RESIK observations of He-like Ar X-ray line emission in solar flares

TL;DR

This study analyzes He-like Argon X-ray lines observed in solar flares by RESIK, examining line ratios, temperature dependence, and elemental abundances, revealing insights into flare plasma conditions and nonthermal effects.

Contribution

First detailed analysis of Ar XVII X-ray lines in solar flares using RESIK data, including temperature diagnostics and abundance measurements.

Findings

G ratio varies with electron temperature and agrees with models

S/Ar abundance ratio matches coronal values

Evidence of nonthermal contributions in some spectra

Abstract

The Ar XVII X-ray line group principally due to transitions 1s2 - 1s2l (l=s, p) near 4 Anstroms was observed in numerous flares by the RESIK bent crystal spectrometer aboard CORONAS-F between 2001 and 2003. The three line features include the Ar XVII w (resonance line), a blend of x and y (intercombination lines), and z (forbidden line), all of which are blended with Ar XVI dielectronic satellites. The ratio G, equal to [I(x+y) + I(z)]/I(w), varies with electron temperature Te mostly because of unresolved dielectronic satellites. With temperatures estimated from GOES X-ray emission, the observed G ratios agree fairly well with those calculated from CHIANTI and other data. With a two-component emission measure, better agreement is achieved. Some S XV and S XVI lines blend with the Ar lines, the effect of which occurs at temperatures greater than 8MK, allowing the S/Ar abundance ratio to be determined. This is found to agree with coronal values. A nonthermal contribution is indicated for some spectra in the repeating-pulse flare of 2003 February 6.