Extended gamma-ray emission of the solar flares in June 1991

During the solar flares on 9, 11, and 15 June 1991 the COMPTEL instrument m easured extended gamma -radiation in the 2.223 MeV neutron-capture line, in prompt nuclear deexcitation lines and in pion-decay radiation for several hours after the flares. The long-term time profiles can be described by a d ouble exponential decay with decay constants on the order of 10 min for the fast and several 100 min for the slow components. We studied the 11 June 1 991 are in more detail and found that during the extended phase the acceler ated proton and ion spectrum is harder, the e/p ratio is lower, and the emi ssion profile is smoother, compared to those of the impulsive phase. Pion-d ecay radiation was not detected before the onset of the extended emission p hase. When comparing the three flares to one another, we found a striking s imilarity in the time profiles of the nuclear line and the neutron capture line emission. However, the pion-decay radiation varied in intensity signif icantly from are to are. The impulsive-phase emissions of the flares show n o such similarity. Our measurements indicate that the processes taking plac e during the extended phase differ from those during the impulsive phase, o r in other gamma -ray line flares. Based on these results long-term trappin g of energetic particles from the impulsive phase seems unlikely, as oppose d to continuous particle acceleration.