A Joint Microwave and Hard X-Ray Study Towards Understanding the Transport of Accelerated Electrons during an Eruptive Solar Flare

TL;DR

This study combines microwave and X-ray observations from two perspectives to analyze electron transport in solar flares, revealing differences in electron distributions at coronal and footpoint sources and highlighting the importance of multi-wavelength diagnostics.

Contribution

It provides a detailed comparison of nonthermal electron distributions at coronal and footpoint sources using simultaneous radio and X-ray data, advancing understanding of electron transport during solar flares.

Findings

Footpoint electron flux is an order of magnitude greater than trapped electrons.

X-ray spectral indices are softer than microwave-derived electron spectra.

Differences are due to transport effects and observational sensitivities.

Abstract

The standard flare model, despite its success, is limited in comprehensively explaining the various processes involving nonthermal particles. One such missing ingredient is a detailed understanding of the various processes involved during the transport of accelerated electrons from their site of acceleration to different parts of the flare region. Here we use simultaneous radio and X-ray observations from the Expanded Owens Valley Solar Array (EOVSA) and Spectrometer/Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter (SolO), respectively, from two distinct viewing perspectives to study the electron transport processes. Through detailed spectral modeling of the coronal source using radio data and footpoint sources using X-ray spectra, we compare the nonthermal electron distribution at the coronal and footpoint sources. We find that the flux of nonthermal electrons precipitated at the footpoint is an order of magnitude greater than that trapped in the looptop, consistent with earlier works which primarily used X-ray for their studies. In addition, we find that the electron spectral indices obtained from X-ray footpoints is significantly softer than the spectral hardness of the nonthermal electron distribution in the corona. We interpret these differences based on transport effects and the difference in sensitivity of microwave and X-ray observations to different regimes of electron energies. Such an understanding is crucial for leveraging different diagnostic methods of nonthermal electrons simultaneously to achieve a more comprehensive understanding of the electron acceleration and transport processes of solar flares.