Exploring the Origin of Solar Energetic Electrons II: Investigating Turbulent Coronal Acceleration

TL;DR

This study investigates how turbulent acceleration in the solar corona influences the spectral properties of energetic electrons, aiming to understand their origin and the connection between remote and in-situ observations.

Contribution

It performs a parameter study on turbulent acceleration properties and their effects on electron spectra, providing new insights into the acceleration region characteristics and spectral index variations.

Findings

Short timescale turbulence steepens electron spectra.

In-situ spectral index is about 1.6 harder than X-ray derived index.

Extended, non-uniform acceleration regions may explain spectral relationships.

Abstract

Non-thermal particle acceleration in the solar corona is evident from both remote hard X-ray (HXR) sources in the chromosphere and direct in-situ detection in the heliosphere. Correlation of spectral indices between remote and in-situ energy spectra presents the possibility of a common source acceleration region within the corona, however the properties and location of this region are not well constrained. To investigate this we perform a parameter study for both the properties of the ambient plasma of a simulated acceleration region and the turbulent acceleration profile acting on an initially isotropic thermal electron population. We find that the independently varying the turbulent acceleration timescale $\tau_{acc}$, acceleration profile standard deviation ${\sigma}$ and acceleration region length L result in in-situ spectral index variation of between 0.5 and 2.0 at 1.0 AU for < 100 keV electrons. Short timescale turbulent scattering in the flaring corona steepens the spectra by $\sim$ 0.5. It was also found that the in-situ spectral index $\delta$ derived from the peak electron flux produces a spectral index $\sim$ 1.6 harder than that from a full-flare X-ray photon flux (of spectral index $\gamma$) simulated with the same intermediate parameters. Previous studies have indicated an approximate $\delta \approx \gamma$ relationship for selected flares with measured in-situ electron and X-ray photon observations, suggesting that an extended source region with non-uniform plasma and/or acceleration properties may be necessary to reproduce this relationship.