New features in the radio-emission of very inclined air-showers

SIMON CHICHE; CHAO ZHANG; KUMIKO KOTERA; TIM HUEGE; KRIJN D. DE VRIES; FELIX SCHLÜTER; MATIAS TUEROS

Santiago de Compostela

Workshop; 9th International Workshop on Acoustic and Radio EeV Neutrino Detection Activities; 2022

IGFAE

To probe the sources of ultra-high energy cosmic-rays, the next generation of radio experiments such as GRAND, BEACON and AugerPrime Radio are now focusing on the detection of air-showers arriving with very inclined trajectories. These inclined showers have a large footprint that allows us to instrument large surfaces at low costs, but their radio emission exhibits numerous features that differentiate them from vertical ones. Using Monte-Carlo simulations, we evidence here two major novel features of cosmic-ray inclined showers: a significant drop of more than one order of magnitude in the geomagnetic emission amplitude and a new polarization pattern. We explain the former by a coherence loss in the radio emission of inclined air-showers, while the latter possibly indicates a synchrotron emission becoming relevant at large zenith angles. These two effects depend both on the magnetic field amplitude and are challenging to describe with the existing interpretations of the radio emission but could affect the detection and reconstruction strategies of next generation experiments