The timing of non-thermal soft X-ray emission line broadenings in solar flares

Abstract

We study 59 solar limb flares using the Bragg Crystal Spectrometer (BCS) on Yohkoh and the Burst and Transient Source Experiment (BATSE) to investigate the relative timings between the Hard X-Ray (HXR) emission and the observed non-thermal broadenings of X-ray emission lines (Vnt). We show that the duration of the HXR flux rise to maximum emission aects the relative timing of the main Vnt peak with respect to the main HXR peak. In20% of the flares studied, secondary peaks in Vnt are observed. These are always associated with a strong HXR pulse and usually occur after the associated HXR pulse. There are also flares that show a relationship between the decay times of Vnt and HXR flux. These results are conducive to a causal relationship between the HXR flux and Vnt. We divided the sample of flares into two classes, gradual rise and impulsive rise, depending on the shape of the HXR lightcurve up to maximum emission. We show that the Vnt behaviour diers in the two classes. The implications are discussed with a view to understanding the mechanism of Vnt generation.