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Session 26 - Solar Flares II.
Oral session, Monday, June 10
Wisconsin Center,
The June 1991 solar flares were among the most intense flares ever observed. During the 11 June flare the GOES soft X-ray detectors were saturated for more than 20 minutes with emission lasting for more than 4 hours. Remarkably, this flare was observed by \itCGRO/EGRET (Kanbach et al. 1992) to produce >50 MeV emission for more than 8 hours after the peak, raising questions about whether this emission was from interactions of continuously-accelerated particles or prolonged release of trapped particles (Ramaty and Mandzhavidze, 1993). A consequence of trapping is a hardening of the interacting-particle spectrum with time as higher-energy particles are more quickly removed from the population. The detailed spectral analysis possible with \itCGRO/OSSE can directly measure the particle spectum by comparing the relative fluxes of the 2.223 MeV neutron-capture line and nuclear-de-excitation lines. The 4 June flare, which was even more intense than the 11 June flare, was not observable by EGRET but was accessible to OSSE and observations were made during the peak and for several orbits during the decay. Previously, we have reported preliminary results of the analysis of the first two orbits suggesting the possibility of a spectral softening. Here we report on a more extended search for emission from the 4 June 1991 solar flare using the OSSE data. The neutron-capture line and nuclear-de-excitation line fluxes will be derived using two methods for determining the background. The implications of the results on particle acceleration and trapping will be discussed.
