Multi-thermal representation of the kappa-distribution of solar flare electrons and application to simultaneous X-ray and EUV observations

TL;DR

This paper introduces a novel method to determine the spectrum of flare-accelerated electrons using a kappa-distribution model fitted to both X-ray and EUV data, improving accuracy in estimating flare energy.

Contribution

It presents the kappa-distribution as a differential emission measure for simultaneous fitting to RHESSI and SDO/AIA data, enabling more precise electron spectrum and energy estimates in solar flares.

Findings

Total energy estimates are more accurate when combining RHESSI and AIA data.

Fitting reduces electron number density by a factor of ~30 and total energy by a factor of ~5.

Electron spectrum shows a low-temperature component and a hot kappa-like component.

Abstract

Acceleration of particles and plasma heating is one of the fundamental problems in solar flare physics. An accurate determination of the spectrum of flare energized electrons over a broad energy range is crucial for our understanding of aspects such as the acceleration mechanism and the total flare energy. Recent years have seen a growing interest in the kappa-distribution as representation of the total spectrum of flare accelerated electrons. In this work we present the kappa-distribution as a differential emission measure. This allows for inferring the electron distribution from X-ray observations and EUV observations by simultaneously fitting the proposed function to RHESSI and SDO/AIA data. This yields the spatially integrated electron spectra of a coronal source between less than 0.1 keV up to several tens of keV. The method is applied to a single-loop GOES C4.1 flare. The results show that the total energy can only be determined accurately by combining RHESSI and AIA observations. Simultaneously fitting the proposed representation of the kappa-distribution reduces the electron number density in the analyzed flare by a factor of ~30 and the total flare energy by a factor of ~5 compared with the commonly used fitting of RHESSI spectra. The spatially integrated electron spectrum of the investigated flare between 0.043 keV and 24 keV is consistent with the combination of a low-temperature (~2 MK) component and a hot (~11 MK) kappa-like component with spectral index 4, reminiscent of solar wind distributions.