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.
Highlights
When a high-energy cosmic particle impinges on the atmosphere of Earth, it creates an extensive air shower (EAS)
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
The comparisons of MGMR3D with CoREAS in the previous section have been done for the Low-Frequency Array (LOFAR) frequency bandwidth of 30–80 MHz
Summary
When a high-energy cosmic particle impinges on the atmosphere of Earth, it creates an extensive air shower (EAS). A simple grid search algorithm suffices to extract the value of Xmax for a fair-weather event, while such a grid search is totally impractical for a thunderstorm event To make such a parameter search more efficient, one needs to be able to deterministically calculate the radio footprint given the structure of the. As an interesting spin-off, the code allows one to investigate which are the essential parameters of the plasma cloud for certain features of the radio pulse footprint In this way—as an example—we noted that the temporal structure of the radio pulse, a strong peak followed by a very shallow undershoot, is strongly determined by the radial dependence of the pancake thickness, see Sec. III. The code, MGMR3D, is available from the authors upon request
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