, I-20121 Milan, Italy..
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    Cherenkov Telescope Array Observ, Saupfercheckweg 1, D-69117 Heidelberg, Germany..
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    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
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    Aix Marseille Univ, CNRS, IN2P3, CPPM, 163 Ave Luminy, F-13288 Marseille, France..
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    Ist Astrofis Spaziale & Fis Cosm Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy..
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    Tokai Univ, Dept Phys, 4-1-1 Kita Kaname, Hiratsuka, Kanagawa 2591292, Japan..
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    INFN, Sez Perugia, Via A Pascoli, I-06123 Perugia, Italy..
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    Osserv Astron Torino, INAF, Corso Fiume 4, I-10133 Turin, Italy..
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    Ist Nazl Fis Nucl, Sez Napoli, Via Cintia,Ed G, I-80126 Naples, Italy..
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    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
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    Univ Erlangen Nurnberg, Inst Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
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    Univ Wisconsin, 500 Lincoln Dr, Madison, WI 53706 USA..
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    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
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    Univ Sao Paulo, Inst Fis Sao Carlos, Ave Trabalhador Sao Carlense 400, BR-13566590 Sao Carlos, SP, Brazil..
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    INAF Ist Astrofis Spaziale & Fis Cosm Palermo, Via U La Malfa 153, I-90146 Palermo, Italy..
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    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
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    Ist Nazl Fis Nucl, Sez Torino, Via P Giuria 1, I-10125 Turin, Italy..
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    Univ Nova Gorica, Lab Astroparticle Phys, Vipayska 13, Nova Gorica 5000, Slovenia..
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    Acad Sci Czech Republic, Inst Phys, Slovance 1999-2, Prague 18221 8, Czech Republic..
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    Inst Astrofis Canarias, Via Lactea, E-38205 Tenerife, Spain..
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    Heidelberg Univ, Landessternwarte, D-69117 Heidelberg, Germany..
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    Max Planck Inst Phys & Astrophys, Fohringer Ring 6, D-80805 Munich, Germany.;Stockholm Univ, Univ Vagen 10 A, SE-10691 Stockholm, Sweden..
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    Univ Chicago, Enrico Fermi Inst, 5640 South Ellis Ave, Chicago, IL 60637 USA..
    Walter, R.
    Univ Geneva, Observ Geneva, ISDC Data Ctr Astrophys, Chemin Ecogia 16, CH-1290 Versoix, Switzerland..
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    IFAE, Barcelona Inst Sci & Technol, Campus UAB, E-08193 Bellaterra, Barcelona, Spain..
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    Univ Oxford, Dept Phys, 1 Keble Rd, Oxford OX1 3NP, England..
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    Iowa State Univ, Dept Phys & Astron, Zaffarano Hall, Ames, IA 50011 USA..
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    Univ Adelaide, Sch Phys Sci, Adelaide, SA 5005, Australia..
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    Max Planck Inst Kernphys, Saupfercheckweg 1, D-69117 Heidelberg, Germany..
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    Polish Acad Sci, Henryk Niewodniczanski Inst Nucl Phys, Ul Radzikowskiego 152, PL-31342 Krakow, Poland..
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    Univ Iowa, Dept Phys & Astron, Van Allen Hall, Iowa City, IA 52242 USA..
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    Univ Calif Santa Cruz, Santa Cruz Inst Particle Phys, 1156 High St, Santa Cruz, CA 95064 USA.;Univ Calif Santa Cruz, Dept Phys, 1156 High St, Santa Cruz, CA 95064 USA..
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    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
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    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
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    Konan Univ, Dept Phys, Kobe, Hyogo 6588501, Japan..
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    Nagoya Univ, Dept Phys & Astrophys, Chikusa Ku, Nagoya, Aichi 4648602, Japan..
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    Aoyama Gakuin Univ, Dept Math & Phys, Sagamihara, Kanagawa 2298558, Japan..
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    Ibaraki Univ, Fac Sci, Mito, Ibaraki 3108512, Japan..
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    Univ Nova Gorica, Lab Astroparticle Phys, Vipayska 13, Nova Gorica 5000, Slovenia..
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    Ibaraki Univ, Fac Sci, Mito, Ibaraki 3108512, Japan..
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    Tokai Univ, Dept Phys, 4-1-1 Kita Kaname, Hiratsuka, Kanagawa 2591292, Japan..
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    Nagoya Univ, Dept Phys & Astrophys, Chikusa Ku, Nagoya, Aichi 4648602, Japan..
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    Univ Tokyo, Inst Cosm Ray Res, 5-1-5 Kashi Wwanoha, Kashiwa, Chiba 2778582, Japan..
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    Heidelberg Univ, Landessternwarte, D-69117 Heidelberg, Germany..
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    INAF Osservatorio Astron Padova, Vicolo Osservatorio 5, I-35122 Padua, Italy..
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    Univ Barcelona, Inst Ciencies Cosmos, IEEC UB, Dept Fis Quant & Astrofis, Marti & Franques 1, E-08028 Barcelona, Spain..
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    Univ Nova Gorica, Lab Astroparticle Phys, Vipayska 13, Nova Gorica 5000, Slovenia..
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    Univ Nova Gorica, Lab Astroparticle Phys, Vipayska 13, Nova Gorica 5000, Slovenia..
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    Polish Acad Sci, Copernicus Astron Ctr, Ul Bartycka 18, PL-00716 Warsaw, Poland..
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    Observ Paris, CNRS, LUTH, 5 Pl Jules Janssen, F-92190 Meudon, France.;Observ Paris, CNRS, GEPI, 5 Pl Jules Janssen, F-92190 Meudon, France..
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    Ist Nazl Fis Nucl, Sez Torino, Via P Giuria 1, I-10125 Turin, Italy..
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    Taras Shevchenko Natl Univ Kyiv, Astron Observ, 60 Volodymyrska St, UA-01033 Kiev, Ukraine..
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    Univ Erlangen Nurnberg, Inst Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
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    DESY, Platanenallee 6, D-15738 Zeuthen, Germany..
    Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7-39462017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 840, no 2, 74Article in journal (Refereed)
    Abstract [en]

    We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7-3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy (VHE) gamma rays. Special attention is paid to exploring possible spatial (anti) correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H I emission. We present a series of simulated images of RX J1713.7-3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H I observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.

  • 2.
    Borwankar, Chinmay
    et al.
    Bhabha Atom Res Ctr, India.
    Bhatt, Nilay
    Bhabha Atom Res Ctr, India.
    Bhattacharyya, Subir
    Bhabha Atom Res Ctr, India.
    Rannot, R. C.
    Bhabha Atom Res Ctr, India.
    Tickoo, A. K.
    Bhabha Atom Res Ctr, India.
    Koul, R.
    Bhabha Atom Res Ctr, India.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Simulation studies of MACE-I: Trigger rates and energy thresholds2016In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 84, 97-106 p.Article in journal (Refereed)
    Abstract [en]

    The MACE (Major Atmospheric Cherenkov Experiment) is an upcoming Very High Energy (VHE) gamma-ray telescope, based on imaging atmospheric Cherenkov technique, being installed at Hanle, a high altitude astronomical site in Ladakh, India. Here we present Monte Carlo simulation studies of trigger rates and threshold energies of MACE in the zenith angle range of 0 degrees-60 degrees for on-axis gamma-ray coming from point source and various cosmic ray species. We have simulated the telescope's response to gamma-rays, proton, electron and alpha initiated atmospheric Extensive Air Showers (EAS) in the broad energy range of 5 GeV to 20 TeV. For gamma-rays we consider power law and log parabolic spectra while other particles are simulated with their respective cosmic ray spectrum. Trigger rates and threshold energies are estimated for the trigger configuration of 4 Close Cluster Nearest Neighbour(CCNN) pixels as implemented in MACE hardware, in combination with single channel discriminator threshold ranging from 6-10 photo electrons (pe). We find that MACE can achieve the gamma-ray trigger energy threshold of similar to 17 GeV (4 CCNN, 9 pe) at 0 degrees zenith angle for power law spectrum. The total trigger rate at 0 degrees zenith is expected to be similar to 650 Hz, with protons contributing similar to 80% to it. For the zenith range of 0 degrees-40 degrees we find that the telescope can achieve gamma-gray trigger threshold energies of similar to 22 GeV at 20 degrees zenith angle and similar to 40 GeV at 40 degrees zenith angle. Integral rates are also almost constant for this zenith angle range. At zenith angle of 60 degrees, trigger energy threshold increases to similar to 173 GeV and total integral rate falls down to similar to 305 Hz. (C) 2016 Elsevier B.V. All rights reserved.

  • 3.
    Buitink, S.
    et al.
    Radboud University Nijmegen, The Netherlands.
    Corstanje, A.
    Radboud University Nijmegen, The Netherlands.
    Enriquez, J. E.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; Science Park Amsterdam, The Netherlands ; Max Planck Institute for Radio Astronomy, Germany.
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Huege, T.
    Karlsruhe Institute of Technology (KIT), Germany.
    Nelles, A.
    Radboud University Nijmegen, The Netherlands.
    Rachen, J. P.
    Radboud University Nijmegen, The Netherlands.
    Schellart, P.
    Radboud University Nijmegen, The Netherlands.
    Scholten, O.
    University of Groningen, The Netherlands.
    ter Veen, S.
    Radboud University Nijmegen, The Netherlands.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Trinh, T. N. G.
    University of Groningen, The Netherlands.
    Method for high precision reconstruction of air shower Xmax using two-dimensional radio intensity profiles2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 90, no 8, 1-12 p., 082003Article in journal (Refereed)
    Abstract [en]

    The mass composition of cosmic rays contains important clues about their origin. Accurate measurements are needed to resolve longstanding issues such as the transition from Galactic to extra-Galactic origin and the nature of the cutoff observed at the highest energies. Composition can be studied by measuring the atmospheric depth of the shower maximum Xmax of air showers generated by high-energy cosmic rays hitting the Earth’s atmosphere. We present a new method to reconstruct Xmax based on radio measurements. The radio emission mechanism of air showers is a complex process that creates an asymmetric intensity pattern on the ground. The shape of this pattern strongly depends on the longitudinal development of the shower. We reconstruct Xmax by fitting two-dimensional intensity profiles, simulated with CoREAS, to data from the Low Frequency Array (LOFAR) radio telescope. In the dense LOFAR core, air showers are detected by hundreds of antennas simultaneously. The simulations fit the data very well, indicating that the radiation mechanism is now well understood. The typical uncertainty on the reconstruction of Xmax for LOFAR showers is 17  g/cm2.

  • 4.
    Buitink, S.
    et al.
    Vrije Universiteit Brussel, Belgium ; Radboud University Nijmegen, The Netherlands.
    Corstanje, A.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; ASTRON, The Netherlands ; Science Park Amsterdam, The Netherlands ; Max-Planck-Institut für Radioastronomie, Germany.
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Huege, T.
    Karlsruhe Institute of Technology (KIT), Germany.
    Nelles, A.
    University of California Irvine, USA.
    Rachen, J. P.
    Radboud University Nijmegen, The Netherlands.
    Rossetto, L.
    Radboud University Nijmegen, The Netherlands.
    Schellart, P.
    Radboud University Nijmegen, The Netherlands.
    Scholten, O.
    University of Groningen, The Netherlands ; Vrije Universiteit Brussel, Belgium.
    Ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Trinh, T. N. G.
    Anderson, J.
    Asgekar, A.
    Avruch, I. M.
    Bell, M. E.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bonafede, A.
    Breitling, F.
    Broderick, J. W.
    Brouw, W. N.
    Brüggen, M.
    Butcher, H. R.
    Carbone, D.
    Ciardi, B.
    Conway, J. E.
    de Gasperin, F.
    de Geus, E.
    Deller, A.
    Dettmar, R. -J
    van Diepen, G.
    Duscha, S.
    Eislöffel, J.
    Engels, D.
    Enriquez, J. E.
    Fallows, R. A.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J. M.
    Gunst, A. W.
    van Haarlem, M. P.
    Hassall, T. E.
    Heald, G.
    Hessels, J. W. T.
    Hoeft, M.
    Horneffer, A.
    Iacobelli, M.
    Intema, H.
    Juette, E.
    Karastergiou, A.
    Kondratiev, V. I.
    Kramer, M.
    Kuniyoshi, M.
    Kuper, G.
    van Leeuwen, J.
    Loose, G. M.
    Maat, P.
    Mann, G.
    Markoff, S.
    McFadden, R.
    McKay-Bukowski, D.
    McKean, J. P.
    Mevius, M.
    Mulcahy, D. D.
    Munk, H.
    Norden, M. J.
    Orru, E.
    Paas, H.
    Pandey-Pommier, M.
    Pandey, V. N.
    Pietka, M.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H. J. A.
    Scaife, A. M. M.
    Schwarz, D. J.
    Serylak, M.
    Sluman, J.
    Smirnov, O.
    Stappers, B. W.
    Steinmetz, M.
    Stewart, A.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Toribio, M. C.
    Vermeulen, R.
    Vocks, C.
    Vogt, C.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wijnholds, S. J.
    Wise, M. W.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    Zensus, J. A.
    A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations2016In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 531, no 7592, 70-73 p.Article in journal (Refereed)
    Abstract [en]

    Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 1017–1018 electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal1 comes from accelerators capable of producing cosmic rays of these energies2. Cosmic rays initiate air showers—cascades of secondary particles in the atmosphere—and their masses can be inferred from measurements of the atmospheric depth of the shower maximum3 (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground4. Current measurements5 have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays6, 7, 8 is a rapidly developing technique9 for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front6, 12. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 1017–1017.5 electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 1017.5 electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 1017–1017.5 electronvolt range.

  • 5.
    Buitink, Stijn
    et al.
    University of Groningen, The Netherlands ; Radboud University Nijmegen, The Netherlands.
    Corstanje, Arthur
    Radboud University Nijmegen, The Netherlands.
    Enriquez, Emilio
    Radboud University Nijmegen, The Netherlands.
    Falcke, Heino
    Radboud University Nijmegen, The Netherlands ; Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Frieswijk, Wilfred
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Hörandel, Jörg
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Mevius, Maaijke
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Nelles, Anna
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Schellart, Pim
    Radboud University Nijmegen, The Netherlands.
    Scholten, Olaf
    University of Groningen, The Netherlands.
    ter Veen, Sander
    Radboud University Nijmegen, The Netherlands.
    van den Akker, Martin
    Radboud University Nijmegen, The Netherlands.
    Searching for neutrino radio flashes from the Moon with LOFAR2013In: 5th International Workshop on Acoustic and Radio EeV Neutrino Detection Activities: Arena 2012 / [ed] Robert Lahmann, Thomas Eberl, Kay Graf, Clancy James, Tim Huege, Timo Karg, Rolf Nahnhauer, American Institute of Physics (AIP), 2013, Vol. 1535, 27-31 p.Conference paper (Refereed)
    Abstract [en]

    Ultra-high-energy neutrinos and cosmic rays produce short radio flashes through the Askaryan effect when they impact on the Moon. Earthbound radio telescopes can search the Lunar surface for these signals. A new generation of lowfrequency, digital radio arrays, spearheaded by LOFAR, will allow for searches with unprecedented sensitivity. In the first stage of the NuMoon project, low-frequency observations were carried out with the Westerbork Synthesis Radio Telescope, leading to the most stringent limit on the cosmic neutrino flux above 1023 eV. With LOFAR we will be able to reach a sensitivity of over an order of magnitude better and to decrease the threshold energy.

  • 6. Coenen, T.
    et al.
    van Leeuwen, J.
    Hessels, J. W. T.
    Stappers, B. W.
    Kondratiev, V. I.
    Alexov, A.
    Breton, R. P.
    Bilous, A.
    Cooper, S.
    Falcke, H.
    Fallows, R. A.
    Gajjar, V.
    Grießmeier, J. -M
    Hassall, T. E.
    Karastergiou, A.
    Keane, E. F.
    Kramer, M.
    Kuniyoshi, M.
    Noutsos, A.
    Os\lowski, S.
    Pilia, M.
    Serylak, M.
    Schrijvers, C.
    Sobey, C.
    ter Veen, S.
    Verbiest, J.
    Weltevrede, P.
    Wijnholds, S.
    Zagkouris, K.
    van Amesfoort, A. S.
    Anderson, J.
    Asgekar, A.
    Avruch, I. M.
    Bell, M. E.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bonafede, A.
    Breitling, F.
    Broderick, J.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    Corstanje, A.
    Deller, A.
    Duscha, S.
    Eislöffel, J.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    de Gasperin, F.
    de Geus, E.
    Gunst, A. W.
    Hamaker, J. P.
    Heald, G.
    Hoeft, M.
    van der Horst, A.
    Juette, E.
    Kuper, G.
    Law, C.
    Mann, G.
    McFadden, R.
    McKay-Bukowski, D.
    McKean, J. P.
    Munk, H.
    Orru, E.
    Paas, H.
    Pandey-Pommier, M.
    Polatidis, A. G.
    Reich, W.
    Renting, A.
    Röttgering, H.
    Rowlinson, A.
    Scaife, A. M. M.
    Schwarz, D.
    Sluman, J.
    Smirnov, O.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, C.
    Vermeulen, R.
    Vocks, C.
    van Weeren, R. J.
    Wucknitz, O.
    Zarka, P.
    Zensus, A.
    The LOFAR pilot surveys for pulsars and fast radio transients2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 570, 1-16 p., A60Article in journal (Refereed)
    Abstract [en]

    We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~ 1.4 × 104 deg2, with 1 h dwell times. Each observation covered ~75 deg2 using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFAR Tied-Array Survey (LOTAS), spanned ~600 deg2, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR “Superterp” stations, we formed 19 tied-array beams, together covering 4 deg2 per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of < 150 day-1 sky-1, for bursts brighter than S> 107  Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR or any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky surveys for pulsars and fast transients, and they set the stage for further surveying efforts using LOFAR and the planned low-frequency component of the Square Kilometer Array.

  • 7.
    Corstanje, A.
    et al.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Bonardi, A.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Buitink, S.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands.;Vrije Univ Brussel, Inst Astrophys, Pleinlaan 2, B-1050 Brussels, Belgium..
    Falcke, H.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands.;Netherlands Inst Radio Astron ASTRON, Postbus 2, NL-7990 AA Dwingeloo, Netherlands.;Nikhef, Sci Pk Amsterdam, NL-1098 XG Amsterdam, Netherlands.;Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany..
    Horandel, J. R.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands.;Nikhef, Sci Pk Amsterdam, NL-1098 XG Amsterdam, Netherlands..
    Mitra, R.
    Vrije Univ Brussel, Inst Astrophys, Pleinlaan 2, B-1050 Brussels, Belgium..
    Mulrey, K.
    Vrije Univ Brussel, Inst Astrophys, Pleinlaan 2, B-1050 Brussels, Belgium..
    Nelles, A.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands.;Nikhef, Sci Pk Amsterdam, NL-1098 XG Amsterdam, Netherlands.;Univ Calif Irvine, Dept Phys & Astron, Irvine, CA 92697 USA..
    Rachen, J. P.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Rossetto, L.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Schellart, P.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands.;Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA..
    Scholten, O.
    Vrije Univ Brussel, Interuniv Inst High Energy, Pleinlaan 2, B-1050 Brussels, Belgium.;Univ Groningen, POB 72, NL-9700 AB Groningen, Netherlands..
    ter Veen, S.
    Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands.
    Trinh, G.
    Univ Groningen, POB 72, NL-9700 AB Groningen, Netherlands..
    Winchen, T.
    Vrije Univ Brussel, Inst Astrophys, Pleinlaan 2, B-1050 Brussels, Belgium..
    The effect of the atmospheric refractive index on the radio signal of extensive air showers2017In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 89, 23-29 p.Article in journal (Refereed)
    Abstract [en]

    For the interpretation of measurements of radio emission from extensive air showers, an important systematic uncertainty arises from natural variations of the atmospheric refractive index n. At a given altitude, the refractivity N = 10(6) (n - 1) can have relative variations on the order of 10% depending on temperature, humidity, and air pressure. Typical corrections to be applied to N are about 4%. Using CoREAS simulations of radio emission from air showers, we have evaluated the effect of varying N on measurements of the depth of shower maximum X-max. For an observation band of 30-80 MHz, a difference of 4% in refractivity gives rise to a systematic error in the inferred X-max between 3.5 and 11 g/cm(2), for proton showers with zenith angles ranging from 15 to 50 degrees. At higher frequencies, from 120 to 250 MHz, the offset ranges from 10 to 22 g/cm(2). These offsets were found to be proportional to the geometric distance to X-max. We have compared the results to a simple model based on the Cherenkov angle. For the 120-250 MHz band, the model is in qualitative agreement with the simulations. In typical circumstances, we find a slight decrease in X-max compared to the default refractivity treatment in CoREAS. While this is within commonly treated systematic uncertainties, accounting for it explicitly improves the accuracy of X-max measurements. (C) 2017 Elsevier B.V. All rights reserved.

  • 8.
    Corstanje, A.
    et al.
    Radboud University Nijmegen, The Netherlands.
    Buitink, S.
    Vrije Universiteit Brussel, Belgium.
    Enriquez, J. E.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands ; Netherlands Institute for Radio Astronomy, The Netherlands ; Max Planck Institute for Radio Astronomy, Germany.
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Krause, M.
    Deutsches Elektronen-Synchrotron, Germany.
    Nelles, A.
    Radboud University Nijmegen, The Netherlands ; University of California Irvine, USA.
    Rachen, J. P.
    Radboud University Nijmegen, The Netherlands.
    Schellart, P.
    Radboud University Nijmegen, The Netherlands.
    Scholten, O.
    University Groningen, The Netherlands ; Vrije Universiteit Brussel, Belgium.
    ter Veen, S.
    Radboud University Nijmegen, The Netherlands.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Trinh, T. N. G.
    University Groningen, The Netherlands.
    Timing calibration and spectral cleaning of LOFAR time series data2016Manuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    We describe a method for spectral cleaning and timing calibration of short voltage time series data from individual radio interferometer receivers. It makes use of the phase differences in Fast Fourier Transform (FFT) spectra across antenna pairs. For strong, localized terrestrial sources these are stable over time, while being approximately uniform-random for a sum over many sources or for noise. Using only milliseconds-long datasets, the method finds the strongest interfering transmitters, a first-order solution for relative timing calibrations, and faulty data channels. No knowledge of gain response or quiescent noise levels of the receivers is required. With relatively small data volumes, this approach is suitable for use in an online system monitoring setup for interferometric arrays. We have applied the method to our cosmic-ray data collection, a collection of measurements of short pulses from extensive air showers, recorded by the LOFAR radio telescope. Per air shower, we have collected 2 ms of raw time series data for each receiver. The spectral cleaning has a calculated optimal sensitivity corresponding to a power signal-to-noise ratio of 0.08 (or -11 dB) in a spectral window of 25 kHz, for 2 ms of data in 48 antennas. This is well sufficient for our application. Timing calibration across individual antenna pairs has been performed at 0.4 ns precision; for calibration of signal clocks across stations of 48 antennas the precision is 0.1 ns. Monitoring differences in timing calibration per antenna pair over the course of the period 2011 to 2015 shows a precision of 0.08 ns, which is useful for monitoring and correcting drifts in signal path synchronizations. A cross-check method for timing calibration is presented, using a pulse transmitter carried by a drone flying over the array. Timing precision is similar, 0.3 ns.

  • 9. Corstanje, A.
    et al.
    Schellart, P.
    Nelles, A.
    Buitink, S.
    Enriquez, J. E.
    Falcke, H.
    Frieswijk, W.
    Hörandel, J. R.
    Krause, M.
    Rachen, J. P.
    Scholten, O.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Trinh, T. N. G.
    van den Akker, M.
    Alexov, A.
    Anderson, J.
    Avruch, I. M.
    Bell, M. E.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bonafede, A.
    Breitling, F.
    Broderick, J.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    de Gasperin, F.
    de Geus, E.
    de Vos, M.
    Duscha, S.
    Eislöffel, J.
    Engels, D.
    Fallows, R. A.
    Ferrari, C.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Hamaker, J. P.
    Hoeft, M.
    Horneffer, A.
    Iacobelli, M.
    Juette, E.
    Karastergiou, A.
    Kohler, J.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Kuper, G.
    Maat, P.
    Mann, G.
    McFadden, R.
    McKay-Bukowski, D.
    Mevius, M.
    Munk, H.
    Norden, M. J.
    Orru, E.
    Paas, H.
    Pandey-Pommier, M.
    Pandey, V. N.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Scaife, A. M. M.
    Schwarz, D.
    Smirnov, O.
    Stewart, A.
    Steinmetz, M.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Toribio, C.
    Vermeulen, R.
    Vocks, C.
    van Weeren, R. J.
    Wijnholds, S. J.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    The shape of the radio wavefront of extensive air showers as measured with LOFAR2015In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 61, 22-31 p.Article in journal (Refereed)
    Abstract [en]

    Extensive air showers, induced by high energy cosmic rays impinging on the Earth’s atmosphere, produce radio emission that is measured with the LOFAR radio telescope. As the emission comes from a finite distance of a few kilometers, the incident wavefront is non-planar. A spherical, conical or hyperbolic shape of the wavefront has been proposed, but measurements of individual air showers have been inconclusive so far. For a selected high-quality sample of 161 measured extensive air showers, we have reconstructed the wavefront by measuring pulse arrival times to sub-nanosecond precision in 200 to 350 individual antennas. For each measured air shower, we have fitted a conical, spherical, and hyperboloid shape to the arrival times. The fit quality and a likelihood analysis show that a hyperboloid is the best parameterization. Using a non-planar wavefront shape gives an improved angular resolution, when reconstructing the shower arrival direction. Furthermore, a dependence of the wavefront shape on the shower geometry can be seen. This suggests that it will be possible to use a wavefront shape analysis to get an additional handle on the atmospheric depth of the shower maximum, which is sensitive to the mass of the primary particle.

  • 10.
    Corstanje, A.
    et al.
    Radboud University Nijmegen, The Netherlands.
    van den Akker, M.
    Radboud University Nijmegen, The Netherlands.
    Bähren, L.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; Kernfysisch Versneller Instituut, The Netherlands.
    Frieswijk, W.
    Kernfysisch Versneller Instituut, The Netherlands.
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands.
    Horneffer, A.
    Radboud University Nijmegen, The Netherlands.
    James, C. W.
    Radboud University Nijmegen, The Netherlands.
    Kelley, J. L.
    Radboud University Nijmegen, The Netherlands.
    McFadden, R.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Mevius, M.
    Kernfysisch Versneller Instituut, The Netherlands.
    Nelles, A.
    Radboud University Nijmegen, The Netherlands.
    Schellart, P.
    Radboud University Nijmegen, The Netherlands.
    Scholten, O.
    Kernfysisch Versneller Instituut, The Netherlands.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    ter Veen, S.
    Radboud University Nijmegen, The Netherlands.
    LOFAR: Detecting Cosmic Rays with a Radio Telescope2011In: Proceedings of the 32nd International Cosmic Ray Conference: Aug. 11-18, 2011. Beijing, China, International Union of Pure and Applied Physics (IUPAP) , 2011, Vol. 3, 192-195 p.Conference paper (Other academic)
    Abstract [en]

    LOFAR (the Low Frequency Array), a distributed digital radio telescope with stations in the Netherlands, Germany, France, Sweden, and the United Kingdom, is designed to enable full-sky monitoring of transient radio sources. These capabilities are ideal for the detection of broadband radio pulses generated in cosmic ray air showers. The core of LOFAR consists of 24 stations within 4 square kilometers, and each station contains 96 low-band antennas and 48 high-band antennas. This dense instrumentation will allow detailed studies of the lateral distribution of the radio signal in a frequency range of 10-250 MHz. Such studies are key to understanding the various radio emission mechanisms within the air shower, as well as for determining the potential of the radio technique for primary particle identification. We present the status of the LOFAR cosmic ray program, including the station design and hardware, the triggering and filtering schemes, and our initial observations of cosmic-ray-induced radio pulses.

  • 11.
    Dhar, V. K.
    et al.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Yadav, K. K.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Dubey, B. P.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Sahyanathan, S.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    ANN based energy estimation procedure and energy spectrum of the Crab Nebula as measured by the TACTIC gamma-ray telescope2005In: 29th International Cosmic Ray Conference Pune (2005), 2005, Vol. 4, 179-182 p.Conference paper (Refereed)
    Abstract [en]

    A novel energy reconstruction procedure based on the utilization of Articial Neural Network has been developedfor the TACTIC atmospheric Cerenkov imaging telescope to estimate the energy of the primary gammaraysin the TeV energy range. The procedure uses a 3:20:1 conguration of the ANN with resilient backpropagationtraining algorithm to estimate the energy of a-ray like event on the basis of its image SIZE,DISTANCE and zenith angle. The results obtained by using the CORSIKA code simulated data suggest theenergy resolution of the telescope is40for retaining90of the-ray events in a particular energybin which is comparable to the energy resolution of other single element imaging telescopes. Details of theenergy estimation procedure along with results obtained by determining the Crab Nebula energy spectrum inthe energy range 1-16 TeV as measured by the TACTIC telescope are presented in the paper.

  • 12. Ebert, U.
    et al.
    Trinh, G. T. N.
    Buitink, S.
    Corstanje, A.
    Enriquez, J. E.
    Falcke, H.
    Horandel, J.
    Koehn, C.
    Nelles, A.
    Rachen, J. P.
    Rutjes, C.
    Schellart, P.
    Scholten, O.
    ter Veen, S.
    Thoudam, Satyendra
    Determining atmospheric electric fields from the radio footprint of cosmic-ray induced extensive air showers as measured with LOFAR2014In: AGU Fall Meeting Abstracts 2014, 2014Conference paper (Refereed)
  • 13.
    Garsden, H.
    et al.
    Université Paris Diderot, France.
    Girard, J. N.
    Université Paris Diderot, France.
    Starck, J. L.
    Université Paris Diderot, France.
    Corbel, S.
    Université Paris Diderot, France.
    Tasse, C.
    Rhodes University, South Africa ; SKA South Africa, South Africa.
    Woiselle, A.
    Sagem (Safran), France ; Université Paris Diderot, France.
    McKean, J. P.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    van Amesfoort, A. S.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Anderson, J.
    Helmholtz-Zentrum Potsdam, Germany ; Leibniz-Institut für Astrophysik Potsdam (AIP), Germany.
    Avruch, I. M.
    SRON Netherlands Institute for Space Research, The Netherlands ; Kapteyn Astronomical Institute, The Netherlands .
    Beck, R.
    Max-Planck-Institut für Radioastronomie, Germany .
    Bentum, M. J.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; University of Twente, Germany .
    Best, P.
    University of Edinburgh, UK.
    Breitling, F.
    Leibniz-Institut für Astrophysik Potsdam (AIP), Germany.
    Broderick, J.
    University of Southampton, UK.
    Brüggen, M.
    University of Hamburg, Germany.
    Butcher, H. R.
    Australian National University, Australia .
    Ciardi, B.
    Max Planck Institute for Astrophysics, Germany.
    de Gasperin, F.
    University of Hamburg, Germany.
    de Geus, E.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; SmarterVision BV, The Netherlands .
    de Vos, M.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Duscha, S.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Eislöffel, J.
    Thüringer Landessternwarte, Germany.
    Engels, D.
    Hamburger Sternwarte, Germany.
    Falcke, H.
    Department of Astrophysics/IMAPP, The Netherlands ; Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Fallows, R. A.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Fender, R.
    University of Oxford, UK.
    Ferrari, C.
    Université de Nice Sophia-Antipolis, France.
    Frieswijk, W.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Garrett, M. A.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; Leiden University, The Netherlands .
    Grießmeier, J.
    Universite d’Orléans/CNRS, France ; Observatoire de Paris – CNRS/INSU, France.
    Gunst, A. W.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Hassall, T. E.
    University of Southampton, UK ; The University of Manchester, UK.
    Heald, G.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Hoeft, M.
    Thüringer Landessternwarte, Germany.
    Hörandel, J.
    Radboud University Nijmegen, The Netherlands .
    van der Horst, A.
    University of Amsterdam, The Netherlands.
    Juette, E.
    Astronomisches Institut der Ruhr-Universität Bochum, Germany.
    Karastergiou, A.
    University of Oxford, UK.
    Kondratiev, V. I.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; Astro Space Center of the Lebedev Physical Institute, Russia .
    Kramer, M.
    Max-Planck-Institut für Radioastronomie, Germany ; The University of Manchester, UK.
    Kuniyoshi, M.
    Max-Planck-Institut für Radioastronomie, Germany.
    Kuper, G.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Mann, G.
    Leibniz-Institut für Astrophysik Potsdam (AIP), Germany .
    Markoff, S.
    University of Amsterdam, The Netherlands.
    McFadden, R.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    McKay-Bukowski, D.
    University of Oulu, Finland ; University of Groningen, he Netherlands .
    Mulcahy, D. D.
    Max-Planck-Institut für Radioastronomie, Germany.
    Munk, H.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Norden, M. J.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Orru, E.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Paas, H.
    University of Groningen, The Netherlands .
    Pandey-Pommier, M.
    Observatoire de Lyon, France.
    Pandey, V. N.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Pietka, G.
    University of Oxford, UK.
    Pizzo, R.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Polatidis, A. G.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Renting, A.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Röttgering, H.
    Leiden University, The Netherlands.
    Rowlinson, A.
    University of Amsterdam, The Netherlands .
    Schwarz, D.
    Universität Bielefeld, Germany .
    Sluman, J.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Smirnov, O.
    Rhodes University, South Africa ; SKA South Africa, South Africa.
    Stappers, B. W.
    The University of Manchester, UK.
    Steinmetz, M.
    Leibniz-Institut für Astrophysik Potsdam (AIP), Germany.
    Stewart, A.
    University of Oxford, UK.
    Swinbank, J.
    University of Amsterdam, The Netherlands .
    Tagger, M.
    LPC2E – Universite d’Orléans/CNRS, France.
    Tang, Y.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands .
    Toribio, C.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Vermeulen, R.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Vocks, C.
    Leibniz-Institut für Astrophysik Potsdam (AIP), Germany.
    van Weeren, R. J.
    Harvard-Smithsonian Center for Astrophysics, USA.
    Wijnholds, S. J.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Wise, M. W.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; University of Amsterdam, The Netherlands .
    Wucknitz, O.
    Max-Planck-Institut für Radioastronomie, Germany.
    Yatawatta, S.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands .
    Zarka, P.
    Observatoire de Paris, France.
    Zensus, A.
    Max-Planck-Institut für Radioastronomie, Germany .
    LOFAR sparse image reconstruction2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 575, no A90Article in journal (Refereed)
    Abstract [en]

    Context. The LOw Frequency ARray (LOFAR) radio telescope is a giant digital phased array interferometer with multiple antennas distributed in Europe. It provides discrete sets of Fourier components of the sky brightness. Recovering the original brightness distribution with aperture synthesis forms an inverse problem that can be solved by various deconvolution and minimization methods.

    Aims. Recent papers have established a clear link between the discrete nature of radio interferometry measurement and the “compressed sensing” (CS) theory, which supports sparse reconstruction methods to form an image from the measured visibilities. Empowered by proximal theory, CS offers a sound framework for efficient global minimization and sparse data representation using fast algorithms. Combined with instrumental direction-dependent effects (DDE) in the scope of a real instrument, we developed and validated a new method based on this framework.

    Methods. We implemented a sparse reconstruction method in the standard LOFAR imaging tool and compared the photometric and resolution performance of this new imager with that of CLEAN-based methods (CLEAN and MS-CLEAN) with simulated and real LOFAR data.

    Results. We show that i) sparse reconstruction performs as well as CLEAN in recovering the flux of point sources; ii) performs much better on extended objects (the root mean square error is reduced by a factor of up to 10); and iii) provides a solution with an effective angular resolution 2−3 times better than the CLEAN images.

    Conclusions. Sparse recovery gives a correct photometry on high dynamic and wide-field images and improved realistic structures of extended sources (of simulated and real LOFAR datasets). This sparse reconstruction method is compatible with modern interferometric imagers that handle DDE corrections (A- and W-projections) required for current and future instruments such as LOFAR and SKA.

  • 14.
    Girard, J. N.
    et al.
    Rhodes University, South Africa ; SKA South Africa, South Africa ; CEA Saclay, France.
    Zarka, P.
    Paris Observatory, France.
    Tasse, C.
    Paris Observatory, France.
    Hess, S.
    ONERA, France.
    de Pater, I.
    University of California, USA.
    Santos-Costa, D.
    Southwest Research Institute, USA.
    Nenon, Q.
    ONERA, France.
    Sicard, A.
    ONERA, France.
    Bourdarie, S.
    ONERA, France.
    Anderson, J.
    Hlmholtz Centre Potsdam, Germany.
    Asgekar, A.
    Bell, M. E.
    van Bemmel, I.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bonafede, A.
    Breitling, F.
    Breton, R. P.
    Broderick, J. W.
    Brouw, W. N.
    Brüggen, M.
    Ciardi, B.
    Corbel, S.
    Corstanje, A.
    de Gasperin, F.
    de Geus, E.
    Deller, A.
    Duscha, S.
    Eislöffel, J.
    Falcke, H.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Hessels, J. W. T.
    Hoeft, M.
    Hörandel, J.
    Iacobelli, M.
    Juette, E.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Kuper, G.
    van Leeuwen, J.
    Loose, M.
    Maat, P.
    Mann, G.
    Markoff, S.
    McFadden, R.
    McKay-Bukowski, D.
    Moldon, J.
    Munk, H.
    Nelles, A.
    Norden, M. J.
    Orru, E.
    Paas, H.
    Pandey-Pommier, M.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Rowlinson, A.
    Schwarz, D.
    Smirnov, O.
    Steinmetz, M.
    Swinbank, J.
    Tagger, M.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, M. C.
    Vermeulen, R.
    Vocks, C.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wucknitz, O.
    Imaging Jupiter’s radiation belts down to 127 MHz with LOFAR2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, A3Article in journal (Refereed)
    Abstract [en]

    Context. With the limited amount of in situ particle data available for the innermost region of Jupiter’s magnetosphere, Earth-based observations of the giant planets synchrotron emission remain the sole method today of scrutinizing the distribution and dynamical behavior of the ultra energetic electrons magnetically trapped around the planet. Radio observations ultimately provide key information about the origin and control parameters of the harsh radiation environment.

    Aims. We perform the first resolved and low-frequency imaging of the synchrotron emission with LOFAR. At a frequency as low as 127 MHz, the radiation from electrons with energies of ~1–30 MeV are expected, for the first time, to be measured and mapped over a broad region of Jupiter’s inner magnetosphere.

    Methods. Measurements consist of interferometric visibilities taken during a single 10-hour rotation of the Jovian system. These visibilities were processed in a custom pipeline developed for planetary observations, combining flagging, calibration, wide-field imaging, direction-dependent calibration, and specific visibility correction for planetary targets. We produced spectral image cubes of Jupiter’s radiation belts at the various angular, temporal, and spectral resolutions from which flux densities were measured.

    Results. The first resolved images of Jupiter’s radiation belts at 127–172 MHz are obtained with a noise level ~20–25 mJy/beam, along with total integrated flux densities. They are compared with previous observations at higher frequencies. A greater extent of the synchrotron emission source (≥4 RJ) is measured in the LOFAR range, which is the signature – as at higher frequencies – of the superposition of a “pancake” and an isotropic electron distribution. Asymmetry of east-west emission peaks is measured, as well as the longitudinal dependence of the radial distance of the belts, and the presence of a hot spot at λIII = 230° ± 25°. Spectral flux density measurements are on the low side of previous (unresolved) ones, suggesting a low-frequency turnover and/or time variations of the Jovian synchrotron spectrum.

    Conclusions. LOFAR proves to be a powerful and flexible planetary imager. In the case of Jupiter, observations at 127 MHz depict the distribution of ~1–30 MeV energy electrons up to ~4–5 planetary radii. The similarities of the observations at 127 MHz with those at higher frequencies reinforce the conclusion that the magnetic field morphology primarily shapes the brightness distribution features of Jupiter’s synchrotron emission, as well as how the radiating electrons are likely radially and latitudinally distributed inside about 2 planetary radii. Nonetheless, the detection of an emission region that extends to larger distances than at higher frequencies, combined with the overall lower flux density, yields new information on Jupiter’s electron distribution, and this information may ultimately shed light on the origin and mode of transport of these particles.

  • 15.
    Godambe, S. V.
    et al.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Baliyan, K. S.
    Physical Research Laboratory, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Yadav, K. K.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Chanchalani, K.
    Bhabha Atomic Research Centre, India.
    Ganesh, S.
    Physical Research Laboratory, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Joshi, U. C.
    Physical Research Laboratory, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Sahaynathan, S.
    Bhabha Atomic Research Centre, India.
    Shah, C.
    Physical Research Laboratory, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    Very high energy γ-ray and near infrared observations of 1ES2344+514 during 2004 052007In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 34, 1683-1695 p.Article in journal (Refereed)
    Abstract [en]

    We have observed the BL Lac object 1ES2344+514 (z = 0.044) in very high energy (VHE) gamma-ray and near-infrared wavelength bands with TACTIC and MIRO telescopes, respectively. The observations were made from 18th October to 9th December 2004 and 27th October 2005 to 1st January 2006. Detailed analysis of the TACTIC data indicates the absence of a statistically significant gamma-ray signal both in overall data and on a nightly basis from the source direction. We estimate an upper limit of I(≥1.5 TeV) ≤ 3.84 × 10−12 photons cm−2 s−1 at a 3σ confidence level on the integrated γ-ray flux. In addition, we have also compared TACTIC TeV light curves with those of the RXTE ASM (2–12 keV) for the contemporary period and find that there are no statistically significant increases in the signal strengths from the source in both these energy regions. During 2004 IR observations, 1ES2344+514 shows low level (0.06 magnitude) day-to-day variation in both, J and H bands. However, during the 2005 observation epoch, the source brightens up by about 0.41 magnitude from its October 2005 level J magnitude = 12.64 to J = 12.23 on December 6, 2005. It then fades by about 0.2 magnitude during 6 to 10 December, 2005. The variation is seen in both, J and H, bands simultaneously. The light travel time arguments suggest that the emission region size is of the order of 1017 cm.

  • 16.
    Godambe, S. V.
    et al.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Yadav, K. K.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Chanchalani, K.
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Sahaynathan, B. S.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Very high energy γ-ray observations of Mrk 501 using the TACTIC imaging γ-ray telescope during 2005 062008In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 35, no 6, 065202Article in journal (Refereed)
    Abstract [en]

    In this paper we report on the Markarian 501 results obtained during our TeV γ-ray observations from 11 March to 12 May 2005 and 28 February to 7 May 2006 for 112.5 h with the TACTIC γ-ray telescope. During 2005 observations for 45.7 h, the source was found to be in a low state and we have placed an upper limit of 4.62 × 10−12 photons cm−2 s−1 at 3σ level on the integrated TeV γ-ray flux above 1 TeV from the source direction. However, during 2006 observations for 66.8 h, detailed data analysis revealed the presence of a TeV γ-ray signal from the source with a statistical significance of 7.5σ above Eγ≥ 1 TeV. The time-averaged differential energy spectrum of the source in the energy range 1–11 TeV is found to match well with the power-law function of the form (dΦ/dE = f0E−Γ) with f0 = (1.66 ± 0.52) × 10−11 cm−2 s−1 TeV−1 and Γ = 2.80 ± 0.27.

  • 17.
    Godambe, S. V.
    et al.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Sahayanathan, S.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    Physical Research Laboratory, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Yadav, K. K.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Baliyan, K. S.
    Physical Research Laboratory, India.
    Joshi, U. C.
    Physical Research Laboratory, India.
    Ganesh, S.
    Physical Research Laboratory, India.
    Shah, C.
    Physical Research Laboratory, India.
    Ohlan, A.
    Physical Research Laboratory, India.
    Very High Energy Gamma-ray and Near Infrared observations of 1ES2344+514 with TACTIC and MIRO Telescopes2005In: 29th International Cosmic Ray Conference Pune (2005), 2005, Vol. 4Conference paper (Refereed)
    Abstract [en]

    1ES2344+514 (z = 0.04) is one of the rst BL Lac objects to be reported as an extreme synchrotron blazar withsynchotron peak energy reaching up to 100keV and was discovered as a source of Very High Energy (VHE)gamma- rays by the Whipple group in 1995. Subsequently, it was observed by the HEGRA group in 1997/98and 2002. We have recently (Oct.- Dec. 2004) observed the 1ES2344+514 using the imaging element of theTACTIC array and have collected data for 53 hours in on/off mode. The source was also observed in nearinfrared bands J, H and K, for some nights using NICMOS-3 array mounted on 1.2m MIRO infrared telescope.Such a study is expected to provide clues to the dominance or otherwise of the Compton component. Afterdetailed analysis of the TACTIC data we have placed an upper limit of    photons cmsata 3condence level on the gamma-ray ux from the source. In the near infrared band the source shows lowlevel variations without any aring activity.

  • 18. Heald, G. H.
    et al.
    Pizzo, R. F.
    Orrú, E.
    Breton, R. P.
    Carbone, D.
    Ferrari, C.
    Hardcastle, M. J.
    Jurusik, W.
    Macario, G.
    Mulcahy, D.
    Rafferty, D.
    Asgekar, A.
    Brentjens, M.
    Fallows, R. A.
    Frieswijk, W.
    Toribio, M. C.
    Adebahr, B.
    Arts, M.
    Bell, M. R.
    Bonafede, A.
    Bray, J.
    Broderick, J.
    Cantwell, T.
    Carroll, P.
    Cendes, Y.
    Clarke, A. O.
    Croston, J.
    Daiboo, S.
    de Gasperin, F.
    Gregson, J.
    Harwood, J.
    Hassall, T.
    Heesen, V.
    Horneffer, A.
    van der Horst, A. J.
    Iacobelli, M.
    Jelić, V.
    Jones, D.
    Kant, D.
    Kokotanekov, G.
    Martin, P.
    McKean, J. P.
    Morabito, L. K.
    Nikiel-Wroczy´nski, B.
    Offringa, A.
    Pandey, V. N.
    Pandey-Pommier, M.
    Pietka, M.
    Pratley, L.
    Riseley, C.
    Rowlinson, A.
    Sabater, J.
    Scaife, A. M. M.
    Scheers, L. H. A.
    Sendlinger, K.
    Shulevski, A.
    Sipior, M.
    Sobey, C.
    Stewart, A. J.
    Stroe, A.
    Swinbank, J.
    Tasse, C.
    Trüstedt, J.
    Varenius, E.
    van Velzen, S.
    Vilchez, N.
    van Weeren, R. J.
    Wijnholds, S.
    Williams, W. L.
    de Bruyn, A. G.
    Nijboer, R.
    Wise, M.
    Alexov, A.
    Anderson, J.
    Avruch, I. M.
    Beck, R.
    Bell, M. E.
    van Bemmel, I.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Breitling, F.
    Brouw, W. N.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    Conway, J. E.
    de Geus, E.
    de Jong, A.
    de Vos, M.
    Deller, A.
    Dettmar, R. -J
    Duscha, S.
    Eislöffel, J.
    Engels, D.
    Falcke, H.
    Fender, R.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Hamaker, J. P.
    Hessels, J. W. T.
    Hoeft, M.
    Hörandel, J.
    Holties, H. A.
    Intema, H.
    Jackson, N. J.
    Jütte, E.
    Karastergiou, A.
    Klijn, W. F. A.
    Kondratiev, V. I.
    Koopmans, L. V. E.
    Kuniyoshi, M.
    Kuper, G.
    Law, C.
    van Leeuwen, J.
    Loose, M.
    Maat, P.
    Markoff, S.
    McFadden, R.
    McKay-Bukowski, D.
    Mevius, M.
    Miller-Jones, J. C. A.
    Morganti, R.
    Munk, H.
    Nelles, A.
    Noordam, J. E.
    Norden, M. J.
    Paas, H.
    Polatidis, A. G.
    Reich, W.
    Renting, A.
    Röttgering, H.
    Schoenmakers, A.
    Schwarz, D.
    Sluman, J.
    Smirnov, O.
    Stappers, B. W.
    Steinmetz, M.
    Tagger, M.
    Tang, Y.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University, The Netherlands.
    Vermeulen, R.
    Vocks, C.
    Vogt, C.
    Wijers, R. A. M. J.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    The LOFAR Multifrequency Snapshot Sky Survey (MSSS): I. Survey description and first results2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 582, 1-22 p., A123Article in journal (Refereed)
    Abstract [en]

    We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky Low Frequency Array (LOFAR) imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS is exceptional due to its intrinsic multifrequency nature providing information about the spectral properties of the detected sources over more than two octaves (from 30 to 160 MHz). The broadband frequency coverage, together with the fast survey speed generated by LOFAR’s multibeaming capabilities, make MSSS the first survey of the sort anticipated to be carried out with the forthcoming Square Kilometre Array (SKA). Two of the sixteen frequency bands included in the survey were chosen to exactly overlap the frequency coverage of large-area Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) surveys at 74 MHz and 151 MHz respectively. The survey performance is illustrated within the MSSS Verification Field (MVF), a region of 100 square degrees centered at (α,δ)J2000 = (15h,69°). The MSSS results from the MVF are compared with previous radio survey catalogs. We assess the flux and astrometric uncertainties in the catalog, as well as the completeness and reliability considering our source finding strategy. We determine the 90% completeness levels within the MVF to be 100 mJy at 135 MHz with 108″ resolution, and 550 mJy at 50 MHz with 166″ resolution. Images and catalogs for the full survey, expected to contain 150 000–200 000 sources, will be released to a public web server. We outline the plans for the ongoing production of the final survey products, and the ultimate public release of images and source catalogs.

  • 19.
    Horandel, Jorg R.
    et al.
    Radboud Univ Nijmegen, Netherlands ; NIKHEF, Netherlands.
    Bonardi, A.
    Radboud Univ Nijmegen, Netherlands.
    Buitink, S.
    Radboud Univ Nijmegen, Netherlands ; Vrije Univ Brussel, Belgium.
    Corstanje, A.
    Radboud Univ Nijmegen, Netherlands.
    Falcke, H.
    Radboud Univ Nijmegen, Netherlands ; NIKHEF, Netherlands ; Max Planck Inst Radio Astron, Germany.
    Mitra, P.
    Vrije Univ Brussel, Belgium.
    Mulrey, K.
    Vrije Univ Brussel, Belgium.
    Nelles, A.
    Radboud Univ Nijmegen, Netherlands ; NIKHEF, Netherlands ; Univ Calif Irvine, USA.
    Rachen, J. P.
    Radboud Univ Nijmegen, Netherlands.
    Rossetto, L.
    Radboud Univ Nijmegen, Netherlands.
    Schellart, P.
    Radboud Univ Nijmegen, Netherlands ; Princeton Univ, USA.
    Scholten, O.
    Univ Groningen, Netherlands ; Vrije Univ Brussel, Belgium.
    ter Veen, S.
    ASTRON, Netherlands.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Radboud Univ Nijmegen, Netherlands.
    Trinh, T. N. G.
    Univ Groningen, Netherlands.
    Winchen, T.
    Vrije Univ Brussel, Belgium.
    The mass composition of cosmic rays measured with LOFAR2017In: RICAP16, 6TH ROMA INTERNATIONAL CONFERENCE ON ASTROPARTICLE PHYSICS / [ed] Morselli, A Capone, A Fernandez, GR, 2017, UNSP 02001Conference paper (Refereed)
    Abstract [en]

    High-energy cosmic rays, impinging on the atmosphere of the Earth initiate cascades of secondary particles, the extensive air showers. The electrons and positrons in the air shower emit electromagnetic radiation. This emission is detected with the LOFAR radio telescope in the frequency range from 30 to 240 MHz. The data are used to determine the properties of the incoming cosmic rays. The radio technique is now routinely used to measure the arrival direction, the energy, and the particle type (atomic mass) of cosmic rays in the energy range from 10(17) to 10(18) eV. This energy region is of particular astrophysical interest, since in this regime a transition from a Galactic to an extra-galactic origin of cosmic rays is expected. For illustration, the LOFAR results are used to set constraints on models to describe the origin of high-energy cosmic rays.

  • 20.
    Horneffer, A.
    et al.
    Radboud University Nijmegen, The Netherlands.
    Bähren, L.
    Radboud University Nijmegen, The Netherlands.
    Buitink, S.
    Radboud University Nijmegen, The Netherlands.
    Corstanje, A.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; ASTRON, The Netherlands.
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands.
    Lafebre, S.
    Radboud University Nijmegen, The Netherlands.
    Scholten, O.
    Kernfysisch Versneller Instituut, The Netherlands.
    Singh, K.
    Radboud University Nijmegen, The Netherlands ; Kernfysisch Versneller Instituut, The Netherlands.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Ter Veen, S.
    Radboud University Nijmegen, The Netherlands.
    Cosmic ray and neutrino measurements with LOFAR2010In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 617, no 1-3, 482-483 p.Article in journal (Refereed)
    Abstract [en]

    LOFAR is a new radio telescope being built in the Netherlands. It can detect cosmic particles by measuring radio pulses from air showers and by searching for radio pulses from particle cascades in the moon. The high density of radio antennas in the core and the excellent calibration will make LOFAR an unique tool to study the radio properties of single air showers and thus test and refine our theoretical understanding of the radio emission process in them. In addition LOFAR will be able to observe the moon with high sensitivity at low frequencies and search for particles interacting in the lunar regolith. This will give it unprecedented sensitivity to cosmic rays or neutrinos at energies around 1022eV. Triggering for both detection methods means detecting a short radio pulse and discriminating real events from radio interference. At LOFAR we will search for pulses in the digital data stream either from single antennas or from already beam-formed data and pick out real events from pulse form data. In addition we will have a small scintillator array to test and confirm the performance of the radio only trigger, and to provide additional measurements for the air shower reconstruction and analysis.

  • 21. Jelić, V.
    et al.
    de Bruyn, A. G.
    Mevius, M.
    Abdalla, F. B.
    Asad, K. M. B.
    Bernardi, G.
    Brentjens, M. A.
    Bus, S.
    Chapman, E.
    Ciardi, B.
    Daiboo, S.
    Fernandez, E. R.
    Ghosh, A.
    Harker, G.
    Jensen, H.
    Kazemi, S.
    Koopmans, L. V. E.
    Labropoulos, P.
    Martinez-Rubi, O.
    Mellema, G.
    Offringa, A. R.
    Pandey, V. N.
    Patil, A. H.
    Thomas, R. M.
    Vedantham, H. K.
    Veligatla, V.
    Yatawatta, S.
    Zaroubi, S.
    Alexov, A.
    Anderson, J.
    Avruch, I. M.
    Beck, R.
    Bell, M. E.
    Bentum, M. J.
    Best, P.
    Bonafede, A.
    Bregman, J.
    Breitling, F.
    Broderick, J.
    Brouw, W. N.
    Brüggen, M.
    Butcher, H. R.
    Conway, J. E.
    de Gasperin, F.
    de Geus, E.
    Deller, A.
    Dettmar, R. -J
    Duscha, S.
    Eislöffel, J.
    Engels, D.
    Falcke, H.
    Fallows, R. A.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Hamaker, J. P.
    Hassall, T. E.
    Haverkorn, M.
    Heald, G.
    Hessels, J. W. T.
    Hoeft, M.
    Hörandel, J.
    Horneffer, A.
    van der Horst, A.
    Iacobelli, M.
    Juette, E.
    Karastergiou, A.
    Kondratiev, V. I.
    Kramer, M.
    Kuniyoshi, M.
    Kuper, G.
    van Leeuwen, J.
    Maat, P.
    Mann, G.
    McKay-Bukowski, D.
    McKean, J. P.
    Munk, H.
    Nelles, A.
    Norden, M. J.
    Paas, H.
    Pandey-Pommier, M.
    Pietka, G.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Rowlinson, A.
    Scaife, A. M. M.
    Schwarz, D.
    Serylak, M.
    Smirnov, O.
    Steinmetz, M.
    Stewart, A.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, C.
    Vermeulen, R.
    Vocks, C.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wijnholds, S. J.
    Wucknitz, O.
    Zarka, P.
    Initial LOFAR observations of epoch of reionization windows: II. Diffuse polarized emission in the ELAIS-N1 field2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, 1-12 p., A101Article in journal (Refereed)
    Abstract [en]

    Aims. This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications for extracting of the cosmological 21 cm signal from the LOw-Frequency ARray – Epoch of Reionization (LOFAR-EoR) data.

    Methods. We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes.

    Results. The brightness temperature of the detected Galactic emission is on average ~4 K in polarized intensity and covers the range from –10 to + 13 rad m-2 in Faraday depth. The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to ≈1.5%. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies

    Conclusions. The wide frequency range, high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of ~1–2 rad m-2 in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%.

  • 22.
    Koul, R.
    et al.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Kaul, S. K.
    Bhabha Atomic Research Centre, India.
    Kaul, S. R.
    Bhabha Atomic Research Centre, India.
    Kumar, N.
    Bhabha Atomic Research Centre, India.
    Yadav, K. K.
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Chanchalani, K.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Chouhan, N.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Sahayanathan, S.
    Bhabha Atomic Research Centre, India.
    The TACTIC atmospheric Cherenkov imaging telescope2007In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 578, no 3, 548-564 p.Article in journal (Refereed)
    Abstract [en]

    The TACTIC (TeV Atomospheric Cherenkov Telescope with Imaging Camera) γγ-ray telescope, equipped with a light collector of area ∼9.5m2 and a medium resolution imaging camera of 349 pixels, has been in operation at Mt. Abu, India, since 2001. This paper describes the main features of its various subsystems and its overall performance with regard to (a) tracking accuracy of its two-axes drive system, (b) spot size of the light collector, (c) back-end signal processing electronics and topological trigger generation scheme, (d) data acquisition and control system and (e) relative and absolute gain calibration methodology. Using a trigger field-of-view of 11×1111×11 pixels (∼3.4×3.4)(∼3.4∘×3.4∘), the telescope records a cosmic ray event rate of ∼2.5Hz at a typical zenith angle of 1515∘. Monte Carlo simulation results are also presented in the paper for comparing the expected performance of the telescope with actual observational results. The consistent detection of a steady signal from the Crab Nebula above ∼1.2TeV energy, at a sensitivity level of ∼5.0σ∼5.0σ in ∼25h, alongwith excellent matching of its energy spectrum with that obtained by other groups, reassures that the performance of the TACTIC telescope is quite stable and reliable. Furthermore, encouraged by the detection of strong γγ-ray signals from Mrk 501 (during 1997 and 2006 observations) and Mrk 421 (during 2001 and 2005–2006 observations), we believe that there is considerable scope for the TACTIC telescope to monitor similar TeV γγ-ray emission activity from other active galactic nuclei on a long-term basis.

  • 23.
    Moldón, J.
    et al.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Deller, A. T.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Wucknitz, O.
    Max-Planck-Institut für Radioastronomie, Germany.
    Jackson, N.
    The University of Manchester, UK.
    Drabent, A.
    Thüringer Landessternwarte, Germany.
    Carozzi, T.
    Chalmers University of Technology.
    Conway, J.
    Chalmers University of Technology.
    Kapinska, A. D.
    University of Portsmouth, UK ; University of Sydney, Australia ; .
    McKean, J. P.
    ASTRON, the Netherlands Institute for Radio Astronomy, Nehterlands.
    Morabito, L.
    Leiden University, The Netherlands .
    Varenius, E.
    Chalmers University of Technology.
    Zarka, P.
    Univ. Paris-Diderot, France .
    Anderson, J.
    DeutschesGeoForschungsZentrum GFZ, Germany.
    Asgekar, A.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands ; ShellTechnology Center, India .
    Avruch, I. M.
    SRON Netherlands Insitute for Space Research, The Netherlands.
    Bell, M. E.
    CSIRO Australia Telescope National Facility, Australia .
    Bentum, M. J.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands ; University of Twente, The Netherlands .
    Bernardi, G.
    Harvard-Smithsonian Center for Astrophysics, USA.
    Best, P.
    University of Edinburgh, UK.
    Bîrzan, L.
    Leiden University, The Netherlands .
    Bregman, J.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Breitling, F.
    Leibniz-Institut für Astrophysik Potsdam, Germany.
    Broderick, J. W.
    University of Oxford, UK ; University of Southampton UK.
    Brüggen, M.
    University of Hamburg, Germany.
    Butcher, H. R.
    Australian National University, Australia .
    Carbone, D.
    University of Amsterdam, The Netherlands .
    Ciardi, B.
    Max Planck Institute for Astrophysics, Germany.
    de Gasperin, F.
    University of Hamburg, Germany.
    de Geus, E.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands ; SmarterVision BV, The Netherland .
    Duscha, S.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Eislöffel, J.
    Thüringer Landessternwarte, Germany.
    Engels, D.
    Hamburger Sternwarte, Germany.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Fallows, R. A.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Fender, R.
    University of Oxford, UK.
    Ferrari, C.
    Université de Nice Sophia-Antipolis, France.
    Frieswijk, W.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Garrett, M. A.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands ; Leiden University, The Netherlands .
    Grießmeier, J.
    LPC2E – Université d’Orléans/CNRS, France ; Univ. Orléans, France.
    Gunst, A. W.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Hamaker, J. P.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands.
    Hassall, T. E.
    University of Southampton, UK.
    Heald, G.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Hoeft, M.
    Thüringer Landessternwarte, Germany.
    Juette, E.
    Astronomisches Institut der Ruhr-Universität Bochum, Germany.
    Karastergiou, A.
    University of Oxford, UK.
    Kondratiev, V. I.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Kramer, M.
    Max-Planck-Institut für Radioastronomie, Germany ; The University of Manchester, UK.
    Kuniyoshi, M.
    Max-Planck-Institut für Radioastronomie, Germany.
    Kuper, G.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Maat, P.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Mann, G.
    Leibniz-Institut für Astrophysik Potsdam (AIP), Germany.
    Markoff, S.
    University of Amsterdam, The Netherlands .
    McFadden, R.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    McKay-Bukowski, D.
    University of Oulu, Finland ; STFC Rutherford Appleton Laboratory, UK.
    Morganti, R.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands ; Kapteyn Astronomical Institute, The Netherlands .
    Munk, H.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Norden, M. J.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Offringa, A. R.
    Australian National University, Australia.
    Orru, E.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Paas, H.
    University of Groningen, The Netherlands .
    Pandey-Pommier, M.
    Observatoire de Lyon, France.
    Pizzo, R.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Polatidis, A. G.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Reich, W.
    Max-Planck-Institut für Radioastronomie, Germany .
    Röttgering, H.
    Leiden University, The Netherlands .
    Rowlinson, A.
    CSIRO Australia Telescope National Facility, Australia .
    Scaife, A. M. M.
    University of Oxford, UK.
    Schwarz, D.
    Universität Bielefeld, Germany .
    Sluman, J.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Smirnov, O.
    Rhodes University, South Africa .
    Stappers, B. W.
    The University of Manchester, UK.
    Steinmetz, M.
    Leibniz-Institut für Astrophysik Potsdam (AIP), Germany .
    Tagger, M.
    LPC2E – Université d’Orléans/CNRS, France .
    Tang, Y.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Tasse, C.
    Observatoire de Paris, France.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands .
    Toribio, M. C.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Vermeulen, R.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Vocks, C.
    Leibniz-Institut für Astrophysik Potsdam (AIP), Germany .
    van Weeren, R. J.
    Harvard-Smithsonian Center for Astrophysics, USA.
    White, S.
    Max Planck Institute for Astrophysics, Germany.
    Wise, M. W.
    ASTRON, the Netherlands Institute for Radio Astronomy, Germany ; University of Amsterdam, The Netherlands .
    Yatawatta, S.
    ASTRON, the Netherlands Institute for Radio Astronomy, The Netherlands .
    Zensus, A.
    Max-Planck-Institut für Radioastronomie, Germany.
    The LOFAR long baseline snapshot calibrator survey2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 574, A73Article in journal (Refereed)
    Abstract [en]

    Aims. An efficient means of locating calibrator sources for international LOw Frequency ARray (LOFAR) is developed and used to determine the average density of usable calibrator sources on the sky for subarcsecond observations at 140 MHz.

    Methods. We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full international LOFAR array. Sources were preselected on the basis of 325 MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators.

    Results. More than 40% of the observed sources are detected on multiple baselines between international stations and 86 are classified as satisfactory calibrators. We show that a flat low-frequency spectrum (from 74 to 325 MHz) is the best predictor of compactness at 140 MHz. We extrapolate from our sample to show that the sky density of calibrators that are sufficiently bright to calibrate dispersive and non-dispersive delays for the international LOFAR using existing methods is 1.0 per square degree.

    Conclusions. The observed density of satisfactory delay calibrator sources means that observations with international LOFAR should be possible at virtually any point in the sky provided that a fast and efficient search, using the methodology described here, is conducted prior to the observation to identify the best calibrator.

  • 24. Morosan, D. E.
    et al.
    Gallagher, P. T.
    Zucca, P.
    Fallows, R.
    Carley, E. P.
    Mann, G.
    Bisi, M. M.
    Kerdraon, A.
    Konovalenko, A. A.
    MacKinnon, A. L.
    Rucker, H. O.
    Thidé, B.
    Magdalenić, J.
    Vocks, C.
    Reid, H.
    Anderson, J.
    Asgekar, A.
    Avruch, I. M.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bonafede, A.
    Bregman, J.
    Breitling, F.
    Broderick, J.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    Conway, J. E.
    de Gasperin, F.
    de Geus, E.
    Deller, A.
    Duscha, S.
    Eislöffel, J.
    Engels, D.
    Falcke, H.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Hassall, T. E.
    Hessels, J. W. T.
    Hoeft, M.
    Hörandel, J.
    Horneffer, A.
    Iacobelli, M.
    Juette, E.
    Karastergiou, A.
    Kondratiev, V. I.
    Kramer, M.
    Kuniyoshi, M.
    Kuper, G.
    Maat, P.
    Markoff, S.
    McKean, J. P.
    Mulcahy, D. D.
    Munk, H.
    Nelles, A.
    Norden, M. J.
    Orru, E.
    Paas, H.
    Pandey-Pommier, M.
    Pandey, V. N.
    Pietka, G.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Scaife, A. M. M.
    Schwarz, D.
    Serylak, M.
    Smirnov, O.
    Stappers, B. W.
    Stewart, A.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, C.
    Vermeulen, R.
    van Weeren, R. J.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    LOFAR tied-array imaging of Type III solar radio bursts2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, 1-8 p., A67Article in journal (Refereed)
    Abstract [en]

    Context. The Sun is an active source of radio emission which is often associated with energetic phenomena such as solar flares and coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), the Sun has not been imaged extensively because of the instrumental limitations of previous radio telescopes.

    Aims. Here, the combined high spatial, spectral, and temporal resolution of the LOw Frequency ARray (LOFAR) was used to study solar Type III radio bursts at 30–90 MHz and their association with CMEs.

    Methods. The Sun was imaged with 126 simultaneous tied-array beams within ≤5 R of the solar centre. This method offers benefits over standard interferometric imaging since each beam produces high temporal (~83 ms) and spectral resolution (12.5 kHz) dynamic spectra at an array of spatial locations centred on the Sun. LOFAR’s standard interferometric output is currently limited to one image per second.

    Results. Over a period of 30 min, multiple Type III radio bursts were observed, a number of which were found to be located at high altitudes (~4 R from the solar center at 30 MHz) and to have non-radial trajectories. These bursts occurred at altitudes in excess of values predicted by 1D radial electron density models. The non-radial high altitude Type III bursts were found to be associated with the expanding flank of a CME.

    Conclusions. The CME may have compressed neighbouring streamer plasma producing larger electron densities at high altitudes, while the non-radial burst trajectories can be explained by the deflection of radial magnetic fields as the CME expanded in the low corona.

  • 25. Nelles, A.
    et al.
    Buitink, S.
    Corstanje, A.
    Enriquez, J. E.
    Falcke, H.
    Hörandel, J. R.
    Rachen, J. P.
    Rossetto, L.
    Schellart, P.
    Scholten, O.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Trinh, T. N. G.
    The radio emission pattern of air showers as measured with LOFAR\mdasha tool for the reconstruction of the energy and the shower maximum2015In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The pattern of the radio emission of air showers is finely sampled with the Low-Frequency ARray (LOFAR). A set of 382 measured air showers is used to test a fast, analytic parameterization of the distribution of pulse powers. Using this parameterization we are able to reconstruct the shower axis and give estimators for the energy of the air shower as well as the distance to the shower maximum.

  • 26. Nelles, A.
    et al.
    Buitink, S.
    Corstanje, A.
    Enriquez, J. E.
    Falcke, H.
    Hörandel, J. R.
    Rachen, J. P.
    Schellart, P.
    Scholten, O.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud Unversity, The Netherlands.
    Trinh, T. N. G.
    A new way of air shower detection: measuring the properties of cosmic rays with LOFAR2015In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 632, no 1, 1-11 p.Article in journal (Refereed)
    Abstract [en]

    High-energy cosmic rays impinging onto the atmosphere of the Earth initiate cascades of secondary particles: extensive air showers. Many of the particles in a shower are electrons and positrons. During the development of the air shower and by interacting with the geomagnetic field, the electromagnetic cascade creates radiation, which we detect at frequencies of tens of MHz with the LOFAR radio telescope in the Netherlands. After many years of struggling to understand the emission mechanisms, the radio community has achieved the breakthrough. We are now able to determine direction, energy, and type of the shower- inducing primary particle from the radio measurements. The large number of antennas at LOFAR allows us to have a high precision and very detailed measurements. We will elaborate on the shower reconstruction, a precise description of the intensity of the radio signal at ground level (at frequencies from 10 to 240 MHz), a precise measurement of the shape of the radio wavefront, and on the reconstruction of the shower energy.

  • 27. Nelles, A.
    et al.
    Hörandel, J. R.
    Karskens, T.
    Krause, M.
    Buitink, S.
    Corstanje, A.
    Enriquez, J. E.
    Erdmann, M.
    Falcke, H.
    Haungs, A.
    Hiller, R.
    Huege, T.
    Krause, R.
    Link, K.
    Norden, M. J.
    Rachen, J. P.
    Rossetto, L.
    Schellart, P.
    Scholten, O.
    Schröder, F. G.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Trinh, T. N. G.
    Weidenhaupt, K.
    Wijnholds, S. J.
    Anderson, J.
    Bähren, L.
    Bell, M. E.
    Bentum, M. J.
    Best, P.
    Bonafede, A.
    Bregman, J.
    Brouw, W. N.
    Brüggen, M.
    Butcher, H. R.
    Carbone, D.
    Ciardi, B.
    de Gasperin, F.
    Duscha, S.
    Eislöffel, J.
    Fallows, R. A.
    Frieswijk, W.
    Garrett, M. A.
    van Haarlem, M. P.
    Heald, G.
    Hoeft, M.
    Horneffer, A.
    Iacobelli, M.
    Juette, E.
    Karastergiou, A.
    Kohler, J.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Kuper, G.
    van Leeuwen, J.
    Maat, P.
    McFadden, R.
    McKay-Bukowski, D.
    Orru, E.
    Paas, H.
    Pandey-Pommier, M.
    Pandey, V. N.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Schwarz, D.
    Serylak, M.
    Sluman, J.
    Smirnov, O.
    Tasse, C.
    Toribio, M. C.
    Vermeulen, R.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wucknitz, O.
    Zarka, P.
    Calibrating the absolute amplitude scale for air showers measured at LOFAR2015In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 10Article in journal (Refereed)
    Abstract [en]

    Air showers induced by cosmic rays create nanosecond pulses detectable at radio frequencies. These pulses have been measured successfully in the past few years at the LOw-Frequency ARray (LOFAR) and are used to study the properties of cosmic rays. For a complete understanding of this phenomenon and the underlying physical processes, an absolute calibration of the detecting antenna system is needed. We present three approaches that were used to check and improve the antenna model of LOFAR and to provide an absolute calibration of the whole system for air shower measurements. Two methods are based on calibrated reference sources and one on a calibration approach using the diffuse radio emission of the Galaxy, optimized for short data-sets. An accuracy of 19% in amplitude is reached. The absolute calibration is also compared to predictions from air shower simulations. These results are used to set an absolute energy scale for air shower measurements and can be used as a basis for an absolute scale for the measurement of astronomical transients with LOFAR.

  • 28. Nelles, A.
    et al.
    Schellart, P.
    Buitink, S.
    Corstanje, A.
    de Vries, K. D.
    Enriquez, J. E.
    Falcke, H.
    Frieswijk, W.
    Hörandel, J. R.
    Scholten, O.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    van den Akker, M.
    Anderson, J.
    Asgekar, A.
    Bell, M. E.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bregman, J.
    Breitling, F.
    Broderick, J.
    Brouw, W. N.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    Deller, A.
    Duscha, S.
    Eislöffel, J.
    Fallows, R. A.
    Garrett, M. A.
    Gunst, A. W.
    Hassall, T. E.
    Heald, G.
    Horneffer, A.
    Iacobelli, M.
    Juette, E.
    Karastergiou, A.
    Kondratiev, V. I.
    Kramer, M.
    Kuniyoshi, M.
    Kuper, G.
    Maat, P.
    Mann, G.
    Mevius, M.
    Norden, M. J.
    Paas, H.
    Pandey-Pommier, M.
    Pietka, G.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Scaife, A. M. M.
    Schwarz, D.
    Smirnov, O.
    Stappers, B. W.
    Steinmetz, M.
    Stewart, A.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Vermeulen, R.
    Vocks, C.
    van Weeren, R. J.
    Wijnholds, S. J.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    Measuring a Cherenkov ring in the radio emission from air showers at 110-190 MHz with LOFAR2015In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 65, 11-21 p.Article in journal (Refereed)
    Abstract [en]

    Measuring radio emission from air showers offers a novel way to determine properties of the primary cosmic rays such as their mass and energy. Theory predicts that relativistic time compression effects lead to a ring of amplified emission which starts to dominate the emission pattern for frequencies above ∼100∼100 MHz. In this article we present the first detailed measurements of this structure. Ring structures in the radio emission of air showers are measured with the LOFAR radio telescope in the frequency range of 110–190 MHz. These data are well described by CoREAS simulations. They clearly confirm the importance of including the index of refraction of air as a function of height. Furthermore, the presence of the Cherenkov ring offers the possibility for a geometrical measurement of the depth of shower maximum, which in turn depends on the mass of the primary particle.

  • 29.
    Nelles, Anna
    et al.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Buitink, Stijn
    University of Groningen, The Netherlands ; Radboud University Nijmegen, The Netherlands.
    Corstanje, Arthur
    Radboud University Nijmegen, The Netherlands.
    Enriquez, Emilio
    Radboud University Nijmegen, The Netherlands.
    Falcke, Heino
    Radboud University Nijmegen, The Netherlands ; Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Frieswijk, Wilfred
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Hörandel, Jörg
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Mevius, Maaijke
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; University of Groningen, The Netherlands.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Schellart, Pim
    Radboud University Nijmegen, The Netherlands.
    Scholten, Olaf
    University of Groningen, The Netherlands.
    Ter Veen, Sander
    Radboud University Nijmegen, The Netherlands.
    van den Akker, Martin
    Radboud University Nijmegen, The Netherlands.
    Detecting radio emission from air showers with LOFAR2013In: 5th International Workshop on Acoustic and Radio EeV Neutrino Detection Activities: ARENA 2012 / [ed] Robert Lahmann, Thomas Eberl, Kay Graf, Clancy James, Tim Huege, Timo Karg, Rolf Nahnhauer, American Institute of Physics (AIP), 2013, Vol. 1535, 105-110 p.Conference paper (Refereed)
    Abstract [en]

    LOFAR (the Low Frequency Array) is the largest radio telescope in the world for observing low frequency radio emission from 10 to 240 MHz. In addition to its use as an interferometric array, LOFAR is now routinely used to detect cosmic ray induced air showers by their radio emission. The LOFAR core in the Netherlands has a higher density of antennas than any dedicated cosmic ray experiment in radio. On an area of 12 km2 more than 2300 antennas are installed. They measure the radio emission from air showers with unprecedented precision and, therefore, give the perfect opportunity to disentangle the physical processes which cause the radio emission in air showers. In parallel to ongoing astronomical observations LOFAR is triggered by an array of particle detectors to record time-series containing cosmic-ray pulses. Cosmic rays have been measured with LOFAR since June 2011. We present the results of the first year of data.

  • 30. Oonk, J. B. R.
    et al.
    van Weeren, R. J.
    Salgado, F.
    Morabito, L. K.
    Tielens, A. G. G. M.
    Rottgering, H. J. A.
    Asgekar, A.
    White, G. J.
    Alexov, A.
    Anderson, J.
    Avruch, I. M.
    Batejat, F.
    Beck, R.
    Bell, M. E.
    van Bemmel, I.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bonafede, A.
    Breitling, F.
    Brentjens, M.
    Broderick, J.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    Conway, J. E.
    Corstanje, A.
    de Gasperin, F.
    de Geus, E.
    de Vos, M.
    Duscha, S.
    Eislöffel, J.
    Engels, D.
    van Enst, J.
    Falcke, H.
    Fallows, R. A.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J.
    Hamaker, J. P.
    Hassall, T. E.
    Heald, G.
    Hessels, J. W. T.
    Hoeft, M.
    Horneffer, A.
    van der Horst, A.
    Iacobelli, M.
    Jackson, N. J.
    Juette, E.
    Karastergiou, A.
    Klijn, W.
    Kohler, J.
    Kondratiev, V. I.
    Kramer, M.
    Kuniyoshi, M.
    Kuper, G.
    van Leeuwen, J.
    Maat, P.
    Macario, G.
    Mann, G.
    Markoff, S.
    McKean, J. P.
    Mevius, M.
    Miller-Jones, J. C. A.
    Mol, J. D.
    Mulcahy, D. D.
    Munk, H.
    Norden, M. J.
    Orru, E.
    Paas, H.
    Pandey-Pommier, M.
    Pandey, V. N.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Scaife, A. M. M.
    Schoenmakers, A.
    Schwarz, D.
    Shulevski, A.
    Sluman, J.
    Smirnov, O.
    Sobey, C.
    Stappers, B. W.
    Steinmetz, M.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Veen, S. t.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, C.
    van Nieuwpoort, R.
    Vermeulen, R.
    Vocks, C.
    Vogt, C.
    Wijers, R. A. M. J.
    Wise, M. W.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    Zensus, A.
    Discovery of carbon radio recombination lines in absorption towards Cygnus A2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 437, no 4, 3506-3515 p.Article in journal (Refereed)
    Abstract [en]

    We present the first detection of carbon radio recombination line absorption along the line of sight to Cygnus A. The observations were carried out with the Low Frequency Array in the 33–57 MHz range. These low-frequency radio observations provide us with a new line of sight to study the diffuse, neutral gas in our Galaxy. To our knowledge this is the first time that foreground Milky Way recombination line absorption has been observed against a bright extragalactic background source. By stacking 48 carbon α lines in the observed frequency range we detect carbon absorption with a signal-to-noise ratio of about 5. The average carbon absorption has a peak optical depth of 2 × 10−4, a line width of 10 km s−1 and a velocity of +4 km s−1 with respect to the local standard of rest. The associated gas is found to have an electron temperature Te ∼ 110 K and density ne ∼ 0.06 cm−3. These properties imply that the observed carbon α absorption likely arises in the cold neutral medium of the Orion arm of the Milky Way. Hydrogen and helium lines were not detected to a 3σ peak optical depth limit of 1.5 × 10−4 for a 4 km s−1 channel width. Radio recombination lines associated with Cygnus A itself were also searched for, but are not detected. We set a 3σ upper limit of 1.5 × 10−4 for the peak optical depth of these lines for a 4 km s−1 channel width.

  • 31. Orrù, E.
    et al.
    van Velzen, S.
    Pizzo, R. F.
    Yatawatta, S.
    Paladino, R.
    Iacobelli, M.
    Murgia, M.
    Falcke, H.
    Morganti, R.
    de Bruyn, A. G.
    Ferrari, C.
    Anderson, J.
    Bonafede, A.
    Mulcahy, D.
    Asgekar, A.
    Avruch, I. M.
    Beck, R.
    Bell, M. E.
    van Bemmel, I.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Breitling, F.
    Broderick, J. W.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    Conway, J. E.
    Corstanje, A.
    de Geus, E.
    Deller, A.
    Duscha, S.
    Eislöffel, J.
    Engels, D.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Hamaker, J. P.
    Heald, G.
    Hoeft, M.
    van der Horst, A. J.
    Intema, H.
    Juette, E.
    Kohler, J.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Kuper, G.
    Loose, M.
    Maat, P.
    Mann, G.
    Markoff, S.
    McFadden, R.
    McKay-Bukowski, D.
    Miley, G.
    Moldon, J.
    Molenaar, G.
    Munk, H.
    Nelles, A.
    Paas, H.
    Pandey-Pommier, M.
    Pandey, V. N.
    Pietka, G.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Rowlinson, A.
    Scaife, A.
    Schoenmakers, A.
    Schwarz, D.
    Serylak, M.
    Shulevski, A.
    Smirnov, O.
    Steinmetz, M.
    Stewart, A.
    Swinbank, J.
    Tagger, M.
    Tasse, C.
    Thoudam, Satyendra
    Radboud University, The Netherlands.
    Toribio, M. C.
    Vermeulen, R.
    Vocks, C.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wise, M. W.
    Wucknitz, O.
    Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620: A fresh view on a restarted AGN and doubeltjes2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 584, 1-12 p., A112Article in journal (Refereed)
    Abstract [en]

    Context. The existence of double-double radio galaxies (DDRGs) is evidence for recurrent jet activity in active galactic nuclei (AGN), as expected from standard accretion models. A detailed study of these rare sources provides new perspectives for investigating the AGN duty cycle, AGN-galaxy feedback, and accretion mechanisms. Large catalogues of radio sources, on the other hand, provide statistical information about the evolution of the radio-loud AGN population out to high redshifts.

    Aims. Using wide-field imaging with the LOFAR telescope, we study both a well-known DDRG as well as a large number of radio sources in the field of view.

    Methods. We present a high resolution image of the DDRG B1834+620 obtained at 144 MHz using LOFAR commissioning data. Our image covers about 100 square degrees and contains over 1000 sources.

    Results. The four components of the DDRG B1834+620 have been resolved for the first time at 144 MHz. Inner lobes were found to point towards the direction of the outer lobes, unlike standard FR II sources. Polarized emission was detected at +60 rad m-2 in the northern outer lobe. The high spatial resolution allows the identification of a large number of small double-lobed radio sources; roughly 10% of all sources in the field are doubles with a separation smaller than 1′.

    Conclusions. The spectral fit of the four components is consistent with a scenario in which the outer lobes are still active or the jets recently switched off, while emission of the inner lobes is the result of a mix-up of new and old jet activity. From the presence of the newly extended features in the inner lobes of the DDRG, we can infer that the mechanism responsible for their formation is the bow shock that is driven by the newly launched jet. We find that the density of the small doubles exceeds the density of FR II sources with similar properties at 1.4 GHz, but this difference becomes smaller for low flux densities. Finally, we show that the significant challenges of wide-field imaging (e.g., time and frequency variation of the beam, directional dependent calibration errors) can be solved using LOFAR commissioning data, thus demonstrating the potential of the full LOFAR telescope to discover millions of powerful AGN at redshift z ~ 1.

  • 32.
    Pilia, M.
    et al.
    ASTRON, The Netherlands ; Osservatorio Astronomico di Cagliari INAF-OAC, Italy.
    Hessels, J. W. T.
    ASTRON, The Netherlands ; University of Amsterdam, The Netherlands.
    Stappers, B. W.
    The University of Manchester, UK.
    Kondratiev, V. I.
    ASTRON, The Netherlands ; Lebedev Physical Institute, Russia.
    Kramer, M.
    Max Planck Institute for Radio Astronomy, Germany ; The University of Manchester, UK.
    van Leeuwen, J.
    ASTRON, The Netherlands ; University of Amsterdam, The Netherlands.
    Weltevrede, P.
    The University of Manchester, UK.
    Lyne, A. G.
    The University of Manchester, UK.
    Zagkouris, K.
    University of Oxford, UK.
    Hassall, T. E.
    University of Southampton, UK.
    Bilous, A. V.
    Breton, R. P.
    Falcke, H.
    Grießmeier, J. -M
    Keane, E.
    Karastergiou, A.
    Kuniyoshi, M.
    Noutsos, A.
    Os\lowski, S.
    Serylak, M.
    Sobey, C.
    ter Veen, S.
    Alexov, A.
    Anderson, J.
    Asgekar, A.
    Avruch, I. M.
    Bell, M. E.
    Bentum, M. J.
    Bernardi, G.
    Bîrzan, L.
    Bonafede, A.
    Breitling, F.
    Broderick, J. W.
    Brüggen, M.
    Ciardi, B.
    Corbel, S.
    de Geus, E.
    de Jong, A.
    Deller, A.
    Duscha, S.
    Eislöffel, J.
    Fallows, R. A.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Gunst, A. W.
    Hamaker, J. P.
    Heald, G.
    Horneffer, A.
    Jonker, P.
    Juette, E.
    Kuper, G.
    Maat, P.
    Mann, G.
    Markoff, S.
    McFadden, R.
    McKay-Bukowski, D.
    Miller-Jones, J. C. A.
    Nelles, A.
    Paas, H.
    Pandey-Pommier, M.
    Pietka, M.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Rowlinson, A.
    Schwarz, D.
    Smirnov, O.
    Steinmetz, M.
    Stewart, A.
    Swinbank, J. D.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, M. C.
    van der Horst, A. J.
    Vermeulen, R.
    Vocks, C.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wijnands, R.
    Wijnholds, S. J.
    Wucknitz, O.
    Zarka, P.
    Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 586, A92Article in journal (Refereed)
    Abstract [en]

    Context. LOFAR offers the unique capability of observing pulsars across the 10−240  MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively.

    Aims. The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium.

    Methods. We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: high band (120–167 MHz, 100 profiles) and low band (15–62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and 1400 MHz) to study the profile evolution. The profiles were aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR.

    Results. We find that the profile evolution with decreasing radio frequency does not follow a specific trend; depending on the geometry of the pulsar, new components can enter into or be hidden from view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories.

  • 33.
    Rannot, R. C.
    et al.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Yadav, K.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Godambe, S.
    Bhabha Atomic Research Centre, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Sahayanathan, S.
    Bhabha Atomic Research Centre, India.
    Sapru, M. L.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    TeV gamma-ray Observations of the Blazar Markarian 421 from January to April 2004 with TACTIC Imaging Element2005In: 29th International Cosmic Ray Conference Pune (2005), 2005, Vol. 4, 355-358 p.Conference paper (Refereed)
    Abstract [en]

    We have observed the blazar Markarian 421 (z=0.031 ) with the TACTIC gamma- ray telescope having thresholdenergy of 1.5TeV at Mt. Abu Rajasthan India from January to April 2004. Observations were made intracking mode for a total of 84(on) /16 (off-source) hours with its imaging element equipped with a 349- pixelPMTs camera. During this period, we nd an evidence of a TeV gamma-ray signal with a statistical signi-cance of 6.8. The differential energy spectrum derived in the energy range 2 - 9 TeV is well represented bya simple power law, with a differential spectral index of 2.800.20.

  • 34.
    Rossetto, L.
    et al.
    Radboud Univ Nijmegen, Netherlands.
    Buitink, S.
    Vrije Univ Brussel, Belgium.
    Corstanje, A.
    Radboud Univ Nijmegen, Netherlands.
    Enriquez, J. E.
    Radboud Univ Nijmegen, Netherlands.
    Falcke, H.
    Radboud Univ Nijmegen, Netherlands ; NIKHEF, Netherlands ; Netherlands Inst Radio Astron ASTRON, Netherlands.
    Horandel, J. R.
    Radboud Univ Nijmegen, Netherlands ; NIKHEF, Netherlands.
    Nelles, A.
    Univ Calif Irvine, USA.
    Rachen, J. P.
    Radboud Univ Nijmegen, Netherlands.
    Schellart, P.
    Radboud Univ Nijmegen, Netherlands.
    Scholten, O.
    Univ Groningen, Netherlands ; Vrije Univ Brussel, Belgium.
    ter Veen, S.
    Radboud Univ Nijmegen, Netherlands ; Netherlands Inst Radio Astron ASTRON, Netherlands.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Trinh, T. N. G.
    Univ Groningen, Netherlands.
    Measurement of cosmic rays with LOFAR2016In: XIV INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS (TAUP 2015), PTS 1-7, Institute of Physics Publishing (IOPP), 2016, UNSP 052035Conference paper (Refereed)
    Abstract [en]

    The LOw Frequency ARay (LOFAR) is a multipurpose radio -antenna array aimed to detect radio signals in the 10 - 240 MHz frequency range, covering a large surface in Northern Europe with a higher density in the Northern Netherlands. Radio emission in the atmosphere is produced by cosmic -ray induced air showers through the interaction of charged particles with the Earth magnetic field. The detection of radio signals allows to reconstruct several properties of the observed cascade. We review here all important results achieved in the last years. We proved that the radio -signal distribution at ground level is described by a two-dimensional pattern, which is well fitted by a double Gaussian function. The radio -signal arrival time and polarization have been measured, thus providing additional information on the extensive air shower geometry, and on the radio emission processes. We also showed that the radio signal reaches ground in a thin, curved wavefront which is best parametrized by a hyperboloid shape centred around the shower axis. Radio emission has also been studied under thunderstorm conditions and compared to fair weather conditions. Moreover, by using a hybrid reconstruction technique, we performed mass composition measurements in the energy range 10(17) - 10(18) eV.

  • 35.
    Sapru, M. L.
    et al.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Threshold energy estimate of the proposed MACE gamma-ray telescope at Hanle2005In: 29th International Cosmic Ray Conference Pune (2005), 2005, Vol. 5, 263-266 p.Conference paper (Refereed)
    Abstract [en]

    The fact that EGRET detected over 250 objects above 100 MeV while only a handful of sources have beendetected above 100 GeV indicates that there is a good chance of detecting a signicant number of these sources(particularly those which do not show a signature of steepening or cut off up to a few GeV), if the thresholdenergy of ground based telescopes is lowered to20 GeV. In the present study, we report the threshold energyestimate of the MACE (Major Atmospheric Cerenkov Experiment) imaging telescope, proposed to be installedin the campus of Indian Astronomical Observatory at Hanle (32.8N, 78.9E, 4200m asl). The results ofthe Monte Carlo simulations carried out with CORSIKA code, suggest that using a pixel threshold of4peand a nearest neighbour quadruplet trigger,-ray energy threshold of15GeV is achievable by the MACEtelescope. Details of the simulation work for estimating the threshold energy along with results obtained arepresented in this paper.

  • 36.
    Schellart, P.
    et al.
    Radboud University Nijmegen, The Netherlands.
    Buitink, S.
    Radboud University Nijmegen, The Netherlands ; University Groningen, The Netherlands.
    Corstanje, A.
    Radboud University Nijmegen, The Netherlands.
    Enriquez, J. E.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands ; Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; Max-Planck-Institut für Radioastronomie, Germany.
    Frieswijk, W.
    Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands.
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Krause, M.
    Radboud University Nijmegen, The Netherlands.
    Nelles, A.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Scholten, O.
    University Groningen, The Netherlands.
    ter Veen, S.
    Radboud University Nijmegen, The Netherlands.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    van den Akker, M.
    Radboud University Nijmegen, The Netherlands.
    Recent results from cosmic-ray measurements with LOFAR2014In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 742, 115-118 p.Article in journal (Refereed)
    Abstract [en]

    LOFAR, the Low Frequency Array, is currently the world's largest distributed radio telescope observing at frequencies below 240 MHz. LOFAR is measuring cosmic-ray induced air-showers since June 2011 and has collected several hundreds of events with hundreds of antennas per individual event. We present measurements of the radio signal strength as well as high-precision measurements of wavefront curvature and polarization. These will enable us to disentangle the different emission mechanisms at play, such as geomagnetic radiation, charge excess, and Askaryan or Cherenkov effects, leading to a full understanding of the air-shower radio emission. Furthermore we give a first example on how the full complexity of the signal enables radio measurements to be used to study primary particle composition.

  • 37.
    Schellart, P.
    et al.
    Radboud University Nijmegen, The Netherlands.
    Buitink, S.
    Radboud University Nijmegen, The Netherlands.
    Corstanje, A.
    Radboud University Nijmegen, The Netherlands.
    Enriquez, J. E.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands ; Netherlands Institute for Radio Astronomy (ASTRON), The Netherlands ; Max Planck Institute for Radio Astronomy, Germany.
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Krause, M.
    Radboud University Nijmegen, The Netherlands ; Deutsches Elektronen-Synchrotron (DESY), Germany.
    Nelles, A.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Rachen, J. P.
    Radboud University Nijmegen, The Netherlands.
    Scholten, O.
    University of Groningen, The Netherlands.
    ter Veen, S.
    Radboud University Nijmegen, The Netherlands.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Trinh, T. N. G.
    University of Groningen, The Netherlands.
    Polarized radio emission from extensive air showers measured with LOFAR2014In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 10Article in journal (Refereed)
    Abstract [en]

    We present LOFAR measurements of radio emission from extensive air showers. We find that this emission is strongly polarized, with a median degree of polarization of nearly

    99%, and that the angle between the polarization direction of the electric field and the Lorentz force acting on the particles, depends on the observer location in the shower plane. This can be understood as a superposition of the radially polarized charge-excess emission mechanism, first proposed by Askaryan and the geomagnetic emission mechanism proposed by Kahn and Lerche. We calculate the relative strengths of both contributions, as quantified by the charge-excess fraction, for 163 individual air showers. We find that the measured charge-excess fraction is higher for air showers arriving from closer to the zenith. Furthermore, the measured charge-excess fraction also increases with increasing observer distance from the air shower symmetry axis. The measured values range from (3.3± 1.0)% for very inclined air showers at 25 m to (20.3± 1.3)% for almost vertical showers at 225 m. Both dependencies are in qualitative agreement with theoretical predictions.

  • 38. Schellart, P.
    et al.
    Nelles, A.
    Buitink, S.
    Corstanje, A.
    Enriquez, J. E.
    Falcke, H.
    Frieswijk, W.
    Hörandel, J. R.
    Horneffer, A.
    James, C. W.
    Krause, M.
    Mevius, M.
    Scholten, O.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    van den Akker, M.
    Alexov, A.
    Anderson, J.
    Avruch, I. M.
    Bähren, L.
    Beck, R.
    Bell, M. E.
    Bennema, P.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bregman, J.
    Breitling, F.
    Brentjens, M.
    Broderick, J.
    Brüggen, M.
    Ciardi, B.
    Coolen, A.
    de Gasperin, F.
    de Geus, E.
    de Jong, A.
    de Vos, M.
    Duscha, S.
    Eislöffel, J.
    Fallows, R. A.
    Ferrari, C.
    Garrett, M. A.
    Grießmeier, J.
    Grit, T.
    Hamaker, J. P.
    Hassall, T. E.
    Heald, G.
    Hessels, J. W. T.
    Hoeft, M.
    Holties, H. A.
    Iacobelli, M.
    Juette, E.
    Karastergiou, A.
    Klijn, W.
    Kohler, J.
    Kondratiev, V. I.
    Kramer, M.
    Kuniyoshi, M.
    Kuper, G.
    Maat, P.
    Macario, G.
    Mann, G.
    Markoff, S.
    McKay-Bukowski, D.
    McKean, J. P.
    Miller-Jones, J. C. A.
    Mol, J. D.
    Mulcahy, D. D.
    Munk, H.
    Nijboer, R.
    Norden, M. J.
    Orru, E.
    Overeem, R.
    Paas, H.
    Pandey-Pommier, M.
    Pizzo, R.
    Polatidis, A. G.
    Renting, A.
    Romein, J. W.
    Röttgering, H.
    Schoenmakers, A.
    Schwarz, D.
    Sluman, J.
    Smirnov, O.
    Sobey, C.
    Stappers, B. W.
    Steinmetz, M.
    Swinbank, J.
    Tang, Y.
    Tasse, C.
    Toribio, C.
    van Leeuwen, J.
    van Nieuwpoort, R.
    van Weeren, R. J.
    Vermaas, N.
    Vermeulen, R.
    Vocks, C.
    Vogt, C.
    Wijers, R. A. M. J.
    Wijnholds, S. J.
    Wise, M. W.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    Zensus, A.
    Detecting cosmic rays with the LOFAR radio telescope2013In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 560, 1-14 p., A98Article in journal (Refereed)
    Abstract [en]

    The low frequency array (LOFAR), is the first radio telescope designed with the capability to measure radio emission from cosmic-ray induced air showers in parallel with interferometric observations. In the first ~2 years of observing, 405 cosmic-ray events in the energy range of 1016−1018 eV have been detected in the band from 30−80 MHz. Each of these air showers is registered with up to ~1000 independent antennas resulting in measurements of the radio emission with unprecedented detail. This article describes the dataset, as well as the analysis pipeline, and serves as a reference for future papers based on these data. All steps necessary to achieve a full reconstruction of the electric field at every antenna position are explained, including removal of radio frequency interference, correcting for the antenna response and identification of the pulsed signal.

  • 39. Schellart, P.
    et al.
    Trinh, T. N. G.
    Buitink, S.
    Corstanje, A.
    Enriquez, J. E.
    Falcke, H.
    Hörandel, J. R.
    Nelles, A.
    Rachen, J. P.
    Rossetto, L.
    Scholten, O.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Ebert, U.
    Koehn, C.
    Rutjes, C.
    Alexov, A.
    Anderson, J. M.
    Avruch, I. M.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bonafede, A.
    Breitling, F.
    Broderick, J. W.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    de Geus, E.
    de Vos, M.
    Duscha, S.
    Eislöffel, J.
    Fallows, R. A.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Heald, G.
    Hessels, J. W. T.
    Hoeft, M.
    Holties, H. A.
    Juette, E.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Kuper, G.
    Mann, G.
    McFadden, R.
    McKay-Bukowski, D.
    McKean, J. P.
    Mevius, M.
    Moldon, J.
    Norden, M. J.
    Orru, E.
    Paas, H.
    Pandey-Pommier, M.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Röttgering, H.
    Scaife, A. M. M.
    Schwarz, D. J.
    Serylak, M.
    Smirnov, O.
    Steinmetz, M.
    Swinbank, J.
    Tagger, M.
    Tasse, C.
    Toribio, M. C.
    van Weeren, R. J.
    Vermeulen, R.
    Vocks, C.
    Wise, M. W.
    Wucknitz, O.
    Zarka, P.
    Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air Showers2015In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, no 16, 1-5 p., 165001Article in journal (Refereed)
    Abstract [en]

    We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electric fields.

  • 40.
    Scholten, O.
    et al.
    Univ Groningen, Netherlands ; Vrije Univ Brussel, Belgium.
    Trinh, T. N. G.
    Univ Groningen, Netherlands.
    Bonardi, A.
    Radboud Univ Nijmegen, Netherlands.
    Buitink, S.
    Vrije Univ Brussel, Belgium.
    Correa, P.
    Vrije Univ Brussel, Belgium.
    Corstanje, A.
    Radboud Univ Nijmegen, Netherlands.
    Hasankiadeh, Q. Dorosti
    Univ Groningen, Netherlands.
    Falcke, H.
    Radboud Univ Nijmegen, Netherlands ; Nikhef, Netherlands ; Netherlands Inst Radio Astron ASTRON, Netherlands ; Max Planck Inst Radioastron, Germany.
    Horandel, J. R.
    Radboud Univ Nijmegen, Netherlands ; Nikhef, Netherlands.
    Mitra, P.
    Vrije Univ Brussel, Belgium.
    Mulrey, K.
    Vrije Univ Brussel, Belgium.
    Nelles, A.
    Radboud Univ Nijmegen, Netherlands ; Univ Calif Irvine, USA.
    Rachen, J. P.
    Radboud Univ Nijmegen, Netherlands.
    Rossetto, L.
    Radboud Univ Nijmegen, Netherlands.
    Schellart, P.
    Radboud Univ Nijmegen, Netherlands ; Princeton Univ, USA.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Radboud Univ Nijmegen, Netherlands.
    ter Veen, S.
    Radboud Univ Nijmegen, Netherlands ; Netherlands Inst Radio Astron ASTRON, Netherlands.
    de Vries, K. D.
    Vrije Univ Brussel, Belgium.
    Winchen, T.
    Vrije Univ Brussel, Belgium.
    Measurement of the circular polarization in radio emission from extensive air showers confirms emission mechanisms2016In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 94, no 10, 103010Article in journal (Refereed)
    Abstract [en]

    We report here on a novel analysis of the complete set of four Stokes parameters that uniquely determine the linear and/or circular polarization of the radio signal for an extensive air shower. The observed dependency of the circular polarization on azimuth angle and distance to the shower axis is a clear signature of the interfering contributions from two different radiation mechanisms, a main contribution due to a geomagnetically-induced transverse current and a secondary component due to the build-up of excess charge at the shower front. The data, as measured at LOFAR, agree very well with a calculation from first principles. This opens the possibility to use circular polarization as an investigative tool in the analysis of air shower structure, such as for the determination of atmospheric electric fields.

  • 41.
    Scholten, Olaf
    et al.
    Univ Groningen, Netherlands ; Vrije Univ Brussel, Belgium.
    Bonardi, Antonio
    Radboud Univ Nijmegen, Netherlands.
    Buitink, Stijn
    Vrije Univ Brussel, Belgium.
    Corstanje, Arthur
    Radboud Univ Nijmegen, Netherlands.
    Ebert, Ute
    Ctr Wiskunde & Informat, Netherlands ; Eindhoven Univ Technol, Netherlands.
    Falcke, Heino
    Netherlands Inst Radio Astron ASTRON, Netherlands ; Radboud Univ Nijmegen, Netherlands.
    Horandel, Jorg
    Radboud Univ Nijmegen, Netherlands.
    Mitra, Pragati
    Vrije Univ Brussel, Belgium.
    Mulrey, Katharine
    Vrije Univ Brussel, Belgium.
    Nelles, Anna
    Univ Calif Irvine, USA.
    Rachen, Jorg
    Radboud Univ Nijmegen, Netherlands.
    Rossetto, Laura
    Radboud Univ Nijmegen, Netherlands.
    Rutjes, Casper
    Ctr Wiskunde & Informat, Amsterdam, Netherlands..
    Schellart, Pim
    Princeton Univ, USA.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Trinh, Gia
    Univ Groningen, Netherlands.
    ter Veen, Sander
    Univ Groningen, Netherlands.
    Winchen, Tobias
    Vrije Univ Brussel, Belgium.
    Precision study of radio emission from air showers at LOFAR2017In: RICAP16, 6TH ROMA INTERNATIONAL CONFERENCE ON ASTROPARTICLE PHYSICS / [ed] Morselli, A Capone, A Fernandez, GR, 2017, UNSP 02012Conference paper (Refereed)
    Abstract [en]

    Radio detection as well as modeling of cosmic rays has made enormous progress in the past years. We show this by using the subtle circular polarization of the radio pulse from air showers measured in fair weather conditions and the intensity of radio emission from an air shower under thunderstorm conditions.

  • 42. Shulevski, A.
    et al.
    Morganti, R.
    Barthel, P. D.
    Murgia, M.
    van Weeren, R. J.
    White, G. J.
    Brüggen, M.
    Kunert-Bajraszewska, M.
    Jamrozy, M.
    Best, P. N.
    Röttgering, H. J. A.
    Chyzy, K. T.
    de Gasperin, F.
    Bîrzan, L.
    Brunetti, G.
    Brienza, M.
    Rafferty, D. A.
    Anderson, J.
    Beck, R.
    Deller, A.
    Zarka, P.
    Schwarz, D.
    Mahony, E.
    Orrú, E.
    Bell, M. E.
    Bentum, M. J.
    Bernardi, G.
    Bonafede, A.
    Breitling, F.
    Broderick, J. W.
    Butcher, H. R.
    Carbone, D.
    Ciardi, B.
    de Geus, E.
    Duscha, S.
    Eislöffel, J.
    Engels, D.
    Falcke, H.
    Fallows, R. A.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Heald, G.
    Hoeft, M.
    Hörandel, J.
    Horneffer, A.
    van der Horst, A. J.
    Intema, H.
    Juette, E.
    Karastergiou, A.
    Kondratiev, V. I.
    Kramer, M.
    Kuniyoshi, M.
    Kuper, G.
    Maat, P.
    Mann, G.
    McFadden, R.
    McKay-Bukowski, D.
    McKean, J. P.
    Meulman, H.
    Mulcahy, D. D.
    Munk, H.
    Norden, M. J.
    Paas, H.
    Pandey-Pommier, M.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Rowlinson, A.
    Scaife, A. M. M.
    Serylak, M.
    Sluman, J.
    Smirnov, O.
    Steinmetz, M.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, M. C.
    Vermeulen, R.
    Vocks, C.
    Wijers, R. A. M. J.
    Wise, M. W.
    Wucknitz, O.
    The peculiar radio galaxy 4C 35.06: a case for recurrent AGN activity?2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 579, 1-10 p., A27Article in journal (Refereed)
    Abstract [en]

    Using observations obtained with the LOw Fequency ARray (LOFAR), the Westerbork Synthesis Radio Telescope (WSRT) and archival Very Large Array (VLA) data, we have traced the radio emission to large scales in the complex source 4C 35.06 located in the core of the galaxy cluster Abell 407. At higher spatial resolution (~ 4″), the source was known to have two inner radio lobes spanning 31 kpc and a diffuse, low-brightness extension running parallel to them, offset by about 11 kpc (in projection). At 62 MHz, we detect the radio emission of this structure extending out to 210 kpc. At 1.4 GHz and intermediate spatial resolution (~ 30″), the structure appears to have a helical morphology. We have derived the characteristics of the radio spectral index across the source. We show that the source morphology is most likely the result of at least two episodes of AGN activity separated by a dormant period of around 35 Myr. The outermost regions of radio emission have a steep spectral index (α< − 1), indicative of old plasma. We connect the spectral index properties of the resolved source structure with the integrated fluxdensity spectral index of 4C 35.06 and suggest an explanation for its unusual integrated flux density spectral shape (a moderately steep power law with no discernible spectral break), possibly providing a proxy for future studies of more distant radio sources through inferring their detailed spectral index properties and activity history from their integrated spectral indices. The AGN is hosted by one of the galaxies located in the cluster core of Abell 407. We propose that it is intermittently active as it moves in the dense environment in the cluster core. In this scenario, the AGN turned on sometime in the past, and has produced the helical pattern of emission, possibly a sign of jet precession/merger during that episode of activity. Using LOFAR, we can trace the relic plasma from that episode of activity out to greater distances from the core than ever before. Using the the WSRT, we detect H I in absorption against the center of the radio source. The absorption profile is relatively broad (FWHM of 288 kms-1), similar to what is found in other clusters. The derived column density is NHI ~ 4 × 1020 cm-2 for a Tspin = 100 K. This detection supports the connection – already suggested for other restarted radio sources – between the presence of cold gas and restarting activity. The cold gas appears to be dominated by a blue-shifted component although the broad H I profile could also include gas with different kinematics. Understanding the duty cycle of the radio emission as well as the triggering mechanism for starting (or restarting) the radio-loud activity can provide important constraints to quantify the impact of AGN feedback on galaxy evolution. The study of these mechanisms at low frequencies using morphological and spectral information promises to bring new important insights in this field.

  • 43. Sobey, C.
    et al.
    Young, N. J.
    Hessels, J. W. T.
    Weltevrede, P.
    Noutsos, A.
    Stappers, B. W.
    Kramer, M.
    Bassa, C.
    Lyne, A. G.
    Kondratiev, V. I.
    Hassall, T. E.
    Keane, E. F.
    Bilous, A. V.
    Breton, R. P.
    Grießmeier, J. -M
    Karastergiou, A.
    Pilia, M.
    Serylak, M.
    Veen, S. t.
    van Leeuwen, J.
    Alexov, A.
    Anderson, J.
    Asgekar, A.
    Avruch, I. M.
    Bell, M. E.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bîrzan, L.
    Bonafede, A.
    Breitling, F.
    Broderick, J.
    Brüggen, M.
    Corstanje, A.
    Carbone, D.
    de Geus, E.
    de Vos, M.
    van Duin, A.
    Duscha, S.
    Eislöffel, J.
    Falcke, H.
    Fallows, R. A.
    Fender, R.
    Ferrari, C.
    Frieswijk, W.
    Garrett, M. A.
    Gunst, A. W.
    Hamaker, J. P.
    Heald, G.
    Hoeft, M.
    Hörandel, J.
    Jütte, E.
    Kuper, G.
    Maat, P.
    Mann, G.
    Markoff, S.
    McFadden, R.
    McKay-Bukowski, D.
    McKean, J. P.
    Mulcahy, D. D.
    Munk, H.
    Nelles, A.
    Norden, M. J.
    Orrù, E.
    Paas, H.
    Pandey-Pommier, M.
    Pandey, V. N.
    Pietka, G.
    Pizzo, R.
    Polatidis, A. G.
    Rafferty, D.
    Renting, A.
    Röttgering, H.
    Rowlinson, A.
    Scaife, A. M. M.
    Schwarz, D.
    Sluman, J.
    Smirnov, O.
    Steinmetz, M.
    Stewart, A.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, C.
    Vermeulen, R.
    Vocks, C.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wise, M. W.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    LOFAR discovery of a quiet emission mode in PSR B0823+262015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 451, 2493-2506 p.Article in journal (Refereed)
    Abstract [en]

    PSR B0823+26, a 0.53-s radio pulsar, displays a host of emission phenomena over time-scales of seconds to (at least) hours, including nulling, subpulse drifting, and mode-changing. Studying pulsars like PSR B0823+26 provides further insight into the relationship between these various emission phenomena and what they might teach us about pulsar magnetospheres. Here we report on the LOFAR (Low-Frequency Array) discovery that PSR B0823+26 has a weak and sporadically emitting ‘quiet’ (Q) emission mode that is over 100 times weaker (on average) and has a nulling fraction forty-times greater than that of the more regularly-emitting ‘bright’ (B) mode. Previously, the pulsar has been undetected in the Q mode, and was assumed to be nulling continuously. PSR B0823+26 shows a further decrease in average flux just before the transition into the B mode, and perhaps truly turns off completely at these times. Furthermore, simultaneous observations taken with the LOFAR, Westerbork, Lovell, and Effelsberg telescopes between 110 MHz and 2.7 GHz demonstrate that the transition between the Q mode and B mode occurs within one single rotation of the neutron star, and that it is concurrent across the range of frequencies observed.

  • 44.
    Stewart, A. J.
    et al.
    University of Oxford, UK ; University of Southampton, UK.
    Fender, R. P.
    University of Oxford, UK ; University of Southampton, UK.
    Broderick, J. W.
    University of Oxford, UK ; University of Southampton, UK ; ASTRON, The Netherlands.
    Hassall, T. E.
    University of Oxford, UK ; University of Southampton, UK.
    Muñoz-Darias, T.
    University of Oxford, UK ; University of Southampton, UK ; Instituto de Astrofísica de Canarias, Spain ; Universidad de La Laguna, Spain.
    Rowlinson, A.
    ASTRON, The Netherlands ; Anton Pannekoek Institute for Astronomy, The Netherlands.
    Swinbank, J. D.
    Anton Pannekoek Institute for Astronomy, The Netherlands ; Princeton University, USA.
    Staley, T. D.
    University of Oxford, UK ; University of Southampton, UK.
    Molenaar, G. J.
    Anton Pannekoek Institute for Astronomy, The Netherlands ; Rhodes University, South Africa.
    Scheers, B.
    Anton Pannekoek Institute for Astronomy, The Netherlands ; Centrum Wiskunde & Informatica, The Netherlands.
    Grobler, T. L.
    Pietka, M.
    Heald, G.
    McKean, J. P.
    Bell, M. E.
    Bonafede, A.
    Breton, R. P.
    Carbone, D.
    Cendes, Y.
    Clarke, A. O.
    Corbel, S.
    de Gasperin, F.
    Eislöffel, J.
    Falcke, H.
    Ferrari, C.
    Grießmeier, J. -M
    Hardcastle, M. J.
    Heesen, V.
    Hessels, J. W. T.
    Horneffer, A.
    Iacobelli, M.
    Jonker, P.
    Karastergiou, A.
    Kokotanekov, G.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Law, C. J.
    van Leeuwen, J.
    Markoff, S.
    Miller-Jones, J. C. A.
    Mulcahy, D.
    Orru, E.
    Pandey-Pommier, M.
    Pratley, L.
    Rol, E.
    Röttgering, H. J. A.
    Scaife, A. M. M.
    Shulevski, A.
    Sobey, C. A.
    Stappers, B. W.
    Tasse, C.
    van der Horst, A. J.
    van Velzen, S.
    van Weeren, R. J.
    Wijers, R. A. M. J.
    Wijnands, R.
    Wise, M.
    Zarka, P.
    Alexov, A.
    Anderson, J.
    Asgekar, A.
    Avruch, I. M.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Breitling, F.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    Conway, J. E.
    Corstanje, A.
    de Geus, E.
    Deller, A.
    Duscha, S.
    Frieswijk, W.
    Garrett, M. A.
    Gunst, A. W.
    van Haarlem, M. P.
    Hoeft, M.
    Hörandel, J.
    Juette, E.
    Kuper, G.
    Loose, M.
    Maat, P.
    McFadden, R.
    McKay-Bukowski, D.
    Moldon, J.
    Munk, H.
    Norden, M. J.
    Paas, H.
    Polatidis, A. G.
    Schwarz, D.
    Sluman, J.
    Smirnov, O.
    Steinmetz, M.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, M. C.
    Vermeulen, R.
    Vocks, C.
    Wijnholds, S. J.
    Wucknitz, O.
    Yatawatta, S.
    LOFAR MSSS: detection of a low-frequency radio transient in 400 h of monitoring of the North Celestial Pole2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 456, no 3, 2321-2342 p.Article in journal (Refereed)
    Abstract [en]

    We present the results of a four-month campaign searching for low-frequency radio transients near the North Celestial Pole with the Low-Frequency Array (LOFAR), as part of the Multifrequency Snapshot Sky Survey (MSSS). The data were recorded between 2011 December and 2012 April and comprised 2149 11-min snapshots, each covering 175 deg2. We have found one convincing candidate astrophysical transient, with a duration of a few minutes and a flux density at 60 MHz of 15–25 Jy. The transient does not repeat and has no obvious optical or high-energy counterpart, as a result of which its nature is unclear. The detection of this event implies a transient rate at 60 MHz of 3.9&#x2212;3.7+14.7&#x00D7;10&#x2212;4" style="position: relative;" tabindex="0" id="MathJax-Element-1-Frame" class="MathJax">3.9+14.7−3.7×10−4 d−1 deg−2, and a transient surface density of 1.5 × 10−5 deg−2, at a 7.9-Jy limiting flux density and ∼10-min time-scale. The campaign data were also searched for transients at a range of other time-scales, from 0.5 to 297 min, which allowed us to place a range of limits on transient rates at 60 MHz as a function of observation duration.

  • 45.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    A possible origin of gamma rays from the Fermi Bubbles2014In: Nuclear physics B, Proceedings supplements, ISSN 0920-5632, E-ISSN 1873-3832, Vol. 256-257, 125-130 p.Article in journal (Refereed)
    Abstract [en]

    One of the most exciting discoveries of recent years is a pair of gigantic gamma-ray emission regions, the so-called Fermi bubbles, above and below the Galactic center. The bubbles, discovered by the Fermi space telescope, extend up to ∼50°∼50° in Galactic latitude and are ∼40°∼40° wide in Galactic longitude. The gamma-ray emission is also found to correlate with radio, microwave and X-rays emission. The origin of the bubbles and the associated non-thermal emissions are still not clearly understood. Possible explanations for the non-thermal emission include cosmic-ray injection from the Galactic center by high speed Galactic winds/jets, acceleration by multiple shocks or plasma turbulence present inside the bubbles, and acceleration by strong shock waves associated with the expansion of the bubbles. In this paper, I will discuss the possibility that the gamma-ray emission is produced by the injection of Galactic cosmic-rays mainly protons during their diffusive propagation through the Galaxy. The protons interact with the bubble plasma producing π°π°-decay gamma rays, while at the same time, radio and microwave synchrotron emissions are produced by the secondary electrons/positrons resulting from the π±π± decays.

  • 46.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Cosmic ray proton spectrum below 100 TeV in the local region2006In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 370, no 1, 263-272 p.Article in journal (Refereed)
    Abstract [en]

    The propagation of cosmic ray (CR) protons in the Galaxy is discussed under the framework of a three-dimensional convection–diffusion model. Starting with the assumption of a uniform and continuous distribution of CR sources injecting CRs continuously in the Galaxy and by invoking a supernova explosion at various distances from the Earth, it is found that only those sources located within a distance of ∼1.5 kpc can produce appreciable temporal fluctuations in the CR proton flux observed near the Earth. So, the construction of the local CR proton spectrum is discussed by separating the contributions of the distant sources from that of the nearby sources. The contribution from the distant sources is treated in the framework of a continuous source distribution model in both space and time, but that of the nearby sources in a discrete space–time source model. The study predicts the presence of at least one old nearby source with a characteristic age of ∼105 yr located at a distance of ∼0.1 kpc to explain the observed proton flux below ∼100 GeV.

  • 47. Thoudam, Satyendra
    Diffuse gamma-ray emission of the galactic disk and Galactic Cosmic-Ray spectra2005In: International Cosmic Ray Conference, Pune, 2005, 2005, Vol. 4Conference paper (Refereed)
  • 48.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Effect of nearby supernova remnants on local cosmic rays2007In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 378, no 1, 48-54 p.Article in journal (Refereed)
    Abstract [en]

    We study in detail the effect of different particle release times from sources on the cosmic ray (CR) spectrum below 1015 eV in the Galaxy. We discuss different possible forms of particle injection such as burst-like injection, continuous injection for a finite time, injection from a stationary source and energy-dependent injection. When applied to the nearby known supernova remnants, we find that the observed CR anisotropy data favour the burst-like particle injection model for the CR diffusion coefficient D(E) ∝Ea with a= 0.3 –0.6 in the local region. In this study we have also found that the contribution of the sources G114.3+0.3 and Monogem dominate if the observed anisotropy is a result of the effect of the nearby sources. Further study shows that we should not neglect the contribution of the undetected old sources to the local CR anisotropy.

  • 49.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Fermi Bubble γ-Rays as a Result of Diffusive Injection of Galactic Cosmic Rays2013In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 778, no 1, 1-5 p., L20Article in journal (Refereed)
    Abstract [en]

    Recently, the Fermi Space Telescope discovered two large γ-ray emission regions, the so-called Fermi bubbles, that extend up to ~50° above and below the Galactic center (GC). The γ-ray emission from the bubbles is found to follow a hard spectrum with no significant spatial variation in intensity and spectral shape. The origin of the emission is still not clearly understood. Suggested explanations include the injection of cosmic-ray (CR) nuclei from the GC by high-speed Galactic winds, electron acceleration by multiple shocks, and stochastic electron acceleration inside the bubbles. In this Letter, it is proposed that the γ-rays may be the result of diffusive injection of Galactic CR protons during their propagation through the Galaxy. Considering that the bubbles are slowly expanding, and CRs undergo much slower diffusion inside the bubbles than in the average Galaxy and at the same time suffer losses due to adiabatic expansion and inelastic collisions with the bubble plasma, this model can explain the observed intensity profile, the emission spectrum and the measured luminosity without invoking any additional particle production processes, unlike other existing models.

  • 50.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Gamma rays from Fermi bubbles as due to diffusive injection of Galactic cosmic rays2014In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 742, 224-227 p.Article in journal (Refereed)
    Abstract [en]

    Recent detailed analysis of the Fermi-LAT data has discovered two giant γ-rayγ-ray emission regions, the so-called Fermi bubbles, extending up to ~50° in Galactic latitude above and below the Galactic center with a width of ~40° in longitude. The origin of the γ-rayγ-ray emission is not clearly understood. Here, we discuss the possibility that the γ-raysγ-rays can be the result of diffusive injection of Galactic cosmic-ray protons during their propagation through the Galaxy. In the model, we consider that the bubbles are slowly expanding, and cosmic rays undergo much slower diffusion inside the bubbles than in the averaged Galaxy. Moreover, we consider that cosmic rays inside the bubbles suffer losses from adiabatic expansion, and also from inelastic collisions with the bubble plasma producing pion-decay γ rays. We show that this simple model can explain some of the important properties of Fermi bubbles such as the measured γ-rayγ-ray intensity profile, the energy spectrum and the measured luminosity.

12 1 - 50 of 74
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