EUV Spectra of Solar Flares from the EUV Spectroheliograph SPIRIT aboard CORONAS-F satellite

TL;DR

This paper presents the first detailed EUV spectra of large solar flares obtained with high spectral resolution, analyzing line identifications, plasma temperatures, and densities to improve understanding of flare plasma conditions.

Contribution

It provides the first high-resolution EUV spectra of large solar flares and performs comprehensive spectral line identification and plasma diagnostics using synthetic spectra.

Findings

Over 50 spectral lines identified, mainly from Fe, Ni, Ca, Mg, Si.

DEM peaks at around 10 MK, indicating plasma temperature distribution.

Average plasma density of 6.5 x 10^9 cm^-3 derived from line analysis.

Abstract

We present detailed EUV spectra of 4 large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176-207 \AA\ and 280-330 \AA. These spectra were obtained {by the slitless} spectroheliograph SPIRIT aboard the CORONAS-F satellite. To our knowledge these are the first detailed EUV spectra of large flares obtained with spectral resolution of $\sim 0.1$ \AA. We performed a comprehensive analysis of the obtained spectra and provide identification of the observed spectral lines. The identification was performed based {on the calculation} of synthetic spectra (CHIANTI database was used), with simultaneous {calculations of DEM} and density of the emitting plasma. More than 50 intense lines are present in the spectra that correspond to a temperature range of $T=0.5-16$ MK; most of the lines belong to Fe, Ni, Ca, Mg, Si ions. In all the considered flares intense hot lines from Ca XVII, Ca XVIII, Fe XX, Fe XXII, and Fe XXIV are observed. The calculated DEMs have a peak at $T \sim 10$ MK. The densities were determined using Fe XI - Fe XIII lines and averaged $6.5 \times 10^9$ cm$^{-3}$. We also discuss the identification, accuracy and major discrepancies of the spectral line intensity prediction.