A New Methodology for Inferring the Plasma Conditions in Solar Flare Energetic Electron Source Regions from In Situ Electron Energy Spectra

The conditions within solar flares that lead to efficient electron acceleration are not well constrained. It is not clear whether the populations accelerated out into the heliosphere and inward into the chromosphere originate in the same regions. By analyzing the energy distributions of heliospheric populations, modeling suggests that it should be possible to see evidence of their originating region(s), including the presence of hot, dense flare plasma. By creating and utilizing a novel in situ spectral analysis package called In situ Spectral Executive (INSPEX), we have performed this analysis for flare electrons observed in situ on 2021 October 9, constructing both peak flux and fluence spectra from combined Solar Orbiter in situ electron measurements. We compare how differing methodologies for combining the datasets influence the spectral shapes and the retrieved parameters over an energy range of 0.5–80 keV. We fit different functions to the multicomponent form of the energy spectra, testing combinations of thermal and/or power-law components and comparing the fit statistics. We find that the spectra can be fitted with two distinct thermal curves at energies below 20 keV, corresponding to typical corona/active region and flaring material temperatures, varying between 1.4−4.1 and 12.5−23.1 MK depending on the rebinning window and peak flux extraction method. This study showcases how INSPEX can provide a novel and user-friendly methodology for studying electron spectra with different instrumentation, allowing investigation of multiple spectral types and signatures of acceleration and transport. This first application provides a benchmark case for the analysis of similar flares.