X‐Ray Spectral Analysis ofYohkohBragg Crystal Spectrometer Data on a 1992 September 6 Flare: The Blueshift Component and Ion Abundances

Abstract

We have studied the time evolution of Bragg crystal spectrometer spectra of He-like Ca XIX and Fe XXV ions observed by the Yohkoh satellite for a solar flare on 1992 September 6 at 05:05 UT (M2.4 class). Electron temperatures are derived through a fit of synthetic spectra to the observed Ca XIX and Fe XXV spectra using new evaluated atomic data. Ion density ratios derived from spectra without assuming ionization equilibrium show a time-dependent, nonequilibrium ionization. The shift from equilibrium values indicates an ionizing plasma. For the first time the emission measures are derived from the spectra without assuming ionization equilibrium and solar abundances. Apparent ion temperatures are derived from the line widths of Ca XIX spectra. In the rising phase a blueshifted component is separated from the main component of the Ca XIX spectra. The time variation of these parameters are compared with hard X-rays, soft X-rays, and radio measurements. In the preheating phase, a moderate increase of the amount of thermal plasma is observed with turbulence indicated by the line width. The time evolution of the blueshifted component coincides with that of a burst in hard X-rays and microwaves which are produced by high-energy, nonthermal electrons.