Calculations of low-frequency radio emission by cosmic ray-induced particle showers

TL;DR

This paper develops a comprehensive formula for calculating low-frequency radio emissions from cosmic ray-induced particle showers, extending beyond the far-field approximation, and implements it in a simulation to study low-frequency signals.

Contribution

It introduces a new formula valid for all frequencies to compute electric fields from particle showers and incorporates it into a simulation to analyze low-frequency emissions.

Findings

Derived a frequency-inclusive electric field formula

Implemented the formula in the SELFAS Monte Carlo code

Studied properties of the sudden death pulse (SDP) emission

Abstract

The radio technique for the detection of high energy cosmic rays consists in measuring the electric field created by the particle showers created inside a medium by the primary cosmic ray. The electric field is then used to infer the properties of the primary particle. Nowadays, the radio technique is a standard, well-established technique. While most current experiments measure the field at frequencies above $20$ MHz, several experiments have reported a large emission at low frequencies, below $10$ MHz. The EXTASIS experiment aims at measuring again and understand this low-frequency electric field. Since at low frequencies the standard far-field approximation for the calculation of the electric field does not necessarily hold, in order to comprehend the low-frequency emission we need to go beyond the far-field approximation. We present in this work a formula for the electric field created by a particle track inside a dielectric medium that is valid for all frequencies. We then implement this formula in the SELFAS Monte Carlo code and calculate the low-frequency electric field of EAS. We also introduce the sudden death pulse (SDP), an emission caused by the coherent deceleration of the shower front, and study its properties.