lnu.sePublications
Change search
Refine search result
4567 301 - 327 of 327
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 301.
    Thoudam, Satyendra
    et al.
    Radboud University Nijmegen, The Netherlands.
    Buitink, S.
    Vrije Universiteit Brussel.
    Corstanje, A.
    Radboud University Nijmegen, The Netherlands.
    Enriquez, J. E.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; NIKHEF, Science Park Amsterdam, The Netherlands ; Netherlands Institute of Radio Astronomy (ASTRON), The Netherlands .
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands ; NIKHEF, Science Park Amsterdam, The Netherlands.
    Nelles, A.
    Radboud University Nijmegen, The Netherlands ; University of California Irvine, USA.
    Rachen, J. P.
    Radboud University Nijmegen, The Netherlands.
    Rossetto, L.
    Radboud University Nijmegen, The Netherlands.
    Schellart, P.
    Radboud University Nijmegen, The Netherlands.
    Scholten, O.
    University Groningen, The Netherlands.
    ter Veen, S.
    Radboud University Nijmegen, The Netherlands.
    Trinh, T. N. G.
    University Groningen, The Netherlands.
    van Kessel, L.
    Radboud University Nijmegen, The Netherlands.
    Measurement of the cosmic-ray energy spectrum above 1016 eV with the LOFAR Radboud Air Shower Array2016In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 73, p. 34-43Article in journal (Refereed)
    Abstract [en]

    The energy reconstruction of extensive air showers measured with the LOFAR Radboud Air Shower Array (LORA) is presented in detail. LORA is a particle detector array located in the center of the LOFAR radio telescope in the Netherlands. The aim of this work is to provide an accurate and independent energy measurement for the air showers measured through their radio signal with the LOFAR antennas. The energy reconstruction is performed using a parameterized relation between the measured shower size and the cosmic-ray energy obtained from air shower simulations. In order to illustrate the capabilities of LORA, the all-particle cosmic-ray energy spectrum has been reconstructed, assuming that cosmic rays are composed only of protons or iron nuclei in the energy range between ∼2 × 1016 and 2 × 1018 eV. The results are compatible with literature values and a changing mass composition in the transition region from a Galactic to an extragalactic origin of cosmic rays.

  • 302.
    Thoudam, Satyendra
    et al.
    Radboud University Nijmegen, The Netherlands.
    Hörandel, Jörg
    Science Park Amsterdam, The Netherlands.
    Anomaly in the cosmic-ray energy spectrum at GeV-TeV energies2015In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 632, no 1Article in journal (Refereed)
    Abstract [en]

    Recent measurements of cosmic rays by various experiments have found that the energy spectrum of cosmic rays is harder in the TeV region than at GeV energies. The origin of the spectral hardening is not clearly understood. In this paper, we discuss the possibility that the spectral hardening might be due to the effect of re-acceleration of cosmic rays by weak shocks associated with old supernova remnants in the Galaxy.

  • 303.
    Thoudam, Satyendra
    et al.
    Radboud University Nijmegen, The Netherlands.
    Hörandel, Jörg R.
    Radboud University Nijmegen, The Netherlands.
    A possible correlation between the high-energy electron spectrum and the cosmic ray secondary-to-primary ratios2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 414, p. 1432-1438Article in journal (Refereed)
    Abstract [en]

    Recent observations of high-energy cosmic ray electrons by the Fermi-Large Area Telescope (LAT) and the High Energy Stereoscopic System (HESS) experiments between 20 GeV and 5 TeV have found that the energy spectrum closely follows a broken power law with a break at around 1 TeV. On the other hand, measurements of cosmic ray secondary-to-primary ratios like the boron-to-carbon ratio seem to indicate a possible change in the slope at energies around 100 GeV n−1. In this paper, we discuss one possible explanation for the observed break in the electron spectrum and its possible correlation with the flattening in the secondary-to-primary ratios at higher energies. In our model, we assume that cosmic rays after acceleration by supernova remnant shock waves, escape downstream of the shock and remain confined within the remnant until the shock slows down. During this time, the high-energy electrons suffer from radiative energy losses and the cosmic ray nuclei undergo nuclear fragmentations due to their interactions with the matter. Once the cosmic rays are released from the supernova remnants, they follow diffusive propagation in the Galaxy where they further suffer from radiative or fragmentation losses.

  • 304.
    Thoudam, Satyendra
    et al.
    Radboud University Nijmegen, The Netherlands.
    Hörandel, Jörg R
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Cosmic-ray spectral anomaly at GeV-TeV energies as due to re-acceleration by weak shocks in the Galaxy2013In: Proceedings of the 33rd International Cosmic Rays Conference: The Astroparticle Physics Conference, 2013, p. 1-4Conference paper (Refereed)
    Abstract [en]

    Recent cosmic-ray measurements by the ATIC, CREAM and PAMELA experiments have found an apparent hardening of the energy spectrum at TeV energies. Although the origin of the hardening is not clearly understood, possible explanations include hardening in the cosmic-ray source spectrum, changes in the cosmic-ray propagation properties in the Galaxy and the effect of nearby sources. In this contribution, we propose that the spectral anomaly might be an effect of re-acceleration of cosmic rays by weak shocks in the Galaxy. After acceleration by strong supernova remnant shock waves, cosmic rays undergo diffusive propagation through the Galaxy. During the propagation, cosmic rays may again encounter expanding supernova remnant shock waves, and get re-accelerated. As the probability of encountering old supernova remnants is expected to be larger than the young ones due to their bigger size, re-acceleration is expected to be produced mainly by weaker shocks. Since weaker shocks generate a softer particle spectrum, the resulting re-accelerated component will have a spectrum steeper than the initial cosmic-ray source spectrum produced by strong shocks. For a reasonable set of model parameters, it is shown that such re-accelerated component can dominate the GeV energy region while the non-reaccelerated component dominates at higher energies, explaining the observed GeV-TeV spectral anomaly.

  • 305.
    Thoudam, Satyendra
    et al.
    Radboud University Nijmegen, The Netherlands.
    Hörandel, Jörg R.
    Radboud University Nijmegen, The Netherlands.
    GeV-TeV cosmic-ray spectral anomaly as due to reacceleration by weak shocks in the Galaxy2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 567, p. 1-10, article id A33Article in journal (Refereed)
    Abstract [en]

    Recent cosmic-ray measurements have found an anomaly in the cosmic-ray energy spectrum at GeV-TeV energies. Although the origin of the anomaly is not clearly understood, suggested explanations include the effect of cosmic-ray source spectrum, propagation effects, and the effect of nearby sources. In this paper, we propose that the spectral anomaly might be an effect of reacceleration of cosmic rays by weak shocks in the Galaxy. After acceleration by strong supernova remnant shock waves, cosmic rays undergo diffusive propagation through the Galaxy. During the propagation, cosmic rays may again encounter expanding supernova remnant shock waves, and get re-accelerated. As the probability of encountering old supernova remnants is expected to be larger than the younger remnants because of their bigger sizes, reacceleration is expected to be produced mainly by weaker shocks. Since weaker shocks generate a softer particle spectrum, the resulting re-accelerated component will have a spectrum steeper than the initial cosmic-ray source spectrum produced by strong shocks. For a reasonable set of model parameters, it is shown that the re-accelerated component can dominate the GeV energy region while the non-reaccelerated component dominates at higher energies, thereby explaining the observed GeV-TeV spectral anomaly.

  • 306.
    Thoudam, Satyendra
    et al.
    Radboud University Nijmegen, The Netherlands.
    Hörandel, Jörg R.
    Radboud University Nijmegen, The Netherlands.
    Nearby supernova remnants and the cosmic ray spectral hardening at high energies2012In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 421, no 2, p. 1209-1214Article in journal (Refereed)
    Abstract [en]

    Recent measurements of cosmic ray spectra of several individual nuclear species by the CREAM, TRACER and ATIC experiments indicate a change in the spectral index of the power laws at TeV energies. Possible explanations among others include non-linear diffusive shock acceleration of cosmic rays, different cosmic ray propagation properties at higher and lower energies in the Galaxy and the presence of nearby sources. In this paper, we show that if supernova remnants are the main sources of cosmic rays in our Galaxy, the effect of the nearby remnants can be responsible for the observed spectral changes. Using a rigidity-dependent escape of cosmic rays from the supernova remnants, we explain the apparent observed property that the hardening of the helium spectrum occurs at relatively lower energies as compared to the protons and also that the spectral hardening does not persist beyond ∼(20–30) TeV energies.

  • 307.
    Thoudam, Satyendra
    et al.
    Radboud University Nijmegen, The Netherlands.
    Hörandel, Jörg R.
    Radboud University Nijmegen, The Netherlands.
    On the point-source approximation of nearby cosmic ray sources2012In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 419, no 1, p. 624-637Article in journal (Refereed)
    Abstract [en]

    In this paper, we check in detail the validity of the widely adopted point-source approximation for nearby cosmic ray (CR) sources. Under an energy-independent escape model for CRs from the sources, we show that for young nearby sources, the point-source approximation breaks down at lower energies and the CR spectrum depends on the size and the morphology of the source. When applied to the nearby supernova remnants (SNRs), we find that the approximation breaks down for some of the individual remnants like the Vela, but interestingly it still holds good for their combined total spectrum at the Earth. Moreover, we also find that the results obtained under this simple approximation are quite different from those calculated under an energy-dependent escape model which is favoured by diffusive shock acceleration models inside SNRs. Our study suggests that if SNRs are the main sources of CRs in our Galaxy, then the commonly adopted point-source model (with an energy-independent escape scenario) appears flawed for CR studies from the nearby SNRs.

  • 308.
    Thoudam, Satyendra
    et al.
    Radboud University Nijmegen, The Netherlands.
    Hörandel, Jörg R.
    Radboud University Nijmegen, The Netherlands.
    Revisiting the hardening of the cosmic ray energy spectrum at TeV energies2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 435, no 3, p. 2532-2542Article in journal (Refereed)
    Abstract [en]

    Measurements of cosmic rays by experiments such as ATIC, CREAM and PAMELA indicate a hardening of the cosmic ray energy spectrum at TeV energies. In our recent work, we showed that the hardening can be due to the effect of nearby supernova remnants. We showed it for the case of protons and helium nuclei. In this paper, we present an improved and more detailed version of our previous work, and extend our study to heavier cosmic ray species such as boron, carbon, oxygen and iron nuclei. Unlike our previous study, the present work involves a detailed calculation of the background cosmic rays and follows a consistent treatment of cosmic ray source parameters between the background and the nearby components. Moreover, we also present a detailed comparison of our results on the secondary-to-primary ratios, secondary spectra and the diffuse gamma-ray spectrum with the results expected from other existing models, which can be checked by future measurements at high energies.

  • 309.
    Thoudam, Satyendra
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Radboud Univ Nijmegen, Netherlands.
    Rachen, J. P.
    Radboud Univ Nijmegen, Netherlands.
    van Vliet, A.
    Radboud Univ Nijmegen, Netherlands.
    Achterberg, A.
    Radboud Univ Nijmegen, Netherlands.
    Buitink, S.
    Vrije Univ Brussel, Belgium.
    Falcke, H.
    Radboud Univ Nijmegen, Netherlands ; NIKHEF, Netherlands ; ASTRON, Netherlands.
    Horandel, J. R.
    Radboud Univ Nijmegen, Netherlands ; NIKHEF, Netherlands.
    Cosmic-ray energy spectrum and composition up to the ankle: the case for a second Galactic component2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 595, article id A33Article in journal (Refereed)
    Abstract [en]

    Motivated by the recent high-precision measurements of cosmic rays by several new-generation experiments, we have carried out a detailed study to understand the observed energy spectrum and composition of cosmic rays with energies up to about 10(18) eV. Our study shows that a single Galactic component with subsequent energy cut-offs in the individual spectra of different elements, optimised to explain the observed elemental spectra below similar to 10(14) eV and the "knee" in the all-particle spectrum, cannot explain the observed all-particle spectrum above similar to 2 x 10(16) eV. We discuss two approaches for a second component of Galactic cosmic rays re-acceleration at a Galactic wind termination shock, and supernova explosions of Wolf-Rayet stars, and show that the latter scenario can explain almost all observed features in the all-particle spectrum and the composition up to similar to 10(18) eV, when combined with a canonical extra-galactic spectrum expected from strong radio galaxies or a source population with similar cosmological evolution. In this two-component Galactic model, the knee at similar to 3 x 10(15) eV and the "second knee" at similar to 10(17) eV in the all-particle spectrum are due to the cut-offs in the first and second components, respectively. We also discuss several variations of the extra-galactic component, from a minimal contribution to scenarios with a significant component below the "ankle" (at similar to 4 x 10(18) eV), and find that extragalactic contributions in excess of regular source evolution are neither indicated nor in conflict with the existing data. We also provide arguments that an extra-galactic contribution is unlikely to dominate at or below the second knee. Our main result is that the second Galactic component predicts a composition of Galactic cosmic rays at and above the second knee that largely consists of helium or a mixture of helium and CNO nuclei, with a weak or essentially vanishing iron fraction, in contrast to most common assumptions. This prediction is in agreement with new measurements from LOFAR and the Pierre Auger Observatory which indicate a strong light component and a rather low iron fraction between similar to 10(17) and 10(18) eV.

  • 310.
    Thoudam, Satyendra
    et al.
    Bhabha Atomic Research Centre, India.
    Yadav, K. K.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Sahayanathan, S.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    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.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Godambe, S.
    Bhabha Atomic Research Centre, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    VHE Observations of H1426+428 using TACTIC imaging telescope: 20042005In: 29th International Cosmic Ray Conference Pune (2005), 2005, Vol. 4, p. 363-366Conference paper (Refereed)
  • 311.
    Tickoo, A. K.
    et al.
    Bhabha Atomic Research Centre.
    Suthar, R. L.
    Bhabha Atomic Research Centre.
    Koul, R.
    Bhabha Atomic Research Centre.
    Sapru, M. L.
    Bhabha Atomic Research Centre.
    Kumar, N.
    Bhabha Atomic Research Centre.
    Kaul, C. L.
    Bhabha Atomic Research Centre.
    Yadav, K. K.
    Bhabha Atomic Research Centre.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre.
    Kaul, S. K.
    Bhabha Atomic Research Centre.
    Venugopal, K.
    Bhabha Atomic Research Centre.
    Kothari, M.
    Bhabha Atomic Research Centre.
    Goyal, H. C.
    Bhabha Atomic Research Centre.
    Chandra, P.
    Bhabha Atomic Research Centre.
    Dhar, V. K.
    Bhabha Atomic Research Centre.
    Rannot, R. C.
    Bhabha Atomic Research Centre.
    Koul, M. K.
    Bhabha Atomic Research Centre.
    Kaul, S. R.
    Bhabha Atomic Research Centre.
    A generalized ray-tracing procedure for an atmospheric Cherenkov imaging telescope and optical characteristics of the TACTIC light collector2005In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 539, no 1-2, p. 177-190Article in journal (Refereed)
    Abstract [en]

    A generalized ray-tracing procedure has been developed, which facilitates the design of a multimirror-based light collector used in atmospheric Cherenkov telescopes. This procedure has been employed to study the optical characteristics of the 3.5 m diameter light collector of the TACTIC Imaging telescope. Comparison of the measured point-spread function of the light collector with the simulated performance of ideal Davies–Cotton and paraboloid designs has been made to determine an optimum arrangement of the 34 spherical mirror facets used in the telescope to obtain the best possible point-spread function. A description of the ray-tracing subroutine used for processing CORSIKA-generated Cherenkov data, required for carrying out Monte-Carlo simulation studies, is also discussed in the paper.

  • 312. Togo, V
    et al.
    Ambrosio, M
    Antolini, R
    Auriemma, G
    Bakari, D
    Baldini, A
    Barbarino, G C
    Barish, B C
    Battistoni, G
    Becherini, Yvonne
    Bellotti, R
    Bemporad, C
    Bernardini, P
    Bilokon, H
    Bloise, C
    Bower, C
    Brigida, M
    Bussino, S
    Cafagna, F
    Campana, D
    Carboni, M
    Caruso, R
    Cecchini, S
    Cei, F
    Chiarella, V
    Chiarusi, T
    Choudhary, B C
    Coutu, S
    Cozzi, M
    De Cataldo, G
    Dekhissi, H
    De Marzo, C
    Erriquez, O
    Favuzzi, C
    Forti, C
    Fusco, P
    Giacomelli, G
    Giannini, G
    Giglietto, N
    Giorgini, M
    Grassi, M
    Grillo, A
    Guarino, F
    Gustavino, C
    Habig, A
    Hanson, K
    Heinz, R
    Iarocci, E
    Katsavounidis, E
    Katsavounidis, I
    Kearns, E
    Kim, H
    Kyriazopoulou, S
    Kumar, A
    Lamanna, E
    Lane, C
    Levin, D S
    Lipari, P
    Longo, M J
    Loparco, F
    Maaroufi, F
    Mancarella, G
    Mandrioli, G
    Manzoor, S
    Margiotta, A
    Marini, A
    Martello, D
    Marzari-Chiesa, A
    Matteuzzi, D
    Michael, D G
    Monacelli, P
    Montaruli, T
    Monteno, M
    Mufson, S
    Musser, J
    Nicolo, D
    Nolty, R
    Orth, C
    Osteria, G
    Palamara, O
    Patera, V
    Patrizii, L
    Pazzi, R
    Peck, C W
    Perrone, L
    Petrera, S
    Pistilli, P
    Popa, V
    Raino, A
    Reynoldson, J
    Ronga, F
    Rrhioua, A
    Satriano, C
    Scapparone, E
    Scholberg, K
    Sciubba, A
    Serra, P
    Sioli, M
    Sirri, G
    Sitta, M
    Spinelli, P
    Spinetti, M
    Spurio, M
    Steinberg, R
    Stone, J L
    Sulak, L R
    Surdo, A
    G, Tarle
    Vakili, M
    Walter, C W
    Webb, R
    Calibrations of CR39 and Makrofol nuclear track detectors and search for exotic particles2003In: Nuclear physics B, Proceedings supplements, ISSN 0920-5632, E-ISSN 1873-3832, Vol. 125, p. 217-221Article in journal (Refereed)
    Abstract [en]

    We present the final results of the search for exotic massive particles in the cosmic radiation performed with the MACRO underground experiment. Magnetic monopoles and nuclearites flux upper limits obtained with the CR39 nuclear track subdetector, the scintillation and streamer tube subdetectors are given. Searches at high altitude with the SLIM experiment are in progress.

  • 313.
    Trinh, T. N. G.
    et al.
    University Groningen, The Netherlands.
    Scholten, O.
    University Groningen, The Netherlands ; Vrije Universiteit Brussel, The Netherlands.
    Buitink, S.
    Vrije Universiteit Brussel, The Netherlands ; Radboud University Nijmegen, The Netherlands.
    van den Berg, A. M.
    University Groningen, The Netherlands.
    Corstanje, A.
    Radboud University Nijmegen, The Netherlands.
    Ebert, U.
    Center for Mathematics and Computer Science (CWI), The Netherlands ; Eindhoven University of Technology, The Netherlands.
    Enriquez, J. E.
    Radboud University Nijmegen, The Netherlands.
    Falcke, H.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands ; ASTRON, The Netherlands ; Max Planck Institute for Radio Astronomy, Germany.
    Hörandel, J. R.
    Radboud University Nijmegen, The Netherlands ; Science Park Amsterdam, The Netherlands.
    Köhn, C.
    Technical University of Denmark, Denmark.
    Nelles, A.
    Rachen, J. P.
    Rossetto, L.
    Rutjes, C.
    Schellart, P.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    ter Veen, S.
    de Vries, K. D.
    Influence of atmospheric electric fields on the radio emission from extensive air showers2016In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 93, no 2, article id 023003Article in journal (Refereed)
    Abstract [en]

    The atmospheric electric fields in thunderclouds have been shown to significantly modify the intensity and polarization patterns of the radio footprint of cosmic-ray-induced extensive air showers. Simulations indicated a very nonlinear dependence of the signal strength in the frequency window of 30–80 MHz on the magnitude of the atmospheric electric field. In this work we present an explanation of this dependence based on Monte Carlo simulations, supported by arguments based on electron dynamics in air showers and expressed in terms of a simplified model. We show that by extending the frequency window to lower frequencies, additional sensitivity to the atmospheric electric field is obtained.

  • 314.
    Tsivras, Sotirios-Ilias
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    ALTO Timing Calibration: Calibration of the ALTO detector array based on cosmic-ray simulations2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis describes a timing calibration method for the detector array of the ALTO experiment. ALTO is a project currently at the prototype phase that aims to build a gamma-ray astronomical observatory at high-altitude in the Southern hemisphere. ALTO can be assumed as a hybrid system as each detector consists of a Water Cherenkov Detector (WCD) on top of a Scintillator Detector (SD), providing an increased signal to background discrimination compared to other WCD arrays.

    ALTO is planned to complement the Very-High-Energy (VHE) observations by the High Altitude Water Cherenkov (HAWC) gamma ray observatory that collects data from the Northern sky. By the time the full array of 1242 detectors is installed to the proposed site, ALTO together with HAWC and the future Cherenkov Telescope Array (CTA) will serve as a state-of-the-art detection system for VHE gamma-rays combining the WCD and the Imaging Atmospheric Cherenkov Telescope (IACT) techniques.

    When a VHE gamma-ray or cosmic-ray enters the Earth’s atmosphere, it initiates an Extensive Air Shower (EAS). These particles are sampled by the detector array and by checking the arrival times of nearby tanks, the method reveals whether a detector suffers from a time-offset.

    The data analyzed in this thesis derive from CORSIKA (COsmic Ray SImulation for KAscade) and GEANT4 (GEometry ANd Tracking) simulations of cosmic-ray events within the energy range of 1–1:6TeV, which mainly consist of protons. The high flux of this particular type of cosmic-rays, gives us a tool to statistically evaluate the results generated by the proposed timing calibration method.

    In the framework of this thesis, I have written code in Python programming language in order to develop the timing calibration method. The method identifies detectors that suffer from time-offsets and improves the reconstruction accuracy of the ALTO detector array. Different Python packages were used to execute different tasks: astropy to read filter-present-write large datasets, numpy (Numerical Python) to make datasets comprehensiveto functions, scipy (Scientific Python) to develop our models, sympy (Symbolic Python) to find geometrical correlations and matplotlib (Mathematical Plotting Library) to draw figures and diagrams.

    The current version of the method achieves sub-nanosecond accuracy. The next stepis to make the timing calibration more intelligent in order to correct itself. This self correction includes an agile adaptation to the data acquired for long periods of time, in order to make different compromises at different time intervals.

    Download full text (pdf)
    ALTO Timing Calibration
  • 315.
    Valtonen-Mattila, Nora
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    High Energy gamma-ray behavior of a potential astrophysical neutrino source: The case of TXS 0506+0562019Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    Blazars are a type of Active Galaxy that emit strong astrophysical jets. The association of a HE gamma-ray flare from the blazar TXS 0506+056 to the IceCube-170922A neutrino event in 2017, opened the possibility to a link between these two events. In this thesis, we will look at the HE gamma-ray behavior of TXS 0506+056 using data obtained from the Fermi-LAT by taking into account the other set of neutrino events associated with this source from 2014-2015. We will investigate whether both neutrino events present with comparable HE gamma-ray behavior by analyzing the lightcurves and the spectra for a quiet state, the 2014-2015 period, and the flare centered around the neutrino event from 2017. The results of the analysis performed in this thesis show no strong indication of a change in the gamma-ray behaviour in these potential neutrino detections.

    Download full text (pdf)
    High Energy gamma-ray behavior of a potential astrophysical neutrino source
  • 316. van Haarlem, M. P.
    et al.
    Wise, M. W.
    Gunst, A. W.
    Heald, G.
    McKean, J. P.
    Hessels, J. W. T.
    de Bruyn, A. G.
    Nijboer, R.
    Swinbank, J.
    Fallows, R.
    Brentjens, M.
    Nelles, A.
    Beck, R.
    Falcke, H.
    Fender, R.
    Hörandel, J.
    Koopmans, L. V. E.
    Mann, G.
    Miley, G.
    Röttgering, H.
    Stappers, B. W.
    Wijers, R. A. M. J.
    Zaroubi, S.
    van den Akker, M.
    Alexov, A.
    Anderson, J.
    Anderson, K.
    van Ardenne, A.
    Arts, M.
    Asgekar, A.
    Avruch, I. M.
    Batejat, F.
    Bähren, L.
    Bell, M. E.
    Bell, M. R.
    van Bemmel, I.
    Bennema, P.
    Bentum, M. J.
    Bernardi, G.
    Best, P.
    Bîrzan, L.
    Bonafede, A.
    Boonstra, A. -J
    Braun, R.
    Bregman, J.
    Breitling, F.
    van de Brink, R. H.
    Broderick, J.
    Broekema, P. C.
    Brouw, W. N.
    Brüggen, M.
    Butcher, H. R.
    van Cappellen, W.
    Ciardi, B.
    Coenen, T.
    Conway, J.
    Coolen, A.
    Corstanje, A.
    Damstra, S.
    Davies, O.
    Deller, A. T.
    Dettmar, R. -J
    van Diepen, G.
    Dijkstra, K.
    Donker, P.
    Doorduin, A.
    Dromer, J.
    Drost, M.
    van Duin, A.
    Eislöffel, J.
    van Enst, J.
    Ferrari, C.
    Frieswijk, W.
    Gankema, H.
    Garrett, M. A.
    de Gasperin, F.
    Gerbers, M.
    de Geus, E.
    Grießmeier, J. -M
    Grit, T.
    Gruppen, P.
    Hamaker, J. P.
    Hassall, T.
    Hoeft, M.
    Holties, H. A.
    Horneffer, A.
    van der Horst, A.
    van Houwelingen, A.
    Huijgen, A.
    Iacobelli, M.
    Intema, H.
    Jackson, N.
    Jelic, V.
    de Jong, A.
    Juette, E.
    Kant, D.
    Karastergiou, A.
    Koers, A.
    Kollen, H.
    Kondratiev, V. I.
    Kooistra, E.
    Koopman, Y.
    Koster, A.
    Kuniyoshi, M.
    Kramer, M.
    Kuper, G.
    Lambropoulos, P.
    Law, C.
    van Leeuwen, J.
    Lemaitre, J.
    Loose, M.
    Maat, P.
    Macario, G.
    Markoff, S.
    Masters, J.
    McFadden, R. A.
    McKay-Bukowski, D.
    Meijering, H.
    Meulman, H.
    Mevius, M.
    Middelberg, E.
    Millenaar, R.
    Miller-Jones, J. C. A.
    Mohan, R. N.
    Mol, J. D.
    Morawietz, J.
    Morganti, R.
    Mulcahy, D. D.
    Mulder, E.
    Munk, H.
    Nieuwenhuis, L.
    van Nieuwpoort, R.
    Noordam, J. E.
    Norden, M.
    Noutsos, A.
    Offringa, A. R.
    Olofsson, H.
    Omar, A.
    Orrú, E.
    Overeem, R.
    Paas, H.
    Pandey-Pommier, M.
    Pandey, V. N.
    Pizzo, R.
    Polatidis, A.
    Rafferty, D.
    Rawlings, S.
    Reich, W.
    de Reijer, J. -P
    Reitsma, J.
    Renting, G. A.
    Riemers, P.
    Rol, E.
    Romein, J. W.
    Roosjen, J.
    Ruiter, M.
    Scaife, A.
    van der Schaaf, K.
    Scheers, B.
    Schellart, P.
    Schoenmakers, A.
    Schoonderbeek, G.
    Serylak, M.
    Shulevski, A.
    Sluman, J.
    Smirnov, O.
    Sobey, C.
    Spreeuw, H.
    Steinmetz, M.
    Sterks, C. G. M.
    Stiepel, H. -J
    Stuurwold, K.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    Thomas, I.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, M. C.
    van der Tol, B.
    Usov, O.
    van Veelen, M.
    van der Veen, A. -J
    ter Veen, S.
    Verbiest, J. P. W.
    Vermeulen, R.
    Vermaas, N.
    Vocks, C.
    Vogt, C.
    de Vos, M.
    van der Wal, E.
    van Weeren, R.
    Weggemans, H.
    Weltevrede, P.
    White, S.
    Wijnholds, S. J.
    Wilhelmsson, T.
    Wucknitz, O.
    Yatawatta, S.
    Zarka, P.
    Zensus, A.
    van Zwieten, J.
    LOFAR: The LOw-Frequency ARray2013In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 556, p. 1-53, article id A2Article in journal (Refereed)
    Abstract [en]

    LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10–240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR’s new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.

  • 317. van Weeren, R. J.
    et al.
    Williams, W. L.
    Tasse, C.
    Röttgering, H. J. A.
    Rafferty, D. A.
    van der Tol, S.
    Heald, G.
    White, G. J.
    Shulevski, A.
    Best, P.
    Intema, H. T.
    Bhatnagar, S.
    Reich, W.
    Steinmetz, M.
    van Velzen, S.
    Enßlin, T. A.
    Prandoni, I.
    de Gasperin, F.
    Jamrozy, M.
    Brunetti, G.
    Jarvis, M. J.
    McKean, J. P.
    Wise, M. W.
    Ferrari, C.
    Harwood, J.
    Oonk, J. B. R.
    Hoeft, M.
    Kunert-Bajraszewska, M.
    Horellou, C.
    Wucknitz, O.
    Bonafede, A.
    Mohan, N. R.
    Scaife, A. M. M.
    Klöckner, H. -R
    van Bemmel, I. M.
    Merloni, A.
    Chyzy, K. T.
    Engels, D.
    Falcke, H.
    Pandey-Pommier, M.
    Alexov, A.
    Anderson, J.
    Avruch, I. M.
    Beck, R.
    Bell, M. E.
    Bentum, M. J.
    Bernardi, G.
    Breitling, F.
    Broderick, J.
    Brouw, W. N.
    Brüggen, M.
    Butcher, H. R.
    Ciardi, B.
    de Geus, E.
    de Vos, M.
    Deller, A.
    Duscha, S.
    Eislöffel, J.
    Fallows, R. A.
    Frieswijk, W.
    Garrett, M. A.
    Grießmeier, J.
    Gunst, A. W.
    Hamaker, J. P.
    Hassall, T. E.
    Hörandel, J.
    van der Horst, A.
    Iacobelli, M.
    Jackson, N. J.
    Juette, E.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Maat, P.
    Mann, G.
    McKay-Bukowski, D.
    Mevius, M.
    Morganti, R.
    Munk, H.
    Offringa, A. R.
    Orrù, E.
    Paas, H.
    Pandey, V. N.
    Pietka, G.
    Pizzo, R.
    Polatidis, A. G.
    Renting, A.
    Rowlinson, A.
    Schwarz, D.
    Serylak, M.
    Sluman, J.
    Smirnov, O.
    Stappers, B. W.
    Stewart, A.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, C.
    Vermeulen, R.
    Vocks, C.
    Zarka, P.
    LOFAR Low-band Antenna Observations of the 3C 295 and Boötes Fields: Source Counts and Ultra-steep Spectrum Sources2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 793, no 82, p. 1-22Article in journal (Refereed)
    Abstract [en]

    We present Low Frequency Array (LOFAR) Low Band observations of the Boötes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam–1, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17-52 deg2. From the observations, we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and Very Large Array 74 MHz differential source counts, scaling with a spectral index of –0.7. We find that a spectral index scaling of –0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens toward lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum (α < –1.1) radio sources that could be associated with massive high-redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Boötes field. We cross-correlate these radio sources with optical and infrared catalogs and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the 0.7 z 2.5 range.

  • 318. Vedantham, H. K.
    et al.
    Koopmans, L. V. E.
    de Bruyn, A. G.
    Wijnholds, S. J.
    Brentjens, M.
    Abdalla, F. B.
    Asad, K. M. B.
    Bernardi, G.
    Bus, S.
    Chapman, E.
    Ciardi, B.
    Daiboo, S.
    Fernandez, E. R.
    Ghosh, A.
    Harker, G.
    Jelic, V.
    Jensen, H.
    Kazemi, S.
    Lambropoulos, P.
    Martinez-Rubi, O.
    Mellema, G.
    Mevius, M.
    Offringa, A. R.
    Pandey, V. N.
    Patil, A. H.
    Thomas, R. M.
    Veligatla, V.
    Yatawatta, S.
    Zaroubi, S.
    Anderson, J.
    Asgekar, A.
    Bell, M. E.
    Bentum, M. J.
    Best, P.
    Bonafede, A.
    Breitling, F.
    Broderick, J.
    Brüggen, M.
    Butcher, H. R.
    Corstanje, A.
    de Gasperin, F.
    de Geus, E.
    Deller, A.
    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.
    Hassall, T. E.
    Heald, G.
    Hoeft, M.
    Hörandel, J.
    Iacobelli, M.
    Juette, E.
    Kondratiev, V. I.
    Kuniyoshi, M.
    Kuper, G.
    Mann, G.
    Markoff, S.
    McFadden, R.
    McKay-Bukowski, D.
    McKean, J. P.
    Mulcahy, D. D.
    Munk, H.
    Nelles, A.
    Norden, M. J.
    Orru, E.
    Pandey-Pommier, M.
    Pizzo, R.
    Polatidis, A. G.
    Reich, W.
    Renting, A.
    Röttgering, H.
    Schwarz, D.
    Shulevski, A.
    Smirnov, O.
    Stappers, B. W.
    Steinmetz, M.
    Swinbank, J.
    Tagger, M.
    Tang, Y.
    Tasse, C.
    ter Veen, S.
    Thoudam, Satyendra
    Radboud University Nijmegen, The Netherlands.
    Toribio, C.
    Vocks, C.
    Wise, M. W.
    Wucknitz, O.
    Zarka, P.
    Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 450, p. 2291-2305Article in journal (Refereed)
    Abstract [en]

    We present radio observations of the Moon between 35 and 80 MHz to demonstrate a novel technique of interferometrically measuring large-scale diffuse emission extending far beyond the primary beam (global signal) for the first time. In particular, we show that (i) the Moon appears as a negative-flux source at frequencies 35 < ν < 80 MHz since it is ‘colder’ than the diffuse Galactic background it occults, (ii) using the (negative) flux of the lunar disc, we can reconstruct the spectrum of the diffuse Galactic emission with the lunar thermal emission as a reference, and (iii) that reflected RFI (radio-frequency interference) is concentrated at the centre of the lunar disc due to specular nature of reflection, and can be independently measured. Our RFI measurements show that (i) Moon-based Cosmic Dawn experiments must design for an Earth-isolation of better than 80 dB to achieve an RFI temperature <1 mK, (ii) Moon-reflected RFI contributes to a dipole temperature less than 20 mK for Earth-based Cosmic Dawn experiments, (iii) man-made satellite-reflected RFI temperature exceeds 20 mK if the aggregate scattering cross-section of visible satellites exceeds 175 m2 at 800 km height, or 15 m2 at 400 km height. Currently, our diffuse background spectrum is limited by sidelobe confusion on short baselines (10–15 per cent level). Further refinement of our technique may yield constraints on the redshifted global 21 cm signal from Cosmic Dawn (40 > z > 12) and the Epoch of Reionization (12 > z > 5).

  • 319.
    Weishaupt, Hrafn N. H.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Implementing a pipeline to search for transiting exoplanets: application to the K2 survey data2018Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    The detection of exoplanets has rapidly evolved to one of the most important frontiers of astronomical and astrophysical research. The recent decades have seen the development of various techniques for detecting exoplanets. Of these approaches the transit method has received particular interest and has lead to the largest number of discoveries to date.

    The Kepler K2 mission is an ongoing observational survey, which has generated light curves for thousands of stars, a large fraction of which have yet to be fully explored. To discover and characterize the transiting planets hosted by the respective stars, extensive transit screens are required. However, implementing a pipeline for transit analyses is not straight forward, considering the light curve properties of different survey, the rapid changes brought by technological advancements, and the apparent lack of a golden standard with respect to the applied methodology.

    The project has reviewed several aspects of exoplanet detection via the transit method. Particular focus was placed on the identification of a suitable workflow covering the relevant steps to move from raw light curve files to a final prediction and characterization of transiting planetary candidates. Adhering to the identified strategy, the major part of the project then dealt with the implementation of a pipeline that integrates and executes all the different steps in a streamlined fashion. Of note, primary focus was placed on the actual selection and implementation of methods into an operational pipeline, but due to the given time constraints extensive optimizations of each individual processing step was outside the scope of this project.

    Nevertheless, the pipeline was employed to predict transit candidates for K2 campaigns C7, C8, C10, C11, and C12. A comparsion of the most conservative predictions from campaigns C7 and C10 with previously reported exoplanet candidates demonstrated that the pipeline was highly capable of discovering reliable transit candidates. Since campaigns C11 and C12 have not yet been fully explored, the respective candidates predicted for those campaigns in the current project might thus harbour novel planetary transit candidates that would be suitable for follow-up confirmation runs.

    In summary, the current project has produced a pipeline for performing transiting exoplanet searches in K2 data, which integrates the steps from raw light curve processing to transit candidate selection and characterization. The pipeline has been demonstrated to predict credible transit candidates, but future work will have to focus on additional optimizations of individual method parameters and on the analysis of transit detection efficiencies.

    Download full text (pdf)
    fulltext
  • 320.
    Winchen, T.
    et al.
    Vrije Universiteit Brussel, Belgium.
    Bonardi, A.
    Radboud University, The Netherlands.
    Buitink, S.
    Vrije Universiteit Brussel, Belgium.
    Corstanje, A.
    Radboud University, The Netherlands.
    Falcke, H.
    Radboud University, The Netherlands;NIKHEF, Science Park Amsterdam, The Netherlands;Netherlands Institute of Radio Astronomy (ASTRON), The Netherlands .
    Hare, B. M.
    University Groningen, Germany.
    Hörandel, J. R.
    Radboud University, The Netherlands;NIKHEF, Science Park Amsterdam, The Netherlands.
    Mitra, P.
    Vrije Universiteit Brussel, Belgium.
    Mulrey, K.
    Vrije Universiteit Brussel, Belgium.
    Nelles, A.
    Humboldt-Universität zu Berlin, Germany.
    Rachen, J. P.
    Radboud University, Netherlands.
    Rossetto, L.
    Radboud University, Netherlands.
    Schellart, P.
    Radboud University, Netherlands;Princeton University, USA.
    Scholten, O.
    University Groningen, Germany;Vrije Universiteit Brussel, Belgium.
    Ter Veen, S.
    Radboud University, The Netherlands;Netherlands Institute of Radio Astronomy (ASTRON), The Netherlands.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Radboud University, The Netherlands.
    Trinh, T. N. G.
    University Groningen, Germany.
    Cosmic ray physics with the LOFAR radio telescope2019In: 26th Extended European Cosmic Ray Symposium, 6–10 July 2018, Altai State University, Barnaul-Belokurikha, Russian Federation, Institute of Physics (IOP), 2019, no 1Conference paper (Refereed)
    Abstract [en]

    The LOFAR radio telescope is able to measure the radio emission from cosmic ray induced air showers with hundreds of individual antennas. This allows for precision testing of the emission mechanisms for the radio signal as well as determination of the depth of shower maximum X max , the shower observable most sensitive to the mass of the primary cosmic ray, to better than 20 g cm -2 . With a densely instrumented circular area of roughly 320 m 2 , LOFAR is targeting for cosmic ray astrophysics in the energy range 10 16 -10 18 eV. In this contribution we give an overview of the status, recent results, and future plans of cosmic ray detection with the LOFAR radio telescope. © Published under licence by IOP Publishing Ltd.

  • 321.
    Winchen, T.
    et al.
    Vrije Universiteit Brussel, Belgium.
    Bonardi, A.
    Radboud University, The Netherlands.
    Buitink, S.
    Vrije Universiteit Brussel, Belgium.
    Corstanje, A.
    Radboud University, The Netherlands.
    Falcke, H.
    Radboud University, The Netherlands;Science Park Amsterdam, The Netherlands;Netherlands Institute of Radio Astronomy (ASTRON), The Netherlands.
    Hare, B. M.
    University Groningen, Germany.
    Hörandel, J. R.
    Radboud University, The Netherlands;NIKHEF, Science Park Amsterdam, The Netherlands.
    Mitra, P.
    Vrije Universiteit Brussel, Belgium.
    Mulrey, K.
    Vrije Universiteit Brussel, Belgium.
    Nelles, A.
    Humboldt-Universität zu Berlin, Germany.
    Rachen, J. P.
    Radboud University, The Netherlands.
    Rossetto, L.
    Radboud University, The Netherlands.
    Schellart, P.
    Radboud University, The Netherlands;Princeton University, Princeton, USA.
    Scholten, O.
    University Groningen, Germany;Vrije Universiteit Brussel, Belgium.
    Ter Veen, S.
    Radboud University, The Netherlands; Netherlands Institute of Radio Astronomy (ASTRON), The Netherlands.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Radboud University, The Netherlands.
    Trinh, T. N. G.
    University Groningen, Germany.
    Status of the lunar detection mode for cosmic particles of LOFAR2019In: Journal of Physics: Conference Series, Institute of Physics (IOP), 2019, no 1, article id 012077Conference paper (Refereed)
    Abstract [en]

    Cosmic particles hitting Earth's moon produce radio emission via the Askaryan effect. If the resulting radio ns-pulse can be detected by radio telescopes, this technique potentially increases the available collective area for ZeV scale particles by several orders of magnitude compared to current experiments. The LOw Frequency ARray (LOFAR) is the largest radio telescope operating in the optimum frequency regime for this technique. In this contribution, we report on the status of the implementation of the lunar detection mode at LOFAR. © Published under licence by IOP Publishing Ltd.

  • 322.
    Winchen, Tobias
    et al.
    Vrije Universiteit Brussel, Belgium.
    Bonardi, Antonio
    Radboud University, Netherlands.
    Buitink, Stijn
    Vrije Universiteit Brussel, Belgium.
    Corstanje, Arthur
    Radboud University, Netherlands.
    Falcke, Heino
    Radboud University, Netherlands;Nikhef, Netherlands;Netherlands Institute of Radio Astronomy (ASTRON), Netherlands.
    Hare, Brian M.
    University of Groningen, Netherlands.
    Hörandel, Jörg R.
    Radboud University, Netherlands;Nikhef, Netherlands.
    Mitra, Pragati
    Vrije Universiteit Brussel, Belgium.
    Mulrey, Katharine
    Vrije Universiteit Brussel, Belgium.
    Nelles, Anna
    Radboud University, Netherlands;University of California Irvine, USA.
    Rachen, J. P.
    Rossetto, L.
    Radboud University, Netherlands.
    Schellart, P.
    Radboud University, Netherlands; Princeton University, United States.
    Scholten, O.
    University Groningen, Netherlands;Vrije Universiteit Brussel, Belgium.
    Ter Veen, S.
    Radboud University, Netherlands;Netherlands Institute of Radio Astronomy (ASTRON), Netherlands.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Radboud University, Netherlands.
    Trinh, T. N. G.
    University Groningen, Netherlands.
    Overview and status of the lunar detection of cosmic particles with LOFAR2018In: Proceedings of Science: 35th International Cosmic Ray Conference, ICRC 2017; Bexco, Busan; South Korea; 10-20 July 2017, Sissa Medialab Srl , 2018Conference paper (Refereed)
    Abstract [en]

    When a cosmic particle hits matter it produces radio emission via the Askaryan effect. This allows to use Earth's moon as detector for cosmic particles by searching for these ns-pulses with radio telescopes. This technique potentially increases the available collective area by several orders of magnitude compared to current experiments. The LOw Frequency ARray (LOFAR) is the largest radio telescope operating in the optimum frequency regime for corresponding searches. In this contribution, we report on the design and status of the implementation of the lunar detection mode at LOFAR. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0).

  • 323. Wouters, Denis
    et al.
    Lenain, Jean-Philippe
    Becherini, Yvonne
    University Paris Diderot.
    Harris, Jon
    Brun, Pierre
    Kaufman, Sarah
    Boisson, Catherine
    Cerruti, Matteo
    Sol, Helene
    Zech, Andreas
    H.E.S.S. Observations of the distant BL Lac PKS 0301-2432012In: HIGH ENERGY GAMMA-RAY ASTRONOMY, American Institute of Physics (AIP), 2012, p. 498-501Conference paper (Refereed)
    Abstract [en]

    PKS 0301-243 is a distant (z=0.266) high-frequency-peaked BL Lac object, detected both at high and very high energies (VHE) with Fermi/LAT and H. E. S. S., and which experienced a flare in May 2010 in the GeV band. H. E. S. S. observations of PKS 0301-243 carried out between September 2009 and December 2011 result in a strong detection of VHE gamma-rays from the source with a significance of 9.8 standard deviations. Multi-wavelength observations from optical to GeV gamma-rays are also presented. The VHE spectrum is used to derive an upper limit on the opacity of the universe to gamma-rays.

  • 324.
    Yadav, K. K.
    et al.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Godambe, S.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    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.
    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.
    Sahayanathan, S.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Observations of TeV γ-rays from Mrk 421 during December 2005 to April 2006 with the TACTIC telescope2007In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 27, no 5, p. 447-454Article in journal (Refereed)
    Abstract [en]

    The TACTIC γ-ray telescope has observed Mrk 421 on 66 clear nights from December 07, 2005 to April 30, 2006, totalling ∼202 h of on-source observations. Here, we report the detection of flaring activity from the source at ⩾1 TeV energy and the time-averaged differential γ-ray spectrum in the energy range 1–11 TeV for the data taken between December 27, 2005 and February 07, 2006 when the source was in a relatively higher state as compared to the rest of the observation period. Analysis of this data spell, comprising ∼97 h reveals the presence of a ∼12.0σ γ-ray signal with daily flux of >1 Crab unit on several days. A pure power law spectrum with exponent −3.11 ± 0.11 as well as a power law spectrum with an exponential cutoff (Γ = −2.51 ± 0.26 and E0 = (4.7 ± 2.1) TeV) are found to provide reasonable fits to the inferred differential spectrum within statistical uncertainties. We believe that the TeV light curve presented here, for nearly 5 months of extensive coverage, as well as the spectral information at γ-ray energies of >5 TeV provide a useful input for other groups working in the field of γ-ray astronomy.

  • 325. Yadav, K. K.
    et al.
    Rannot, R. C.
    Chandra, P.
    Tickoo, A. K.
    Thoudam, Satyendra
    Venugopal, K.
    Bhatt, N.
    Bhattacharyya, S.
    Chanchalani, K.
    Dhar, V. K.
    Godambe, S. V.
    Goyal, H. C.
    Kothari, M.
    Kotwal, S.
    Koul, M. K.
    Koul, R.
    Sahaynathan, S.
    Sharma, M.
    Search for TeV γ-rays from H1426+428 during 2004-2007 with the TACTIC telescope2009In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 36, no 8Article in journal (Refereed)
    Abstract [en]

    The BL Lac object H1426+428 (z ≡ 0.129) is an established source of TeV γ-rays and detections of these photons from this object also have important implications for estimating the extragalactic background light in addition to the understanding of the particle acceleration and γ-ray production mechanisms in the AGN jets. We have observed this source for about 244 h in 2004, 2006 and 2007 with the TACTIC γ-ray telescope located at Mt Abu, India. Detailed analysis of these data do not indicate the presence of any statistically significant TeV γ-ray signal from the source direction. Accordingly, we have placed an upper limit of ≤1.18 × 10−12 photons cm−2 s−1 on the integrated γ-ray flux at 3σ significance level.

  • 326.
    Zacharias, M.
    et al.
    Heidelberg Univ, Germany ; North West Univ, South Africa.
    Bottcher, M.
    North West Univ, South Africa.
    Chakraborty, N.
    Max Planck Inst Kernphys, Germany.
    Cologna, G.
    Heidelberg Univ, Germany.
    Jankowsky, F.
    Heidelberg Univ, Germany.
    Lenain, J. -P
    Mohamed, M.
    Heidelberg Univ, Germany.
    Prokoph, Heike
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Wagner, S.
    Heidelberg Univ, Germany.
    Wierzcholska, A.
    Inst Fizyki Jadrowej PAN, Poland.
    Zaborov, D.
    Ecole Polytech, CNRS, France.
    The Complex VHE And Multiwavelength Flaring Activity Of The FSRQ PKS 1510-089 In May 20152017In: HIGH ENERGY GAMMA-RAY ASTRONOMY / [ed] Aharonian, FA Hofmann, W Rieger, FM, American Institute of Physics (AIP), 2017, article id UNSP 050023Conference paper (Refereed)
    Abstract [en]

    The blazar PKS 1510-089 was the first of the flat spectrum radio quasar type, which had been detected simultaneously by a ground based Cherenkov telescope (H.E.S.S.) and the LAT instrument on board the Fermi satellite. Given the strong broad line region emission defining this blazar class, and the resulting high optical depth for VHE (E > 100 GeV) gamma-rays, it was surprising to detect VHE emission from such an object. In May 2015, PKS 1510-089 exhibited high states throughout the electromagnetic spectrum. Target of Opportunity observations with the H.E.S.S. experiment revealed strong and unprecedented variability of this source. Comparison with the lightcurves obtained with the Fermi-LAT in HE gamma-rays (100 MeV < E < 100 GeV) and ATOM in the optical band shows a complex relationship between these energy bands. This points to a complex structure of the emission region, since the one-zone model has difficulties to reproduce the source behavior even when taking into account absorption by ambient soft photon fields. It will be shown that the presented results have important consequences for the explanation of FSRQ spectra and lightcurves, since the emission region cannot be located deep inside the broad line region as is typically assumed. Additionally, acceleration and cooling processes must be strongly time-dependent in order to account for the observed variability patterns.

  • 327.
    Zucca, P.
    et al.
    ASTRON, Netherlands.
    Morosan, D. E.
    Trinity Coll Dublin, Ireland.
    Rouillard, A. P.
    Inst Rech Astrophys & Planetol, France.
    Fallows, R.
    ASTRON, Netherlands.
    Gallagher, P. T.
    Trinity Coll Dublin, Ireland.
    Magdalenic, J.
    Royal Observ Belgium, Belgium.
    Klein, K-L
    Observ Paris, France.
    Mann, G.
    Leibniz Inst Astrophys Potsdam AIP, Germany.
    Vocks, C.
    Leibniz Inst Astrophys Potsdam AIP, Germany.
    Carley, E. P.
    Trinity Coll Dublin, Ireland.
    Bisi, M. M.
    RAL Space, UK.
    Kontar, E. P.
    Univ Glasgow, UK.
    Rothkaehl, H.
    Polish Acad Sci, Poland.
    Dabrowski, B.
    Univ Warmia & Mazury, Poland.
    Krankowski, A.
    Univ Warmia & Mazury, Poland.
    Anderson, J.
    Helmholtz Zentrum Potsdam, Germany.
    Asgekar, A.
    ASTRON, Netherlands;Shell Technol Ctr, India.
    Bell, M. E.
    Univ Technol Sydney, Australia.
    Bentum, M. J.
    ASTRON, Netherlands;Eindhoven Univ Technol, Netherlands.
    Best, P.
    Univ Edinburgh, UK.
    Blaauw, R.
    ASTRON, Netherlands.
    Breitling, F.
    Leibniz Inst Astrophys Potsdam AIP, Germany.
    Broderick, J. W.
    ASTRON, Netherlands.
    Brouw, W. N.
    ASTRON, Netherlands;Kapteyn Astron Inst, Netherlands.
    Brueggen, M.
    Univ Hamburg, Germany.
    Butcher, H. R.
    Australian Natl Univ, Australia.
    Ciardi, B.
    Max Planck Inst Astrophys, Germany.
    de Geus, E.
    ASTRON, Netherlands;SmarterVision BV, Netherlands.
    Deller, A.
    ASTRON, Netherlands;Swinburne Univ Technol, Australia.
    Duscha, S.
    ASTRON, Netherlands.
    Eisloeffel, J.
    Thuringer Landessternwarte,Germany.
    Garrett, M. A.
    Univ Manchester, UK;Leiden Univ, Netherlands.
    Griessmeier, J. M.
    Univ Orleans, France;CNRS, France.
    Gunst, A. W.
    ASTRON, Netherlands.
    Heald, G.
    ASTRON, Netherlands;CSIRO Astron & Space Sci, Australia.
    Hoeft, M.
    Eindhoven Univ Technol, Netherlands.
    Horandel, J.
    Radboud Univ Nijmegen, Netherlands.
    Iacobelli, M.
    ASTRON, Netherlands.
    Juette, E.
    Ruhr Univ Bochum, Germany.
    Karastergiou, A.
    Univ Oxford, UK.
    van Leeuwen, J.
    Trinity Coll Dublin, Ireland;Univ Amsterdam, Netherlands.
    McKay-Bukowski, D.
    Univ Tromso, Norway;STFC Rutherford Appleton Lab, UK.
    Mulder, H.
    ASTRON, Netherlands.
    Munk, H.
    ASTRON, Netherlands;Radboud Univ Nijmegen, Netherlands.
    Nelles, A.
    Univ Calif Irvine, USA.
    Orru, E.
    ASTRON, Netherlands.
    Paas, H.
    Univ Groningen, Netherlands.
    Pandey, V. N.
    ASTRON, Netherlands;Observ Paris, France.
    Pekal, R.
    Poznan Supercomp & Networking Ctr PCSS, Poland.
    Pizzo, R.
    ASTRON, Netherlands.
    Polatidis, A. G.
    ASTRON, Netherlands.
    Reich, W.
    Max Planck Inst Radioastron, Germany.
    Rowlinson, A.
    ASTRON, Netherlands.
    Schwarz, D. J.
    Univ Bielefeld, Germany.
    Shulevski, A.
    Kapteyn Astron Inst, Netherlands.
    Sluman, J.
    ASTRON, Netherlands.
    Smirnov, O.
    Rhodes Univ, South Africa;SKA South Africa, South Africa.
    Sobey, C.
    Curtin Univ, Australia.
    Soida, M.
    Jagiellonian Univ, Poland.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Toribio, M. C.
    ASTRON, Netherlands;Kapteyn Astron Inst, Netherlands.
    Vermeulen, R.
    ASTRON, Netherlands.
    van Weeren, R. J.
    Kapteyn Astron Inst, Netherlands.
    Wucknitz, O.
    Max Planck Inst Radioastron, Germany.
    Zarka, P.
    Observ Paris, France.
    Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 615, article id A89Article in journal (Refereed)
    Abstract [en]

    Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20-90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. The type II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory (STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with theta(Bn)similar to 70 degrees. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3-1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4-1.6.

4567 301 - 327 of 327
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf