Validation of straight-line signal propagation for radio signal of very inclined cosmic ray air showers

TL;DR

This study assesses the accuracy of straight-line radio signal propagation models for very inclined cosmic ray air showers, finding they are sufficiently precise up to 600 MHz and 88° zenith angles.

Contribution

It improves the electric field calculation in simulations by incorporating tabulated ray tracing data to evaluate straight-line assumptions.

Findings

2% difference in radiation energy

O(0.01°) difference in direction reconstruction

Validates straight-line approximation for frequencies up to 600 MHz and zenith angles up to 88°

Abstract

An ongoing challenge for radio-based detectors of high-energy cosmic particles is the accurate description of radio signal propagation in natural nonuniform media. For radio signals originating from extensive air showers, the current state of the art simulations often implicitly assume straight-line signal propagation. The refraction due to a nonuniform atmosphere is however expected to have an effect on the received signal and associated reconstruction. This effect is currently not completely understood for the most inclined geometries. Here, we present a study regarding the validity of straight-line signal propagation when simulating radio emission associated with very inclined air shower geometries. To this end, the calculation of the electric field based on the end point formalism used in CoREAS was improved by use of tabulated ray tracing data. We find a difference of 2% in radiation energy and a difference of O(0.01{\deg}) on direction reconstruction when working at frequencies below 600 MHz. We thus find that, for frequencies up to 600 MHz and zenith angles up to 88{\deg}, the current straight-line based simulation approaches are accurate.