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

Abstract

Nonthermal particle acceleration in the solar corona is evident from both remote hard X-ray 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 independently varying the turbulent acceleration timescale τ _acc , acceleration profile standard deviation σ , and acceleration region length L result in an 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 ~0.5. It was also found that the in situ spectral index δ derived from the peak electron flux produces a spectral index ~1.6 harder than that from a full-flare X-ray photon flux (of spectral index γ ) simulated with the same intermediate parameters. Previous studies have indicated an approximate δ ≈ γ relationship for selected flares with measured in situ electron and X-ray photon observations, suggesting that an extended source region with nonuniform plasma and/or acceleration properties may be necessary to reproduce this relationship.

Keywords

• Active solar corona
• Heliosphere
• Solar flares
• Solar energetic particles