Some evidences of prolonged particle acceleration in the high‐energy gamma‐ray flare of June 15, 1991

The γ‐ray emission extending to energies greater than 1.5 GeV and lasting at least for two hours was observed from the 3B/X12 two‐ribbon flare of June 15, 1991 with the telescope GAMMA‐1 aboard the GAMMA satellite. A nuclear line emission was also registered in this flare by COMPTEL aboard the CGRO satellite. A comparison of the γ‐ray flux time history with that of microwave emission and analysis of the data on solar cosmic ray fluxes provide an evidence of a long‐term particle acceleration well after the impulsive phase of the flare. It is suggested that such an acceleration may be associated with a long post‐eruptive energy release after a coronal mass ejection (CME).