The convergence of EAS radio emission models and a detailed comparison of REAS3 and MGMR simulations

TL;DR

This paper compares two radio emission models for cosmic ray air showers, REAS3 and MGMR, demonstrating that including the missing charge variation contribution reconciles previous discrepancies and leads to close agreement between models.

Contribution

The study shows that accounting for the charge variation contribution in REAS3 aligns it with MGMR, marking a significant step towards unified radio emission modeling.

Findings

REAS3 and MGMR models agree closely when charge variation is included.

Discrepancies are mainly due to differences in underlying air shower models.

This is the first demonstration of such concordance between independent radio emission models.

Abstract

Over the previous decade, many approaches for the modelling of radio emission from cosmic ray air showers have been developed. However, there remained significant deviations between the models, reaching from important qualitative differences such as unipolar versus bipolar pulses to large variations in the predicted absolute amplitudes of up to factors of 20. Only recently, it has been realized that in the many models predicting unipolar pulses, a radio emission contribution due to the time-variation of the number of charged particles or, equivalently, the acceleration of the particles at the beginning and the end of their trajectories, had not been taken into account. We discuss here the nature of the underlying problem and demonstrate that by including the missing contribution in REAS3, the discrepancies are reconciled. Furthermore, we show a direct comparison of REAS3 and MGMR simulations for a set of prototype showers. The results of these two completely independent and very different modelling approaches show a good level of agreement except for regions of parameter space where differences in the underlying air shower model become important. This is the first time that two radio emission models show such close concordance, illustrating that the modelling of radio emission from extensive air showers has indeed made a true breakthrough.