Observations of Thermal Flare Plasma with the EUV Variability Experiment

TL;DR

This study uses the EUV Variability Experiment to analyze the thermal structure of solar flare plasma, revealing that the plasma's temperature distribution is broad and that the isothermal assumption is often inaccurate.

Contribution

The paper introduces a method to compute the differential emission measure distribution from EVE observations and demonstrates its application to multiple solar flare events.

Findings

Differential emission measure distribution is broad during all flare phases.

The isothermal approximation poorly represents the thermal structure of flares.

EVE spectra provide detailed insights into flare plasma temperatures.

Abstract

One of the defining characteristics of a solar flare is the impulsive formation of very high temperature plasma. The properties of the thermal emission are not well understood, however, and the analysis of solar flare observations is often predicated on the assumption that the flare plasma is isothermal. The EUV Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO) provides spectrally resolved observations of emission lines that span a wide range of temperatures (e.g., Fe XV-Fe XXIV) and allow for thermal flare plasma to be studied in detail. In this paper we describe a method for computing the differential emission measure distribution in a flare using EVE observations and apply it to several representative events. We find that in all phases of the flare the differential emission measure distribution is broad. Comparisons of EVE spectra with calculations based on parameters derived from the GOES soft X-ray fluxes indicate that the isothermal approximation is generally a poor representation of the thermal structure of a flare.