Comparative Analysis of Non-thermal Emissions and Study of Electron Transport in a Solar Flare

TL;DR

This study analyzes non-thermal emissions in a solar flare using RHESSI and Nobeyama data, revealing electron transport characteristics and pitch-angle distributions through modeling and comparison with observations.

Contribution

It introduces a detailed electron transport model ({ exttt{TPP}}) to interpret non-thermal emissions and infers the pitch-angle distribution of electrons in a solar flare.

Findings

Microwave peaks lag behind HXR peaks.

Electrons likely have a perpendicular pitch-angle distribution.

Model explains spectral variations qualitatively.

Abstract

We study the non-thermal emissions in a solar flare occurring on 2003 May 29 by using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This flare shows several typical behaviors of the HXR and microwave emissions: time delay of microwave peaks relative to HXR peaks, loop-top microwave and footpoint HXR sources, and a harder electron energy distribution inferred from the microwave spectrum than from the HXR spectrum. In addition, we found that the time profile of the spectral index of the higher-energy ($\gsim 100$ keV) HXRs is similar to that of the microwaves, and is delayed from that of the lower-energy ($\lsim 100$ keV) HXRs. We interpret these observations in terms of an electron transport model called {\TPP}. We numerically solved the spatially-homogeneous {\FP} equation to determine electron evolution in energy and pitch-angle space. By comparing the behaviors of the HXR and microwave emissions predicted by the model with the observations, we discuss the pitch-angle distribution of the electrons injected into the flare site. We found that the observed spectral variations can qualitatively be explained if the injected electrons have a pitch-angle distribution concentrated perpendicular to the magnetic field lines rather than isotropic distribution.