Coronal Electron Distribution in Solar Flares: Drift-Kinetic Model

TL;DR

This study models how pitch-angle scattering affects the height distribution of electrons in solar flares, explaining observed X-ray source positions and highlighting the importance of scattering in electron transport.

Contribution

It introduces a drift-kinetic model that accounts for energy-dependent pitch-angle scattering to explain coronal electron height distributions in solar flares.

Findings

Energy-dependent electron heights are explained by pitch-angle scattering effects.

Intermediate energy electrons are inhibited from following shrinking magnetic loops.

Qualitative agreement with observed X-ray source positions is achieved.

Abstract

Using a model of particle acceleration and transport in solar flares, we investigate the height distribution of coronal electrons by focusing on the energy-dependent pitch-angle scattering. When pitch-angle scattering is not included, the peak heights of loop-top electrons are constant, regardless of their energy, owing to the continuous acceleration and compression of the electrons via shrinkage of magnetic loops. On the other hand, under pitch-angle scattering, the electron heights are energy dependent; intermediate energy electrons are at a higher altitude, whereas lower and higher energy electrons are at lower altitudes. This implies that the intermediate energy electrons are inhibited to follow the shrinking field lines to lower altitudes because pitch-angle scattering causes efficient precipitation of these electrons into the footpoint and their subsequent loss from the loop. This result is qualitatively consistent with the position of the above-the-loop-top hard X-ray (HXR) source that is located above coronal HXR loops emitted by lower energy electrons and microwaves emitted by higher energy electrons. Quantitative agreement with observations might be achieved by considering primary acceleration before the onset of loop shrinkage and additional pitch-angle scattering via wave-particle interactions.