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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg
The Oriented Scintillation Spectrometer Experiment (OSSE) on board the COMPTON Gamma Ray Observatory observed the 1991 June 4 X12+ solar flare, one of the most intense nuclear gamma-ray line flares observed to date. Using these OSSE observations, we have derived time profiles of the various components of gamma-ray emission and obtained information about the accelerated particle spectra and composition and about the ambient plasma at the flare site. The main results of the analysis are: the nuclear reactions producing the gamma rays continued for more than 3 hours and resulted from ions that were probably accelerated continuously rather than impulsively followed by trapping; (2) the total energy in these accelerated ions exceeded the energy in >0.1 MeV electrons by at least an order of magnitude; (3) the accelerated alpha/proton ratio was greater than 0.1 and probably closer to 0.5; (4) the accelerated heavy ion-to-proton ratio appears to have decreased as the flare progressed (5) the ambient abundance of elements with low First Ionization Potential (FIP) relative to those with high FIP appears to have increased as the flare progressed; (6) the high-energy (>16 MeV) component of the electron spectrum was much more impulsive than the lower-energy \simMeV component; (7) a model-dependent upper limit of 2.3 \times 10^-5 was obtained for the photospheric ^3He/H abundance ratio; and (8) energetic ions may have been present for several hours prior to and following the impulsive phase of the flare.
This work was supported by NASA DPR S-92556-F.
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