Analytic calculation of radio emission from parameterized extensive air showers, a tool to extract shower parameters

TL;DR

This paper introduces a semi-analytical code to calculate radio footprints of extensive air showers, enabling extraction of shower parameters and atmospheric electric field effects from observed radio data.

Contribution

It presents a new semi-analytical method and parametrization for modeling radio footprints, facilitating inverse problem solving to determine shower structure from radio observations.

Findings

The code accurately reproduces CoREAS simulation footprints.

A simple parametrization captures key features of plasma cloud structure.

The method enables extraction of primary cosmic-ray and atmospheric parameters.

Abstract

The radio intensity and polarization footprint of a cosmic-ray induced extensive air shower is determined by the time-dependent structure of the current distribution residing in the plasma cloud at the shower front. In turn, the time dependence of the integrated charge-current distribution in the plasma cloud, the longitudinal shower structure, is determined by interesting physics which one would like to extract such as the location and multiplicity of the primary cosmic-ray collision or the values of electric fields in the atmosphere during thunderstorms. To extract the structure of a shower from its footprint requires solving a complicated inverse problem. For this purpose we have developed a code that semi-analytically calculates the radio footprint of an extensive air shower given an arbitrary longitudinal structure. This code can be used in a optimization procedure to extract the optimal longitudinal shower structure given a radio footprint. On the basis of air-shower universality we propose a simple parametrization of the structure of the plasma cloud. This parametrization is based on the results of Monte-Carlo shower simulations. Deriving the parametrization also teaches which aspects of the plasma cloud are important for understanding the features seen in the radio-emission footprint. The calculated radio footprints are compared with microscopic CoREAS simulations.