Comparing LOPES measurements of air-shower radio emission with REAS 3.11 and CoREAS simulations

Abstract

Cosmic ray air showers emit radio pulses at MHz frequencies, which can be measured with radio antenna arrays - like LOPES at the Karlsruhe Institute of Technology in Germany. To improve the understanding of the radio emission, we test theoretical descriptions with measured data. The observables used for these tests are the absolute amplitude of the radio signal, and the shape of the radio lateral distribution. We compare lateral distributions of more than 500 LOPES events with two recent and public Monte Carlo simulation codes, REAS 3.11 and CoREAS (v 1.0). The absolute radio amplitudes predicted by REAS 3.11 are in good agreement with the LOPES measurements. The amplitudes predicted by CoREAS are lower by a factor of two, and marginally compatible with the LOPES measurements within the systematic scale uncertainties. In contrast to any previous versions of REAS, REAS 3.11 and CoREAS now reproduce the shape of the measured lateral distributions correctly. This reflects a remarkable progress compared to the situation a few years ago, and it seems that the main processes for the radio emission of air showers are now understood: The emission is mainly due to the geomagnetic deflection of the electrons and positrons in the shower. Less important but not negligible is the Askaryan effect (net charge variation). Moreover, we confirm that the refractive index of the air plays an important role, since it changes the coherence conditions for the emission: Only the new simulations including the refractive index can reproduce rising lateral distributions which we observe in a few LOPES events. Finally, we show that the lateral distribution is sensitive to the energy and the mass of the primary cosmic ray particles.

Attention: results and conclusion partly changed due to updated calibration. See Astroparticle Physics 75 (2016) 72-74; arXiv:1507.07389

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• Design and Performance of an Interferometric Trigger Array for Radio Detection of High-Energy Neutrinos
• A comparison of the cosmic-ray energy scales of Tunka-133 and KASCADE-Grande via their radio extensions Tunka-Rex and LOPES
• The wavefront of the radio signal emitted by cosmic ray air showers
• Improved absolute calibration of LOPES measurements and its impact on the comparison with REAS 3.11 and CoREAS simulations
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• The renaissance of radio detection of cosmic rays
• On the prospects of ultra-high energy cosmic rays detection by high altitude antennas
• Final results of the LOPES radio interferometer for cosmic-ray air showers
• Status of air-shower measurements with sparse radio arrays (ARENA 2016)