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  • 201.
    D’Ammando, F.
    et al.
    Universitá degli Studi di Bologna, Italy ; INAF – Istituto di Radioastronomia, Italy.
    Orienti, M.
    INAF – Istituto di Radioastronomia, Italy.
    Finke, J.
    U.S. Naval Research Laboratory, USA.
    Raiteri, C. M.
    INAF – Osservatorio Astrofisico di Torino, Italy.
    Hovatta, T.
    California Institute of Technology, USA.
    Larsson, J.
    Royal Institute of Technology, Sweden.
    Max-Moerbeck, W.
    National Radio Astronomy Observatory (NRAO), USA.
    Perkins, J.
    NASA Goddard Space Flight Center, USA.
    Readhead, A. C. S.
    California Institute of Technology, USA.
    Richards, J. L.
    Purdue University, USA.
    Beilicke, M.
    Washington University, USA.
    Benbow, W.
    Harvard-Smithsonian Center for Astrophysics, USA.
    Berger, K.
    University of Delaware, USA.
    Bird, R.
    University College Dublin, Ireland.
    Bugaev, V.
    Washington University, USA.
    Cardenzana, J. V.
    Iowa State University, USA.
    Cerruti, M.
    Harvard-Smithsonian Center for Astrophysics, USA.
    Chen, X.
    University of Potsdam, Germany ; DESY, Germany .
    Ciupik, L.
    Adler Planetarium and Astronomy Museum, USA.
    Dickinson, H. J.
    Iowa State University, USA.
    Eisch, J. D.
    Iowa State University, USA.
    Errando, M.
    Columbia University, USA.
    Falcone, A.
    Pennsylvania State University, USA .
    Finley, J. P.
    Purdue University, USA.
    Fleischhack, H.
    DESY, Germany.
    Fortin, P.
    Harvard-Smithsonian Center for Astrophysics, USA.
    Fortson, L.
    University of Minnesota, USA.
    Furniss, A.
    University of California, USA.
    Gerard, L.
    DESY, Germany.
    Gillanders, G. H.
    National University of Ireland Galway, Ireland.
    Griffiths, S. T.
    University of Iowa, USA.
    Grube, J.
    Adler Planetarium and Astronomy Museum, USA.
    Gyuk, G.
    Adler Planetarium and Astronomy Museum, USA.
    Håkansson, N.
    University of Potsdam, Germany.
    Holder, J.
    University of Delaware, USA.
    Humensky, T. B.
    Columbia University, USA.
    Kar, P.
    University of Utah, USA.
    Kertzman, M.
    DePauw University, USA.
    Khassen, Y.
    University College Dublin, Ireland.
    Kieda, D.
    University of Utah, USA.
    Krennrich, F.
    Iowa State University, USA.
    Kumar, S.
    University of Delaware, USA.
    Lang, M. J.
    National University of Ireland Galway, Ireland.
    Maier, G.
    DESY, Germany.
    McCann, A.
    University of Chicago, USA.
    Meagher, K.
    Georgia Institute of Technology, USA.
    Moriarty, P.
    National University of Ireland Galway, Ireland.
    Mukherjee, R.
    Columbia University, USA.
    Nieto, D.
    Columbia University, USA.
    de Bhróithe, A. O.
    DESY, Germany.
    Ong, R. A.
    University of California, USA.
    Otte, A. N.
    Georgia Institute of Technology, USA.
    Pohl, M.
    University of Potsdam, Germany ; DESY, Germany.
    Popkow, A.
    University of California, USA.
    Prokoph, Heike
    DESY, Germany.
    Pueschel, E.
    University College Dublin, Ireland.
    Quinn, J.
    University College Dublin, Ireland.
    Ragan, K.
    McGill University, Canada.
    Reynolds, P. T.
    Cork Institute of Technology, Ireland.
    Richards, G. T.
    Georgia Institute of Technology, USA.
    Roache, E.
    Harvard-Smithsonian Center for Astrophysics, USA.
    Rousselle, J.
    University of California, USA.
    Santander, M.
    Columbia University, USA.
    Sembroski, G. H.
    Purdue University, USA.
    Smith, A. W.
    University of Utah, USA.
    Staszak, D.
    McGill University, Canada.
    Telezhinsky, I.
    University of Potsdam, Germany ; DESY, Germany .
    Tucci, J. V.
    Purdue University, USA.
    Tyler, J.
    McGill University, Canada.
    Varlotta, A.
    Purdue University, USA.
    Vassiliev, V. V.
    University of California, USA.
    Wakely, S. P.
    University of Chicago, USA.
    Weinstein, A.
    Iowa State University, USA.
    Welsing, R.
    DESY, Germany.
    Williams, D. A.
    University of California, USA.
    Zitzer, B.
    Argonne National Laboratory, USA.
    The most powerful flaring activity from the NLSy1 PMN J0948+00222015Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 446, nr 3, s. 2456-2467Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on multifrequency observations performed during 2012 December–2013 August of the first narrow-line Seyfert 1 galaxy detected in γ-rays, PMN J0948+0022 (z = 0.5846). A γ-ray flare was observed by the Large Area Telescope on board Fermi during 2012 December–2013 January, reaching a daily peak flux in the 0.1–100 GeV energy range of (155 ± 31) × 10−8 ph cm−2 s−1 on 2013 January 1, corresponding to an apparent isotropic luminosity of ∼1.5 × 1048 erg s−1. The γ-ray flaring period triggered Swift and Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations in addition to radio and optical monitoring by Owens Valley Radio Observatory, Monitoring Of Jets in Active galactic nuclei with VLBA Experiments, and Catalina Real-time Transient Survey. A strong flare was observed in optical, UV, and X-rays on 2012 December 30, quasi-simultaneously to the γ-ray flare, reaching a record flux for this source from optical to γ-rays. VERITAS observations at very high energy (E > 100 GeV) during 2013 January 6–17 resulted in an upper limit of F>0.2 TeV < 4.0 × 10−12 ph cm−2 s−1. We compared the spectral energy distribution (SED) of the flaring state in 2013 January with that of an intermediate state observed in 2011. The two SEDs, modelled as synchrotron emission and an external Compton scattering of seed photons from a dust torus, can be modelled by changing both the electron distribution parameters and the magnetic field.

  • 202.
    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 telescope2005Ingår i: 29th International Cosmic Ray Conference Pune (2005), 2005, Vol. 4, s. 179-182Konferensbidrag (Refereegranskat)
    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.

  • 203.
    Dogiel, V. A.
    et al.
    National Central University, Taiwan ; P. N. Lebedev Physical Institute, Russia.
    Colafrancesco, S.
    INAF - Osservatorio Astronomico di Roma, Italy.
    Ko, C. M.
    National Central University, Taiwan.
    Kuo, P. H.
    National Central University, Taiwan.
    Hwang, C. Y.
    National Central University, Taiwan.
    Ip, W. H.
    National Central University, Taiwan.
    Birkinshaw, M.
    University of Bristol, UK.
    Prokhorov, Dmitry
    Moscow Institute of Physics and Technology, Russia.
    In-situ acceleration of subrelativistic electrons in the Coma halo and the halo’s influence on the Sunyaev-Zeldovich effect2007Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 461, nr 2, s. 433-443Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. The stochastic acceleration of subrelativistic electrons from a background plasma is studied in order to find a possible explanation of the hard X-ray emission detected from the Coma cluster. Methods. We calculate the necessary energy supply as a function of the plasma temperature and of the electron energy, and we show that, for the same value of the hard X-ray flux, the energy supply changes gradually from its high value for the case when emitting particle are non-thermal to lower values whenthe electrons are thermal. The kinetic equations we use include terms describing particle thermalization as well as momentum diffusion due to the Fermi IIacceleration. Results. We show that the temporal evolution of the particle distribution function has, at its final stationary stage, a rather specific form. This distribution function cannot be described by simple exponential or power-law expressions. A broad transfer region is formed by Coulomb collisions at energies betweenthe Maxwellian and power-law parts of the distribution functions. In this region the radiative lifetime of a single quasi-thermal electron differs greatly from thelifetime of the distribution function as a whole. For a plasma temperature of 8 keV, the particles emitting bremsstrahlung at 20-80 keV lie in this quasi-thermal regime. We show that the energy supply required by quasi-thermal electrons to produce the observed hard X-ray flux from Coma is one or two orders ofmagnitude smaller than the value derived from the assumption of a nonthermal origin of the emitting particles. This result may solve the problem of rapid cluster overheating by nonthermal electrons raised by Petrosian (2001): while Petrosian's estimates are correct for nonthermal particles, they are inapplicablein the quasi-thermal range. We finally analyze the change in Coma's Sunyaev-Zeldovich effect caused by the implied distortions of the Maxwellian spectrumof electrons, and we show that evidence for the acceleration of subrelativistic electrons can, in principle, be derived from detailed spectral measurements.

  • 204.
    Dogiel, Vladimir A.
    et al.
    Institute of Space and Astronautical Science, Japan ; P.N. Lebedev Institute, Russia.
    Chernyshov, Dmitry
    P.N. Lebedev Institute, Russia ; Moscow Institute of Physics and Technology, Russia.
    Yuasa, Takayuki
    The University of Tokyo, Japan.
    Prokhorov, Dmitry
    Moscow Institute of Physics and Technology, Russia ; Universit ́ e Pierre et Marie Curie, France.
    Cheng, Kwong-Sang
    University of Hong Kong, China.
    Bamba, Aya
    Institute of Space and Astronautical Science, Japan.
    Inoue, Hajime
    Institute of Space and Astronautical Science, Japan.
    Ko, Chung-Ming
    National Central University, Taiwan.
    Kokubun, Motohide
    Institute of Space and Astronautical Science, Japan.
    Maeda, Yoshitomo
    Institute of Space and Astronautical Science, Japan.
    Mitsuda, Kazuhisa
    Institute of Space and Astronautical Science, Japan.
    Nakazawa, Kazuhiro
    The University of Tokyo, Japan.
    Yamasaki, Noriko
    Institute of Space and Astronautical Science, Japan.
    Origin of Thermal and Non-Thermal Hard X-Ray Emissionfrom the Galactic Center2009Ingår i: Publications of the Astronomical Society of Japan, ISSN 0004-6264, Vol. 61, nr 5, s. 1099-1105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyse new results of Chandra and Suzaku Observatories which found a flux of hard X-ray emission from the compact region around Sgr A∗ (r ∼ 100 pc). We suppose that this emission is generated by accretion processes onto the central supermassive blackhole when an unbound part of captured stars obtains an additional momentum. As a result a flux of subrelativistic protons is generated near the galactic center which heats the background plasma up to temperatures about 6–10 keV and produces by inverse bremsstrahlung a flux of non-thermal X-ray emission in the energy range above 10 keV.

  • 205. 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 LOFAR2014Ingår i: AGU Fall Meeting Abstracts 2014, 2014Konferensbidrag (Refereegranskat)
  • 206.
    Eriksson, Urban
    et al.
    Uppsala University.
    Cedric, Linder
    Uppsala University.
    Airey, John
    Uppsala University.
    Redfors, Andreas
    Kristianstad University.
    Who needs 3D when the Universe is flat?2012Ingår i: The 1st World Conference on Physics Education, Istanbul, Turkey, 1-6 July, Istanbul, Turkey: WCPE , 2012, s. 170-171Konferensbidrag (Refereegranskat)
    Abstract [en]

    Learning astronomy can be difficult for students at all levels due to the highly diverse, conceptual and theoretical thinking used in the discipline. A variety of disciplinary-specific representations are normally employed to help students learn about the Universe. Some of the most common representations are twodimensional (2D) such as diagrams, plots, or images. In astronomy education there is an implicit assumption that students will be able to con- ceptually extrapolate three-dimensional (3D) representations from these 2D images (e.g., of nebulae); however, this is often not the case (Hansen et al. 2004a,b; Molina et al. 2004; Williamson and Abraham 1995; N.R.C. 2006, p. 56). The way in which students interact with different disciplinary represen- tations determines how much and what they will learn; yet, our literature review indicates that not much is known about this interaction. We have therefore chosen to investigate students’ reflective awareness evoked by 3D representations. Reflective awareness relates to the learning affordances that engagement with a collection of representations facilitates. The notion of reflection is drawn from the work of Schön (cf. 1983) in that it is related to our learning experience and involves the noticing of ‘new things’ and the noticing of ‘things’ in new ways as part of dealing with puzzling phenomena. Much of the research into Astronomy Education Research (AER) has been carried out at pre-university levels (Bailey and Slater 2003; Bailey 2011; Bre- tones and Neto 2011; Lelliott and Rollnick 2010), and furthermore very little has been grounded in a disciplinary discourse perspective (Airey and Linder 2009). Our study sets out to address both of these shortcomings. Our research question is: What is the nature of university students’ re- flective awareness when engaging with the representations used to illustrate the structural components and characteristics of the Milky Way Galaxy in a simulation video? Although not common, when 3D is introduced, then this is often done using video simulations. For our study we chose to use a highly regarded video simulation that illustrates some of the fundamental structural components of our Universe in a virtual reality journey through, and out of, our galaxy. In the study, the first 1.5-minutes of the video was set to automatically pause in seven places (these places where optimally determined in a small pre-study), and a web questionnaire was created to elicit the participants’ reflective awareness about the structural components and characteristics of the Milky Way in each clip. A total of 137 participants from physics and astronomy in Europe, North America, South Africa and Australia took part in the study. The written reflective descriptions from the survey were coded and sorted into constructed categories, using a constant comparison approach (cf. Gibbs 2002; Strauss 1998). Many of the participants expressed poor prior awareness of the 3D struc- ture of the universe, as evidenced by their ‘surprise’ in observing 3D features such as the large separation of the stars in Orion or the two nebulae in Orion. Many were also surprised by the extent of the grand scale of the (local) Uni- verse as they realised that the journey covers great distances in only a few seconds. In contrast, those participants who rated themselves as astronomy experts had already developed a 3D awareness of the universe. They used much more complex descriptions and to some extent commented on struc- tures and phenomena omitted from the simulation, such as HI-regions and infrared radiation from HII-regions, although these are invisible to the naked eye. In this talk we report on 3D-related issues, which we will discuss in re- lation to implications for using such a simulation as a resource intended to enhance the possibility of learning. There are two main findings of our study concerning 3D: firstly, one of the clearest differences in reflective awareness to emerge was that there was a gradual increase of awareness of structures and phenomena in relation to the educational level of the astronomy partic- ipants. Interestingly, this is not the case for the physics participants and we will argue that this is due to differences in the disciplinary discourses of physics and astronomy. The second finding is that the use of the simulation video successfully stimulated participants’ awareness of the 3D structure of the Universe as seen in their expressed surprise. We therefore argue that simula- tions can be a powerful and necessary tool in helping develop an awareness of the three-dimensional Universe and that simulations therefore are one of the critical forms of representation that open up the space for learning in astronomy.

  • 207.
    Eriksson, Urban
    et al.
    Uppsala University.
    Linder, Cedric
    Uppsala University.
    Airey, John
    Uppsala University.
    Redfors, Andreas
    Kristianstad University.
    Awareness of the three dimensional structure of the Universe2013Ingår i: The 21st Annual Conference of the Southern African Association for Research in Mathematics, Science and Technology Education, University of the Western Cape, Bellville, South Africa, 14 - 17 January, 2013, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Learning astronomy can be difficult for students at all levels due to the highly diverse, conceptual and theoretical thinking used in the discipline. A variety of disciplinary-specific representations are normally employed to help students learn about the Universe. Some of the most common representations are two-dimensional (2D) such as diagrams, plots, or images. In astronomy education there is an implicit assumption that students will be able to conceptually extrapolate three-dimensional (3D) representations from these 2D images (e.g., of nebulae); however, this is often not the case (Hansen, Barnett, MaKinster, & Keating, 2004a, 2004b; Molina, Redondo, Bravo, & Ortega, 2004; N.R.C, 2006; Williamson & Abraham, 1995).

    Simulation videos are often called on to dynamically introduce students to the structure and complexity of the Universe. We therefore chose to investigate, drawing on a range of educational experience, the nature of the reflective awareness evoked by being exposed to an array of 3D representations taken from a well-used simulation video in astronomy education. A key concept for this work is the notion of disciplinary affordances. Fredlund, Airey, and Linder (2012, p. 658) define the disciplinary affordances of a given representation as ―the inherent potential of that representation to provide access to disciplinary knowledge‖. Recent reviews indicate that most of the work done in astronomy education has taken place at a pre-university level and that none has focussed on disciplinary affordance vis-à-vis 3D representation (Bailey, 2011; Bailey & Slater, 2003; Bretones & Neto, 2011; Lelliott & Rollnick, 2010). The work reported here addresses both these shortcomings. 

    The simulation video used in our study was originally created by Brent Tully. After a pilot study a section of the video was selected to be cut into 7 clips (about 15s each). These clips formed the framing of a web survey that asked participants to write down their reflective awareness following after viewing of each video clip, for e.g. what comes to mind, things noticed, new realizations, etc. 

    A total of 137 participants from university physics and astronomy settings in Europe (42), North America (76), South Africa (3) and Australia (16) took part in the web survey (79 men and 58 women). The reflective descriptions from the survey were coded and used to construct categories, using a hermeneutic constant comparison approach (cf. Gibbs, 2002; Strauss & Corbin, 1998). 

    A limited number of categories emerged and were grouped under the overarching theme we decided to call Parallax. This was because Parallax captured all the statements reflecting awareness of the structural and positional affordances offered by the 3D-video. The analysis showed qualitative differences between the categories, where 3D refers to the highest level of awareness and Speed, travel or motion refers to the lowest level. There are also sub-categories, for e.g., for Speed, travel or motion there are two main ways of experiencing, either the observers or the observed objects, are described in terms of moving in a relative way. 

    Many of the novice participants expressed poor prior awareness of the 3D structure of the universe and surprise by the extent of the grand scale of the (local) Universe. In contrast, those participants who rated themselves as astronomy experts had already developed a 3D awareness of the universe. They used much more complex descriptions and to some extent commented on structures and phenomena omitted from the simulation, such as HI-regions and infrared radiation from HII-regions, although these are invisible to the naked eye. 

    The results show that these kinds of vividly visual and engaging simulations have the potential to provide new disciplinary knowledge for reflective learners in the field of astronomy. Such learning can be characterized as attaining a better appreciation of the disciplinary affordances of the representations used in the simulation. As a conclusion we will discuss how such engagement could open the way for astronomy students to learn more meaningfully about the structure and complexity of the Universe.

  • 208.
    Eriksson, Urban
    et al.
    Uppsala University.
    Linder, Cedric
    Uppsala University.
    Airey, John
    Uppsala University.
    Redfors, Andreas
    Kristianstad University.
    Tell me what you see: Differences in what is discerned when professors and students view the same disciplinary semiotic resource2014Ingår i: The 5th international 360° conference: Encompassing the Multimodality of Knowledge, May 8-10 2014, Aarhus, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Traditionally, astronomy and physics have been viewed as difficult subjects to master. The movement from everyday conceptions of the world around us to a disciplinary interpretation is fraught with pitfalls and problems. What characterises a disciplinary insider’s discernment of phenomena in astronomy and how does it compare to the views of newcomers to the field? In this paper we report on a study into what students and professors discern (cf. Eriksson et al, in press) from the same disciplinary semiotic resource and use this to propose an Anatomy of Disciplinary Discernment (ADD) as an overarching characterization of disciplinary learning.

    Students and professors in astronomy and physics were asked to describe what they could discern from a simulation video of travel through our Galaxy and beyond (Tully, 2012). In all, 137 people from nine countries participated. The descriptions were analysed using a hermeneutic, constant comparison approach (Seebohm, 2004; Strauss, 1987). Analysis culminated in the formulation of five hierarchically arranged, qualitatively different categories of discernment. This ADD modelling of the data consists of one non-disciplinary category and four levels of disciplinary discernment: Identification, Explanation, Appreciation, and Evaluation. Our analysis demonstrates a clear relationship between educational level and the level of disciplinary discernment.

    The analytic outcomes of the study suggest that teachers may create more effective learning environments by explicitly crafting their teaching to support the discernment of various aspects of disciplinary semiotic resources in order to facilitate the crossing of boundaries in the ADD model.

  • 209.
    Eriksson, Urban
    et al.
    Uppsala University.
    Linder, Cedric
    Uppsala University.
    Airey, John
    Uppsala University.
    Redfors, Andreas
    Kristianstad University.
    The Anatomy of Disciplinary Discernment: An argument for a spiral trajectory of learning in physics education2014Ingår i: The First Conference of the International Association for Cognitive Semiotics (IACS), Lund, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Traditionally, physics has been viewed as a difficult subject to master. The movement from everyday conceptions of the world around us to a disciplinary interpretation is fraught with problems. What characterises this disciplinary development from learner to expert? In this presentation we report on a study involving what students and professors discern from a disciplinary representation and use this to propose an Anatomy of Disciplinary Discernment (ADD) as an overarching characterization of disciplinary learning. To do this we bring together three important educational ideas – first, Bruner’s (1960) notion of the spiral curriculum. Second, Fredlund, Airey, and Linder’s (2012) notion of disciplinary affordances -- the ‘inherent potential of a representation to provide access to disciplinary knowledge’. Thirdly Eriksson, Linder, Airey, and Redfors’ (2013) notion of disciplinary discernment -- noticing something (eg. Mason, 2002), reflecting on it (Schön, 1983), and constructing (disciplinary) meaning (Marton & Booth, 1997).

    Students in astronomy and their teaching professors were asked to describe what they discerned from a simulation video of travel through our galaxy and beyond. In all, 137 people from nine countries participated. The descriptions were analysed using a standard interpretive study approach (Erickson, 1986; Gallagher, 1991). This resulted in the formulation of five qualitatively different categories of discernment.

    We found that these categories of disciplinary discernment could be arranged into an anatomy of hierarchically increasing levels of disciplinary discernment and subsequently the idea of ADD with a unit of analysis being the discernment of disciplinary affordance. The ADD modelling for the data incorporated four increasing levels disciplinary discernment: Identification, Explanation, Appreciation, and Evaluation. The visualization of the analysis demonstrates a clear relationship between educational level and the level of disciplinary discernment. Hence, the ADD can be seen to be related to Bruner’s concept of the spiral curriculum idea and through this relationship projects a learning trajectory that students experience while moving through the educational system.

    The analytic outcomes of the study suggest how teachers may gain insight into how to create more effective learning environments for students to successfully negotiate a required learning trajectory by explicitly crafting the teaching to support the crossing of boundaries.

  • 210.
    Eriksson, Urban
    et al.
    Uppsala University.
    Linder, Cedric
    Uppsala University.
    Airey, John
    Linnéuniversitetet, Fakultetsnämnden för humaniora och samhällsvetenskap, Institutionen för språk och litteratur, SOL. Uppsala University.
    Redfors, Andreas
    Kristianstad University.
    Who needs 3D when the Universe is flat?2012Ingår i: Gordon Research Conference Astronomy's Discoveries and Physics Education, June 17-22, 2012, Waterville: Colby Collage , 2012Konferensbidrag (Refereegranskat)
  • 211.
    Franke, R.
    et al.
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    Holler, M.
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    Kaminsky, B.
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    Karg, T.
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    Prokoph, Heike
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    Schönwald, A.
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    Schwerdt, C.
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    Stößl, A.
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    Walter, M.
    Deutsches Elektronen-Synchrotron (DESY), Germany.
    CosMO - a cosmic muon observer experiment for students2013Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    What are cosmic particles and where do they come from? These are questions which are not only fascinating for scientists. With the CosMO experiment high-school students can perform their own hands-on experiments and become familiar with modern scientific working methods. The detector consists of three scintillation counter boxes. An electronic board, developed by Fermilab for the QuarkNet Project, realizes the trigger condition, the data acquisition and the GPS data taking. With a Python program running on a netbook under Linux, the trigger and data taking conditions can be defined. The program also manages the data storage and the online display of particle rates. All components fit into a single notebook bag. The detector can also be operated with a small 5 Volt battery pack, independently from the power grid. Possible student experiments comprise, for instance, the measurement of cosmic particle rates in dependence on the zenith angle, particle showers in dependence on the detector distance, and the lifetime of muons. Twenty detectors have been built by DESY. They are used within the German outreach network "Netzwerk Teilchenwelt" by 15 astroparticle-research institutes for practical project works. The network program also includes workshops for teachers and the mentoring of the experiments performed by school students.

  • 212.
    Fransson, Emma
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE). Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för datavetenskap (DV).
    High energy gamma ray emission and multi-wavelength view of the AGN PKS 0537-4412017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This thesis describes the analysis of Very High Energy (VHE) emission from the Active Galactic Nucleus PKS 0537-441. It also aims to put the results in a wider context by implementing previous work done on this source. The data chosen for the analysis is provided by the Fermi-LAT satellite and covers the energy range between 300 MeV and 300 GeV. Initially a lightcurve of the received flux from the source was generated, containing data from August 2008 to April 2017, with a mean flux of 4∗10−8 photons per second per squared centimeter. The lightcurve contained sections of different flux intensities giving periods of special interest, such as a flaring period at August 2008 to August 2011, an enormous flare at April 2010 and a less active period between April 2013 - January 2016 that could be identified for further investigations. The differences in observed flux over time was tested and PKS 0537-441 was found to be a significantly variable source. Spectral Energy Distribution (SED) analysis was performed over both the entire period as well as over the selected subperiods and fitted against models using the tools provided by the Fermi Science Support Center (FSSC). The models used in the fitting was PowerLaw2, LogParabola and PLSuperExpCutoff and the best fit for the data was obtained from the PLSuperExpCutoff, except for the less intense period where the LogParabola gave the best fit. The result from the SED analysis was integrated with results from previous work done on the source, ranging over multiple wavelengths in order to get a SED which spanned over the entire electromagnetic spectrum. Finally, modeling of this multi wavelength SED was performed in order to obtain parameters for the physical processes involved in the creation of the radiation received from PKS 0537-441.

  • 213.
    Füßling, Matthias
    et al.
    Deutsches Elektronen-Synchrotron, Germany.
    Oya, Igor
    Deutsches Elektronen-Synchrotron, Germany.
    Balzer, Arnim
    University of Amsterdam, The Netherlands.
    Berge, David
    University of Amsterdam, The Netherlands.
    Borkowski, Jerzy
    Nicolaus Copernicus Astronomical Center, Poland.
    Conforti, Vito
    INAF - IASF Bologna, Italy.
    Colomé, Josep
    University of Barcelona, Spain.
    Lindemann, Rico
    Deutsches Elektronen-Synchrotron, Germany.
    Lyard, Etienne
    University of Geneva, Switzerland.
    Melkumyan, David
    Deutsches Elektronen-Synchrotron, Germany.
    Punch, Michael
    Paris Diderot University.
    Schwanke, Ullrich
    Humboldt University of Berlin, Germany.
    Schwarz, Joseph
    Brera Astronomical Observatory, Italy.
    Tanci, Claudio
    University of Perugia, Italy.
    Tosti, Gino
    University of Perugia, Italy.
    Wegner, Peter
    Deutsches Elektronen-Synchrotron, Germany.
    Wischnewski, Ralf
    Deutsches Elektronen-Synchrotron, Germany.
    Weinstein, Amanda
    Iowa State University, USA.
    Status of the array control and data acquisition system for the Cherenkov Telescope Array2016Ingår i: Software and Cyberinfrastructure for Astronomy IV / [ed] Gianluca Chiozzi, Juan C. Guzman, SPIE - International Society for Optical Engineering, 2016, artikel-id 99133CKonferensbidrag (Refereegranskat)
    Abstract [en]

    The Cherenkov Telescope Array (CTA) will be the next-generation ground-based observatory using the atmospheric Cherenkov technique. The CTA instrument will allow researchers to explore the gamma-ray sky in the energy range from 20 GeV to 300 TeV. CTA will comprise two arrays of telescopes, one with about 100 telescopes in the Southern hemisphere and another smaller array of telescopes in the North. CTA poses novel challenges in the field of ground-based Cherenkov astronomy, due to the demands of operating an observatory composed of a large and distributed system with the needed robustness and reliability that characterize an observatory. The array control and data acquisition system of CTA (ACTL) provides the means to control, readout and monitor the telescopes and equipment of the CTA arrays. The ACTL system must be flexible and reliable enough to permit the simultaneous and automatic control of multiple sub-arrays of telescopes with a minimum effort of the personnel on-site. In addition, the system must be able to react to external factors such as changing weather conditions and loss of telescopes and, on short timescales, to incoming scientific alerts from time-critical transient phenomena. The ACTL system provides the means to time-stamp, readout, filter and store the scientific data at aggregated rates of a few GB/s. Monitoring information from tens of thousands of hardware elements need to be channeled to high performance database systems and will be used to identify potential problems in the instrumentation. This contribution provides an overview of the ACTL system and a status report of the ACTL project within CTA.

  • 214.
    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 reconstruction2015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 575, nr A90Artikel i tidskrift (Refereegranskat)
    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.

  • 215.
    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 LOFAR2016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, artikel-id A3Artikel i tidskrift (Refereegranskat)
    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.

  • 216. Glicenstein, J-F
    et al.
    Barcelo, M.
    Barrio, J-A
    Blanch, O.
    Boix, J.
    Bolmont, J.
    Boutonnet, C.
    Brun, P.
    Chabanne, E.
    Champion, C.
    Colonges, S.
    Corona, P.
    Courty, B.
    Delagnes, E.
    Delgado, C.
    Diaz, C.
    Ernenwein, J-P
    Fegan, S.
    Ferreira, O.
    Fesquet, M.
    Fontaine, G.
    Fouque, N.
    Henault, F.
    Gascon, D.
    Giebels, B.
    Herranz, D.
    Hermel, R.
    Hoffmann, D.
    Horan, D.
    Houles, J.
    Jean, P.
    Karkar, S.
    Knoedlseder, J.
    Martinez, G.
    Lamanna, G.
    LeFlour, T.
    Leveque, A.
    Lopez-Coto, R.
    Louis, F.
    Moudden, Y.
    Moulin, E.
    Nayman, P.
    Nunio, F.
    Olives, J-F
    Panazol, J-L
    Pavy, S.
    Petrucci, P-O
    Punch, Michael
    Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
    Prast, J.
    Ramons, P.
    Rateau, S.
    Rib'o, M.
    Rosier-Lees, S.
    Sanuy, A.
    Sizun, P.
    Sieiro, J.
    Sulanke, K-H
    Tavernet, J-P
    Tejedor, L. A.
    Toussenel, F.
    Vasileiadis, G.
    Voisin, V.
    Waegeberts, V.
    Zurbach, C.
    Status of the NectarCAM camera project2014Ingår i: High Energy, Optical, and Infrared Detectors for Astronomy VI, SPIE - International Society for Optical Engineering, 2014, artikel-id 91541DKonferensbidrag (Refereegranskat)
    Abstract [en]

    NectarCAM is a camera designed for the medium-sized telescopes of the Cherenkov Telescope Array (CTA) covering the central energy range 100 GeV to 30 TeV. It has a modular design based on the NECTAr chip, at the heart of which is a GHz sampling Switched Capacitor Array and 12-bit Analog to Digital converter. The camera will be equipped with 265 7-photomultiplier modules, covering a field of view of 7 to 8 degrees. Each module includes the photomultiplier bases, High Voltage supply, pre-amplifier, trigger, readout and Thernet transceiver. Events recorded last between a few nanoseconds and tens of nanoseconds. A flexible trigger scheme allows to read out very long events. NectarCAM can sustain a data rate of 10 kHz. The camera concept, the design and tests of the various subcomponents and results of thermal and electrical prototypes are presented. The design includes the mechanical structure, the cooling of electronics, read-out, clock distribution, slow control, data-acquisition, trigger, monitoring and services. A 133-pixel prototype with full scale mechanics, cooling, data acquisition and slow control will be built at the end of 2014.

  • 217.
    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 052007Ingår i: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 34, s. 1683-1695Artikel i tidskrift (Refereegranskat)
    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.

  • 218.
    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 062008Ingår i: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 35, nr 6, artikel-id 065202Artikel i tidskrift (Refereegranskat)
    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.

  • 219.
    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 Telescopes2005Ingår i: 29th International Cosmic Ray Conference Pune (2005), 2005, Vol. 4Konferensbidrag (Refereegranskat)
    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.

  • 220.
    Gächter Sundbäck, Dominic
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Analysis of the Hard Spectrum BL Lac Source 1H 1914-194 with Fermi-LAT Data and Multiwavelength Modelling2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The very-high-energy gamma-ray emission of the hard spectrum BL Lac source 1H1914-194 has been studied with Fermi-LAT data covering a nearly ten-year period between August 2008 until March 2018 in the energy range of 300 MeV to 870 GeV. The mean flux has been determined as 8.4 x 10-9±3.5 x 10-10 photon cm-2 s-1. The data processing has been done with the Enrico software using the Fermi Science Tools (v10r0p5) and the Pass 8 version of the data, performing binned analysis in order to handle the long integration time. The lightcurve shows that the source has to be considered as variable in the given time period for a three-month binning. It gives furthermore evidence for at least one quiet and active period lasting slightly over 1.5 years each. Even these shorter periods show a weak variability. The significance of the source has been determined as σ = 57.5 for a one-year period. The spectral analysis of three different time periods have been fitted by PowerLaw2, LogParabola and PLExpCutoff functions resulting in LogParabola being slightly favored in most of the cases. However, the test statistic are not showing enough significance that may lead to an unambiguous preference. The data from the analysis has been implemented in a multiwavelength view of the source, showing that the analysis is in agreement with the data coming from the Fermi catalogs. The overall emission of 1H1914-194 has been modelled with theoretical frameworks based on a one-zone Synchrotron Self Compton (SSC) model providing an acceptable description of the SED.

  • 221. 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 results2015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 582, s. 1-22, artikel-id A123Artikel i tidskrift (Refereegranskat)
    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.

  • 222.
    Henault, Franois
    et al.
    Joseph Fourier University, France.
    Petrucci, Pierre-Olivier
    Joseph Fourier University, France.
    Jocou, Laurent
    Joseph Fourier University, France.
    Khelifi, Bruno
    Ecole Polytechnique, France.
    Manigot, Pascal
    Ecole Polytechnique, France.
    Hormigos, Stephane
    Ecole Polytechnique, France.
    Knoedlseder, Juergen
    Institut de recherche en astrophysique et planétologie, France.
    Olive, Jean-Francois
    Institut de recherche en astrophysique et planétologie, France.
    Jean, Pierre
    Institut de recherche en astrophysique et planétologie, France.
    Punch, Michael
    Paris Diderot University, France.
    Design of light concentrators for Cherenkov telescope observatories2013Ingår i: Nonimaging Optics: Efficient Design for Illumination and Solar Concentration X / [ed] Roland Winston, Jeffrey Gordon, 2013, artikel-id 883405Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Cherenkov Telescope Array (CTA) will be the largest cosmic gamma ray detector ever built in the world. It will be installed at two different sites in the North and South hemispheres and should be operational for about 30 years. In order to cover the desired energy range, the CTA is composed of typically 50-100 collecting telescopes of various sizes (from 6 to 24-m diameters). Most of them are equipped with a focal plane camera consisting of 1500 to 2000 Photomultipliers (PM) equipped with light concentrating optics, whose double function is to maximize the amount of Cherenkov light detected by the photo-sensors, and to block any stray light originating from the terrestrial environment. Two different optical solutions have been designed, respectively based on a Compound Parabolic Concentrator (CPC), and on a purely dioptric concentrating lens. In this communication are described the technical specifications, optical designs and performance of the different solutions envisioned for all these light concentrators. The current status of their prototyping activities is also given.

  • 223.
    Holler, M.
    et al.
    École Polytechnique, France.
    Berge, D.
    University of Amsterdam, Netherlands.
    van Eldik, C.
    Erlangen Centre for Astroparticle Physics, Germany.
    Lenain, J.-P.
    LPNHE Paris, France.
    Marandon, V.
    Max-Planck-Institut für Kernphysik, Germany.
    Murach, T.
    Humboldt-Universität zu Berlin, Germany.
    de Naurois, M.
    École Polytechnique, France.
    Parsons, R. D.
    Max-Planck-Institut für Kernphysik,. Germany.
    Prokoph, Heike
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Zaborov, D.
    École Polytechnique, France.
    Collaboration, for the H. E. S. S.
    Observations of the Crab Nebula with H.E.S.S. Phase II2015Ingår i: Proceedings of Science, 2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The High Energy Stereoscopic System (H.E.S.S.) phase I instrument was an array of four 100m2 mirror area Imaging Atmospheric Cherenkov Telescopes (IACTs) that has very successfully mapped the sky at photon energies above ∼ 100GeV. Recently, a 600m2 telescope was added to the centre of the existing array, which can be operated either in standalone mode or jointly with the four smaller telescopes. The large telescope lowers the energy threshold for gamma-ray observations to several tens of GeV, making the array sensitive at energies where the Fermi-LAT instrument runs out of statistics. At the same time, the new telescope makes the H.E.S.S. phase II instrument. This is the first hybrid IACT array, as it operates telescopes of different size (and hence different trigger rates) and different field of view. In this contribution we present results of H.E.S.S. phase II observations of the Crab Nebula, compare them to earlier observations, and evaluate the performance of the new instrument with Monte Carlo simulations.

  • 224.
    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
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE). 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 LOFAR2017Ingår i: RICAP16, 6TH ROMA INTERNATIONAL CONFERENCE ON ASTROPARTICLE PHYSICS / [ed] Morselli, A Capone, A Fernandez, GR, 2017, artikel-id UNSP 02001Konferensbidrag (Refereegranskat)
    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.

  • 225.
    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 LOFAR2010Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 617, nr 1-3, s. 482-483Artikel i tidskrift (Refereegranskat)
    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.

  • 226. IceCube Collaboration, Group Authors
    et al.
    Fermi-LAT Collaboration, Group Authors
    MAGIC Collaboration, Group Authors
    AGILE, Group Authors
    ASAS-SN, Group Authors
    HAWC, Group Authors
    HESS, Group Authors
    INTEGRAL, Group Authors
    Kanata, Group Authors
    Kiso Subaru Observing Te, Group Authors
    Kapteyn, Group Authors
    Liverpool Telescope, Group Authors
    Swift NuSTAR, Group Authors
    VERITAS, Group Authors
    VLA 17B-403 Team, Group Authors
    Becherini, Yvonne
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A2018Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 361, nr 146, s. 1-8, artikel-id eaat1378Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera–electronvolts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray–emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

  • 227. 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 field2014Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, s. 1-12, artikel-id A101Artikel i tidskrift (Refereegranskat)
    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%.

  • 228. Karlsson, Thomas
    et al.
    Hans, Bengtsson
    Wikander, Tomas
    Holmberg, Gustav
    Wahlström, Robert
    Allen, Christopher
    50 Forgotten Miras2016Ingår i: Journal of the American Association of Variable Star Observers, ISSN 0271-9053, Vol. 44, nr 2, s. 156-163Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the results of 4 years observing of 50 poorly studied Mira stars. 247 maxima and 241 minima together with current period elements, ranges, and color indices for the stars are presented. “50 forgotten Miras” is an ongoing observing program run by the Variable star section of the Association of Swedish Amateur Astronomers (SAAF/V) that started in 2012.

  • 229.
    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 telescope2007Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 578, nr 3, s. 548-564Artikel i tidskrift (Refereegranskat)
    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.

  • 230.
    Linder, Cedric
    et al.
    Uppsala University.
    Eriksson, Urban
    Uppsala University ; Kristianstad University.
    Airey, John
    Uppsala University.
    Redfors, Andreas
    Kristianstad University.
    The overlooked challenge of learning to extrapolate three-dimensionality2013Ingår i: Book of Abstracts: ICPE-EPEC 2013, The International Conference on Physics Education, August 5-9, 2013 Prague, Czech Republic, Charles University , 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Learning astronomy has many learning challenges due to the highly diverse, conceptual, and theoretical thinking used in the discipline. One taken for granted challenge is the learning to extrapolate three-dimensionality. Although we have the ability to see our surroundings in threedimensional terms, beyond a distance of about 200m this ability quickly becomes very limited. So, when looking up at the night sky, learning to discern critical features that are embedded in dimensionality does not come easily. There have been several articles addressing how fruitful 3D simulations are for astronomy education, but they do not address what students discern, nor the nature of that discernment. Taking the concept of discernment to be about noticing something and assigning meaning to it, our research question is: In terms of dimensionality, what do astronomy/physics students and professors discern when engaging with a simulated video flythrough of our Galaxy and beyond?

    A web-based questionnaire was designed using links to video clips drawn from a well-regarded simulation-video of travel through our galaxy and beyond. 137 physics and astronomy university students and teaching professors, who were drawn from nine countries, completed the questionnaire. The descriptions provided by them were used to formulate six categories of discernment in relation to multidimensionality. These results are used to make the case that astronomy learning that aims at developing the ability to extrapolate three-dimensionality needs to be grounded in the creation of meaningful motion parallax experiences. Teaching and learning implications are discussed.

  • 231.
    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 survey2015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 574, artikel-id A73Artikel i tidskrift (Refereegranskat)
    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.

  • 232. 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 bursts2014Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, s. 1-8, artikel-id A67Artikel i tidskrift (Refereegranskat)
    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.

  • 233.
    Mulrey, K.
    et al.
    Vrije Univ Brussel, Belgium.
    Bonardi, A.
    Radboud Univ Nijmegen, Netherlands.
    Buitink, S.
    Vrije Univ Brussel, Belgium;Radboud Univ Nijmegen, Netherlands.
    Corstanje, A.
    Radboud Univ Nijmegen, Netherlands.
    Falcke, H.
    Radboud Univ Nijmegen, Netherlands;Nikhef, Netherlands;Netherlands Inst Radio Astron ASTRON, Netherlands.
    Hare, B. M.
    Univ Groningen, Netherlands.
    Horandel, J. R.
    Radboud Univ Nijmegen, Netherlands;Nikhef, Netherlands;Vrije Univ Brussel, Belgium.
    Huege, T.
    Vrije Univ Brussel, Belgium;KIT, Germany.
    Mitra, P.
    Vrije Univ Brussel, Belgium.
    Nelles, A.
    DESY, Germany;Humboldt Univ, Germany.
    Rachen, J. P.
    Radboud Univ Nijmegen, Netherlands.
    Rossetto, L.
    Radboud Univ Nijmegen, Netherlands.
    Schellart, P.
    Radboud Univ Nijmegen, Netherlands;Princeton Univ, USA.
    Scholtene, O.
    Univ Groningen, Netherlands;Vrije Univ Brussel, Belgium.
    ter Veen, S.
    Radboud Univ Nijmegen, Netherlands;Netherlands Inst Radio Astron ASTRON, Netherlands.
    Thoudam, Satyendra
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE). Radboud Univ Nijmegen, Netherlands.
    Trinh, T. N. G.
    Univ Groningen, Netherlands.
    Winchen, T.
    Vrije Univ Brussel, Belgium.
    Calibration of the LOFAR low-band antennas using the Galaxy and a model of the signal chain2019Ingår i: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 111, s. 1-11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The LOw-Frequency ARray (LOFAR) is used to make precise measurements of radio emission from extensive air showers, yielding information about the primary cosmic ray. Interpreting the measured data requires an absolute and frequency-dependent calibration of the LOFAR system response. This is particularly important for spectral analyses, because the shape of the detected signal holds information about the shower development. We revisit the calibration of the LOFAR antennas in the range of 30-80 MHz. Using the Galactic emission and a detailed model of the LOFAR signal chain, we find an improved calibration that provides an absolute energy scale and allows for the study of frequency dependent features in measured signals. With the new calibration, systematic uncertainties of 13% are reached, and comparisons of the spectral shape of calibrated data with simulations show promising agreement. (C) 2019 Elsevier B.V. All rights reserved.

  • 234.
    Mulrey, K.
    et al.
    Vrije Universiteit Brussel, Belgium.
    Bonardi, A.
    Radboud University, Netherlands.
    Buitink, S.
    Vrije Universiteit Brussel, Belgium.
    Corstanje, A.
    Radboud University, Netherlands.
    Falcke, H.
    Radboud University, Netherlands;NIKHEF Science Park Amsterdam, Netherlands;Netherlands Institute of Radio Astronomy (ASTRON), Netherlands.
    Hare, B. M.
    University Groningen, Netherlands.
    Hörandel, J. R.
    Radboud University, Netherlands;NIKHEF Science Park Amsterdam, Netherlands.
    Mitra, P.
    Vrije Universiteit Brussel, Belgium.
    Nelles, A.
    Radboud University, Netherlands;University of California Irvine, USA.
    Rachen, J. P.
    Radboud University, Netherlands.
    Rossetto, L.
    Radboud University, Netherlands.
    Schellart, P.
    Radboud University, Netherlands;Princeton University, USA.
    Scholten, O.
    University Groningen, Netherlands;Vrije Universiteit Brussel, Belgium.
    Ter Veen, S.
    Radboud University, Netherlands;Netherlands Institute of Radio Astronomy (ASTRON), Netherlands.
    Thoudam, Satyendra
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE). Radboud University, Netherlands.
    Trinh, T. N. G.
    University Groningen, Netherlands.
    Winchen, T.
    Vrije Universiteit Brussel, Belgium.
    Expansion of the LOFAR radboud air shower array2018Ingår i: Proceedings of Science: 35th International Cosmic Ray Conference — ICRC2017. 10–20 July, 2017. Bexco, Busan, Korea, Sissa Medialab Srl , 2018, artikel-id 413Konferensbidrag (Refereegranskat)
    Abstract [en]

    The LOFAR Radboud Air Shower Array (LORA) consists of 20 plastic scintillators and is situated at the core of the LOFAR radio telescope. LORA detects particles from extensive air showers and triggers the read-out of the LOFAR antennas. The dense LOFAR antenna spacing allows for detailed sampling of the radio emission generated in extensive air showers, which yields high precision reconstruction of cosmic ray properties and information about the shower development. We discuss the proposed expansion of LORA, including the addition of scintillator units and the implementation of triggering algorithms that will probe more details of the radio emission and detect lower energy showers without introducing a composition bias, which is important for studying the origin of cosmic rays.

  • 235.
    Möllerström, Tobias
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Analysis of the high-energy emission of the BL Lac PKS 2155-304 with Fermi-LAT data2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Some of the most interesting objects in the Universe are Active Galactic Nuclei. In the centre of an active galaxy is a supermassive black hole that accretes matter from the surrounding galaxy. In the process, not yet fully understood, some of the matter is ejected in two jets, perpendicular to the plane of the galaxy. The energy of the particles in the jets are extremely high, sometimes over 1019 eV. The features of an active galaxy can be very different depending on from which angle it is viewed. This means that some astronomical objects that earlier seemed to be very heterogeneous might be only different manifestations of the same type of object, namely active galactic nuclei. This thesis introduces some of these different objects. The unifying theory is described. Ways of detecting the high-energy radiation and two important instruments, H.E.S.S. and Fermi-LAT are described. Three studies of the BL Lac PKS 2155-304, an active galactic nucleus that points its jet almost straight at Earth, are made using Fermi-LAT data. The conclusion of the studies is that the source is variable at least in the time scale of days and that in order to gather further information about these objects simultaneous multi-wavelength surveys have to be done. 

  • 236. 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 maximum2015Ingår i: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 5Artikel i tidskrift (Refereegranskat)
    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.

  • 237. 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 LOFAR2015Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 632, nr 1, s. 1-11Artikel i tidskrift (Refereegranskat)
    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.

  • 238. 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 LOFAR2015Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 10Artikel i tidskrift (Refereegranskat)
    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.

  • 239. 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 LOFAR2015Ingår i: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 65, s. 11-21Artikel i tidskrift (Refereegranskat)
    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.

  • 240.
    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 LOFAR2013Ingår i: 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, s. 105-110Konferensbidrag (Refereegranskat)
    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.

  • 241. 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 A2014Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 437, nr 4, s. 3506-3515Artikel i tidskrift (Refereegranskat)
    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.

  • 242. 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 doubeltjes2015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 584, s. 1-12, artikel-id A112Artikel i tidskrift (Refereegranskat)
    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.

  • 243.
    Panchal, N.
    et al.
    Homi Bhabha Natl Inst, India;Tata Inst Fundamental Res, India.
    Senniappan, Mohanraj
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE). Homi Bhabha Natl Inst, India;Tata Inst Fundamental Res, India.
    Kumar, A.
    Homi Bhabha Natl Inst, India;Tata Inst Fundamental Res, India.
    Dey, T.
    Homi Bhabha Natl Inst, India;Tata Inst Fundamental Res, India.
    Majumder, G.
    Tata Inst Fundamental Res, India.
    Shinde, R.
    Tata Inst Fundamental Res, India.
    Verma, P.
    Tata Inst Fundamental Res, India.
    Satyanarayana, B.
    Tata Inst Fundamental Res, India.
    Datar, V. M.
    Tata Inst Fundamental Res, India.
    A compact cosmic muon veto detector and possible use with the Iron Calorimeter detector for neutrinos2017Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 12, artikel-id T11002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The motivation for a cosmic muon veto (CMV) detector is to explore the possibility of locating the proposed large Iron Calorimeter (ICAL) detector at the India based Neutrino Observatory (INO) at a shallow depth. An initial effort in that direction, through the assembly and testing of a similar to 1 m x 1 m x 0.3 m plastic scintillator based detector, is described. The plan for making a CMV detector for a smaller prototype mini-ICAL is also outlined.

  • 244.
    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 LOFAR2016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 586, artikel-id A92Artikel i tidskrift (Refereegranskat)
    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.

  • 245. Pita, S.
    et al.
    Goldoni, P.
    Boisson, C.
    Becherini, Yvonne
    Gerard, L.
    Lenain, J. -P
    Punch, Michael
    High energy blazars spectroscopy with X-Shooter on the VLT2012Ingår i: High energy gamma-ray astronomy, American Institute of Physics (AIP), 2012, s. 566-569Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present results of observations in the UV to near-IR range for eight blazars, three of which have been recently discovered at Very High Energies (VHE) and five appearing as interesting candidates for VHE gamma-ray detection. We focus in this paper on the search for their redshifts, which are unknown or considered as uncertain.

  • 246. Pita, S.
    et al.
    Goldoni, P.
    Boisson, C.
    Lenain, J. -P
    Punch, Michael
    Paris Diderot University, France.
    Gerard, L.
    Hammer, F.
    Kaper, L.
    Sol, H.
    Spectroscopy of high-energy BL Lacertae objects with X-shooter on the VLT2014Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 565, s. 1-20, artikel-id A12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. BL Lac objects detected in gamma-rays and, particularly, those detected at very high energies (E > 100 GeV) by Cherenkov telescopes are extreme sources with most having redshifts lower than 0.2. Their study gives insights on the acceleration mechanisms in play in such systems and is also a valuable tool for putting constraints on the density of extragalactic background light, especially if several objects are detected at different redshifts. As their spectra are dominated by the non-thermal emission of the jet and the spectral features are weak and narrow in the optical domain, measuring their redshift is challenging. However, such a measure is fundamental as it allows a firm determination of the distance and luminosity of the source, and, therefore, a consistent model of its emission. Aims. Measurement of the redshift of BL Lac objects detected in gamma-rays and determination of global properties of their host galaxies is the aim of this study. Methods. We observed a sample of eight BL Lac objects with the X-shooter spectrograph installed at the ESO Very Large Telescope (VLT) to take advantage of its unprecedented wavelength coverage and its resolution, which is about five times higher than generally used in such studies. We extracted UVB to NIR spectra that we then corrected for telluric absorption and calibrated in flux. We systematically searched for spectral features. When possible, we determined the contribution of the host galaxy to the overall emission. Results. Of the eight BL Lac sources, we measured the redshift of five of them and determined lower limits for two through the detection of intervening systems. All seven of these objects have redshifts greater than 0.2. For the remaining one, we estimated, using an indirect method, that its redshift is greater than 0.175. In two cases, we refuted redshift values reported in other publications. Through careful modelling, we determined the magnitude of the host galaxies. In two cases, the detection of emission lines allowed to provide hints on the overall properties of the gas in the host galaxies. Even though we warn that we are dealing with a very small sample, we remark that the redshift determination efficiency of our campaign is higher than for previous campaigns. We argue that it is mainly the result of the comparatively higher resolution of X-shooter.

  • 247.
    Prokhorov, Dmitry
    Max Planck Inst Astrophys, Germany.
    An analysis of Fermi-LAT observations of the outskirts of the Coma cluster of galaxies2014Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 441, nr 3, s. 2309-2315Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyse the data from the Fermi-Large Area Telescope in order to search for a ring-like gamma-ray structure around the Coma cluster. The ring-like structure has recently been suggested to be detected with VERITAS at energies higher than 220 GeV and could possibly be associated with an accretion shock. Our analysis of the Fermi data is performed at energies > 100 MeV and we find no detection of this structure in the Fermi data. We derive the 95 per cent upper limit on the flux from the region covering the proposed ring-like structure. The derived upper limit on the flux at > 100 MeV cannot be incorporated with the detection of an accretion shock wave around Coma at the significance of 4.5 sigma by VERITAS at very high energies, if the production mechanism of the gamma-ray emission generates a photon spectrum with a power index of 2 in the broad energy band. The model of gamma-ray emission induced by ultrahigh-energy protons can reconcile the results of the VERITAS and Fermi observations.

  • 248.
    Prokhorov, Dmitry
    Univ Paris 06, CNRS, France ; Moscow Phys Tech Inst, Russia.
    Missing baryons in shells around galaxy clusters2008Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 492, nr 3, s. 651-656Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The cluster baryon fraction is estimated from the CMB-scattering leptonic component of the intracluster medium (ICM); however, the observed cluster baryon fraction is less than the cosmic one. Understanding the origin of this discrepancy is necessary for correctly describing the structure of the ICM. Methods. We estimate the baryonic mass in the outskirts of galaxy clusters which is difficult to observe because of low electron temperature and density in these regions. Results. The time scale for the electrons and protons to reach equipartition in the outskirts is longer than the cluster age. Since thermal equilibrium is not achieved, a significant fraction of the ICM baryons may be hidden in shells around galaxy clusters. We derive the necessary condition on the cluster mass for the concealment of missing baryons in an outer baryon shell and show that this condition is fulfilled because cluster masses are comparable to the estimated characteristic mass M = e(4)/(m(p)(3)G(2)) = 1.3 x 10(15) solar masses. The existence of extreme-ultraviolet emission haloes around galaxy clusters is predicted.

  • 249.
    Prokhorov, Dmitry
    Univ Paris 06, France ; CNRS, France ; Korea Astron & Space Sci Inst, South Korea.
    Non-equilibrium ionization states in galaxy clusters2010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 509, artikel-id A29Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. X-ray imaging observatories have revealed hydrodynamic structures with linear scales of similar to 10 kpc in clusters of galaxies, such as shock waves in the 1E0657-56 and A520 galaxy clusters and the hot plasma bubble in the MKW 3s cluster. The future X-ray observatory IXO will for the first time resolve the metal distribution in galaxy clusters at the these scales. Aims. Heating of plasmas by shocks and AGN activities can result in non-equilibrium ionization states of metal ions. We study the effect of the non-equilibrium ionization at linear scales of less than or similar to 50 kpc in galaxy clusters. Methods. A condition for non-equilibrium ionization is derived by comparing the ionization time-scale with the age of hydrodynamic structures. Modeling of non-equilibrium ionization is performed at a point in time when the plasma temperature suddenly changes. An analysis of the relaxation processes of the FeXXV and FeXXVI ions by means of eigenvectors of the transition matrix is given. Results. We conclude that the non-equilibrium ionization of iron can occur in galaxy clusters if the baryonic overdensity delta is smaller than 11.0/tau, where tau << 1 is the ratio of the hydrodynamic structure age to the Hubble time. Our modeling indicates that the emissivity in the helium-like emission lines of iron increases as a result of the deviation from the ionization equilibrium. A slow process of helium-like ionic fraction relaxation was analyzed. A new way to determine a shock velocity is proposed.

  • 250.
    Prokhorov, Dmitry
    Univ Paris 06, CNRS, France ; Moscow Inst Phys & Technol, Russia.
    On the influence of high energy electron populations on metal abundance estimates in galaxy groups and clusters2009Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 508, nr 1, s. 69-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. Spectral line emissivities have usually been calculated for a Maxwellian electron distribution. But many theoretical works on both galaxy groups and clusters and the solar corona consider modified Maxwellian electron distribution functions when fitting observed X-ray spectra. Here we examine the influence of high energy electron populations on measurements of metal abundances. Methods. A generalized approach proposed by ourselves is used to calculate the line emissivities for a modified Maxwellian distribution. We study metal abundances in galaxy groups and clusters in which hard X-ray excess emission was observed. Results. We found that for modified Maxwellian distributions the argon abundance decreases for the HCG 62 group, the iron abundance decreases for the Centaurus cluster, and the oxygen abundance decreases for the solar corona with respect to the case of a Maxwellian distribution. Therefore, metal abundance measurements are a promising tool for testing the presence of high energy electron populations.

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