期刊
ASTROPARTICLE PHYSICS
卷 61, 期 -, 页码 22-31出版社
ELSEVIER
DOI: 10.1016/j.astropartphys.2014.06.001
关键词
Cosmic rays; Extensive air showers; Radio emission; Wavefront shape
资金
- Netherlands Research School for Astronomy (NOVA)
- Samenwerkingsverband Noord-Nederland (SNN)
- Foundation for Fundamental Research on Matter (FOM)
- Netherlands Organization for Scientific Research (NWO) [639-041-130]
- Advanced Grant of the European Research Council under the European Union [227610]
- Agence Nationale de la Recherche [ANR-09-JCJC-0001-01]
- STFC [ST/M001423/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/M001423/1] Funding Source: researchfish
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. (C) 2014 Elsevier B.V. All rights reserved.
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