EXOSAT observations of bursts from 2S1636-536: Burst morphology

In two observations with the EXOSAT ME a total of 11 bursts were detected; 7 in July and 4 in May 1984. In terms of rise time and peak count rate there are only 2 kinds, those with a sharp rise and peak count rate of 500 cts/sec/detector and those with a slow rise and a peak count rate of 200 cts/sec/detector. The spectral analysis of these bursts shows a similar situation: for the sharp bright bursts the black body radius increases rapidly to > 20 km and the temperature lags. For the slow dim bursts the temperature rises ahead of the black body radius expansion which is small and slow. The time t _1/2 at which half the total burst energy has been released is 3.5 seconds for bright bursts and 8 seconds for dim ones. These gross differences may be related to the predominance of helium or hydrogen in the thermonuclear flash.