Macroscopic Treatment of Radio Emission from Cosmic Ray Air Showers based on Shower Simulations

TL;DR

This paper develops a macroscopic model to calculate the radio emission from cosmic ray air showers, linking the electromagnetic signals to simulated current variations in a realistic magnetic field, highlighting the dominant contributions and signal characteristics.

Contribution

It introduces a macroscopic approach based on shower simulations to analyze radio emissions, emphasizing the roles of current variation, geomagnetic effects, and ion contributions.

Findings

The main pulse is related to current time variation.

Geomagnetic field effects dominate for inclined showers.

The radio signal exhibits a bipolar shape.

Abstract

We present a macroscopic calculation of coherent electro-magnetic radiation from air showers initiated by ultra-high energy cosmic rays, based on currents obtained from Monte Carlo simulations of air showers in a realistic geo-magnetic field. We can clearly relate the time signal to the time dependence of the currents. We find that the the most important contribution to the pulse is related to the time variation of the currents. For showers forming a sufficiently large angle with the magnetic field, the contribution due to the currents induced by the geo-magnetic field is dominant, but neither the charge excess nor the dipole contribution can be neglected. We find a characteristic bipolar signal. In our calculations, we take into account a realistic index of refraction, whose importance depends on the impact parameter and the inclination. Also very important is the role of the positive ions.