The shape of the radio wavefront of extensive air showers as measured with LOFAR |
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| Affiliation: | 1. Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands;2. Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands;3. Nikhef, Science Park Amsterdam, 1098 XG Amsterdam, The Netherlands;4. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany;5. University of Groningen, P.O. Box 72, 9700 AB Groningen, The Netherlands;6. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA;7. Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany;8. SRON Netherlands Insitute for Space Research, P.O. Box 800, 9700 AV Groningen, The Netherlands;9. Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands;10. ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), Sydney Institute of Astronomy, University of Sydney, Australia;11. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA;12. Institute for Astronomy, University of Edinburgh, Royal Observatory of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK;13. University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany;14. School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK;15. Research School of Astronomy and Astrophysics, Australian National University, Mt Stromlo Obs., via Cotter Road, Weston, A.C.T. 2611, Australia;p. Max Planck Institute for Astrophysics, Karl Schwarzschild Str. 1, 85741 Garching, Germany;q. SmarterVision BV, Oostersingel 5, 9401 JX Assen, The Netherlands;r. Thüringer Landessternwarte, Sternwarte 5, D-07778 Tautenburg, Germany;s. Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany;t. Laboratoire Lagrange, UMR7293, Universitè de Nice Sophia-Antipolis, CNRS, Observatoire de la Cóte d’Azur, 06300 Nice, France;u. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands;v. LPC2E, Universite d’Orleans/CNRS, France;w. Station de Radioastronomie de Nancay, Observatoire de Paris, CNRS/INSU, USR 704, Univ. Orleans, OSUC, route de Souesmes, 18330 Nancy, France;x. Astronomisches Institut der Ruhr-Universität Bochum, Universitaetsstrasse150, 44780 Bochum, Germany;y. Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK;z. Astro Space Center of the Lebedev Physical Institute, Profsoyuznaya str. 84/32, Moscow 117997, Russia;11. Sodankylä Geophysical Observatory, University of Oulu, Tähteläntie 62, 99600 Sodankylä, Finland;12. STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK;13. Center for Information Technology (CIT), University of Groningen, The Netherlands;14. Centre de Recherche Astrophysique de Lyon, Observatoire de Lyon, 9 av Charles André, 69561 Saint Genis Laval Cedex, France;15. Fakultät fr Physik, Universität Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany;16. Department of Physics and Elelctronics, Rhodes University, P.O. Box 94, Grahamstown 6140, South Africa;17. SKA South Africa, 3rd Floor, The Park, Park Road, Pinelands 7405, South Africa;18. Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands;19. LESIA, UMR CNRS 8109, Observatoire de Paris, 92195 Meudon, France;1. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008;2. Key Laboratory of Dark Matter and Space Astronomy, Chinese Academy of Sciences, Nanjing 210008;3. University of Chinese Academy of Sciences, Beijing 100049;1. Departamento de Física, Universidade Estadual da Paraíba, 58429-500 Campina Grande, PB, Brazil;2. Departamento de Física, Universidade Federal da Paraíba, João Pessoa, PB, Brazil;3. Departamento de Astronomia, Observatório Nacional, 20921-400 Rio de Janeiro, RJ, Brazil;1. Lehrstuhl für Astronomie, Universität Würzburg, Emil-Fischer-Straße 31, D-97074 Würzburg, Germany;2. Centre for Space Research, North-West University, 2520 Potchefstroom, South Africa |
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| Abstract: | Extensive air showers, induced by high energy cosmic rays impinging on the Earth’s atmosphere, produce radio emission that is measured with the LOFAR radio telescope. As the emission comes from a finite distance of a few kilometers, the incident wavefront is non-planar. A spherical, conical or hyperbolic shape of the wavefront has been proposed, but measurements of individual air showers have been inconclusive so far. For a selected high-quality sample of 161 measured extensive air showers, we have reconstructed the wavefront by measuring pulse arrival times to sub-nanosecond precision in 200 to 350 individual antennas. For each measured air shower, we have fitted a conical, spherical, and hyperboloid shape to the arrival times. The fit quality and a likelihood analysis show that a hyperboloid is the best parameterization. Using a non-planar wavefront shape gives an improved angular resolution, when reconstructing the shower arrival direction. Furthermore, a dependence of the wavefront shape on the shower geometry can be seen. This suggests that it will be possible to use a wavefront shape analysis to get an additional handle on the atmospheric depth of the shower maximum, which is sensitive to the mass of the primary particle. |
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| Keywords: | Cosmic rays Extensive air showers Radio emission Wavefront shape |
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