The shape of the radio wavefront of extensive air showers as measured with LOFAR
Journal
Date Issued
2015
Author(s)
Corstanje, A.
•
Schellart, P.
•
Nelles, A.
•
Buitink, S.
•
Enriquez, J. E.
•
Falcke, H.
•
Frieswijk, W.
•
Hörandel, J. R.
•
Krause, M.
•
Rachen, J. P.
•
Scholten, O.
•
ter Veen, S.
•
Thoudam, S.
•
Trinh, T. N. G.
•
van den Akker, M.
•
Alexov, A.
•
Anderson, J.
•
Avruch, I. M.
•
Bell, M. E.
•
Bentum, M. J.
•
•
Best, P.
•
•
Breitling, F.
•
Broderick, J.
•
Brüggen, M.
•
Butcher, H. R.
•
Ciardi, B.
•
•
de Geus, E.
•
de Vos, M.
•
Duscha, S.
•
Eislöffel, J.
•
Engels, D.
•
Fallows, R. A.
•
Ferrari, C.
•
Garrett, M. A.
•
Grießmeier, J.
•
Gunst, A. W.
•
Hamaker, J. P.
•
Hoeft, M.
•
Horneffer, A.
•
Iacobelli, M.
•
Juette, E.
•
Karastergiou, A.
•
Kohler, J.
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Kondratiev, V. I.
•
Kuniyoshi, M.
•
Kuper, G.
•
Maat, P.
•
Mann, G.
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McFadden, R.
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McKay-Bukowski, D.
•
Mevius, M.
•
Munk, H.
•
Norden, M. J.
•
Orru, E.
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Paas, H.
•
Pandey-Pommier, M.
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Pandey, V. N.
•
Pizzo, R.
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Polatidis, A. G.
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Reich, W.
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Röttgering, H.
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Scaife, A. M. M.
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Schwarz, D.
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Smirnov, O.
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Stewart, A.
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Steinmetz, M.
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Swinbank, J.
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Tagger, M.
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Tang, Y.
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Tasse, C.
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Toribio, C.
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Vermeulen, R.
•
Vocks, C.
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van Weeren, R. J.
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Wijnholds, S. J.
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Wucknitz, O.
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Yatawatta, S.
•
Zarka, P.
Description
Acknowledgments The authors thank Eric Cator for a useful discussion on statistical tests, and thank the anonymous referee for constructive comments. The LOFAR Key Science Project Cosmic Rays very much acknowledges the scientific and technical support from ASTRON. Furthermore, we acknowledge financial support from the Netherlands Research School for Astronomy (NOVA), the Samenwerkingsverband Noord-Nederland (SNN) and the Foundation for Fundamental Research on Matter (FOM) as well as support from the Netherlands Organization for Scientific Research (NWO), VENI grant 639-041-130. We acknowledge funding from an Advanced Grant of the European Research Council under the European Unions Seventh Framework Program (FP/2007-2013)/ ERC Grant Agreement n. 227610. Chiara Ferrari acknowledges financial support by the Agence Nationale de la Recherche through grant ANR-09-JCJC-0001-01. LOFAR, the Low Frequency Array designed and constructed by ASTRON, has facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the International LOFAR Telescope (ILT) foundation under a joint scientific policy.
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.
Volume
61
Start page
22
Issn Identifier
0927-6505
Ads BibCode
2015APh....61...22C
Rights
open.access
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