Spectroscopic diagnostics of the non-Maxwellian $\kappa$-distributions using SDO/EVE observations of the 2012 March 7 X-class flare

TL;DR

This study investigates non-Maxwellian kappa-distributions in solar flare plasma using SDO/EVE spectroscopic data, revealing significant deviations during flare phases and emphasizing the importance of accounting for these effects in plasma diagnostics.

Contribution

It introduces a method to analyze non-Maxwellian distributions in solar flares using EVE data and the KAPPA database, highlighting the impact on temperature diagnostics and plasma characterization.

Findings

Strong departures from Maxwellian distributions during flare impulsive phases

Temperatures from line ratios are highly dependent on kappa values

Electron density remains nearly constant regardless of kappa

Abstract

Spectroscopic observations made by the Extreme Ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) during the 2012 March 7 X5.4-class flare (SOL2012-03-07T00:07) are analyzed for signatures of the non-Maxwellian kappa-distributions. Observed spectra were averaged over 1 minute to increase photon statistics in weaker lines and the pre-flare spectrum was subtracted. Synthetic line intensities for the kappa-distributions are calculated using the KAPPA database. We find strong departures (kappa < 2) during the early and impulsive phases of the flare, with subsequent thermalization of the flare plasma during the gradual phase. If the temperatures are diagnosed from a single line ratio, the results are strongly dependent on the value of kappa. For kappa=2, we find temperatures about a factor of two higher than the commonly used Maxwellian ones. The non-Maxwellian effects could also cause the temperatures diagnosed from line ratios and from the ratio of GOES X-ray channels to be different. Multithermal analysis reveals the plasma to be strongly multithermal at all times with flat DEMs. For lower kappa, the DEM_kappa are shifted towards higher temperatures. The only parameter that is nearly independent of kappa is electron density, where we find log(N_e) $\approx$ 11.5 almost independently of time. We conclude that the non-Maxwellian effects are important and should be taken into account when analyzing solar flare observations, including spectroscopic and imaging ones.