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

We study 59 solar limb flares using the Bragg Crystal Spectrometer (BCS) on Yohkoh and the Burst and Transient Source Experiment (BATSE) to investigat e the relative timings between the Hard X-Ray (HXR) emission and the observ ed non-thermal broadenings of X-ray emission lines (V-nt). We show that the duration of the HXR flux rise to maximum emission affects the relative tim ing of the main V-nt peak with respect to the main HXR peak. In approximate to 20% of the flares studied, secondary peaks in V-nt are observed. These are always associated with a strong HXR pulse and usually occur after the a ssociated HXR pulse. There are also flares that show a relationship between the decay times of V-nt and HXR flux. These results are conducive to a cau sal relationship between the HXR flux and V-nt. We divided the sample of fl ares into two classes, gradual rise and impulsive rise, depending on the sh ape of the HXR lightcurve up to maximum emission. We show that the V-nt beh aviour differs in the two classes. The implications are discussed with a vi ew to understanding the mechanism of V-nt generation.