Evolution of Flare-accelerated Electrons Quantified by Spatially Resolved Analysis

TL;DR

This study combines microwave imaging spectroscopy and hard X-ray data to analyze the spatial and spectral evolution of nonthermal electrons during a solar flare, revealing distinct behaviors in different electron energy populations.

Contribution

It introduces a joint analysis method of MW and HXR data to spatially resolve electron evolution, highlighting spectral hardening in high-energy electrons during a flare.

Findings

High-energy electrons show significant spectral hardening over time.

Low-energy electrons exhibit less spectral evolution.

Results support a trap-plus-precipitation model with ongoing electron acceleration.

Abstract

Nonthermal electrons accelerated in solar flares produce electromagnetic emission in two distinct, highly complementary domains - hard X-rays (HXRs) and microwaves (MWs). This paper reports MW imaging spectroscopy observations from the Expanded Owens Valley Solar Array of an M1.2 flare that occurred on 2017 September 9, from which we deduce evolving coronal parameter maps. We analyze these data jointly with the complementary Reuven Ramaty High-Energy Solar Spectroscopic Imager HXR data to reveal the spatially-resolved evolution of the nonthermal electrons in the flaring volume. We find that the high-energy portion of the nonthermal electron distribution, responsible for the MW emission, displays a much more prominent evolution (in the form of strong spectral hardening) than the low-energy portion, responsible for the HXR emission. We show that the revealed trends are consistent with a single electron population evolving according to a simplified trap-plus-precipitation model with sustained injection/acceleration of nonthermal electrons, which produces a double-powerlaw with steadily increasing break energy.