Numerical Study of a Propagating Non-Thermal Microwave Feature in a Solar Flare Loop

TL;DR

This study uses analytical and numerical methods to understand the apparent propagation of non-thermal microwave sources in a solar flare loop, revealing it results from ensemble electron behavior rather than individual electron motion.

Contribution

It demonstrates that the propagating microwave feature arises from a distribution of electrons with varying pitch angles, not from electrons moving with a specific initial pitch angle.

Findings

The propagating feature is due to ensemble electron behavior.

Electrons are isotropically accelerated before injection.

The model matches observed microwave propagation patterns.

Abstract

We analytically and numerically study the motion of electrons along a magnetic loop, to compare with the observation of the propagating feature of the non-thermal microwave source in the 1999 August 28 solar flare reported by Yokoyama et al. (2002). We model the electron motion with the Fokker-Planck equation and calculate the spatial distribution of the gyrosynchrotron radiation. We find that the microwave propagating feature does not correspond to the motion of electrons with a specific initial pitch angle. This apparent propagating feature is a consequence of the motion of an ensemble of electrons with different initial pitch angles, which have different time and position to produce strong radiation in the loop. We conclude that the non-thermal electrons in the 1999 August 28 flare were isotropically accelerated and then are injected into the loop.