TEMPORAL FINE-STRUCTURE IN HARD GAMMA-RADIATION IN SOLAR-FLARES

The time evolution of the gamma radiation with an energy above 30 MeV from two powerful solar flares (26 March and 15 June 1991) has been me asured and analyzed. The radiation was detected by the GAMMA-1 orbitin g telescope. The gamma flare of 26 March consisted of a main burst las ting 11 s and several weaker bursts repeating at intervals from 10 s t o several minutes. A fine structure is observed in the bursts. It cons ists of isolated radiation peaks with a time scale of 0.1-0.3 s. It is suggested that the temporal structure of a gamma-ray burst correspond s to discrete particle-acceleration events during the solar flare and, possibly, to a bunching of accelerated beams. The time evolution of t he flare on 15 June, with a duration approximately 2 h, also shows evi dence of discrete radiation bursts.