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Session 18 - The Sun.
Display session, Monday, January 13
In June 1991 the Sun produced a series of six X-class flares. For the flare event on 15 June 1991 there exists a rich set of observations, including optical (H_\alpha from Big Bear Observatory and Warsaw Observatory), radio and microwave emission from various stations, soft and hard X-rays (GOES, BATSE/CGRO) and gamma-rays (COMPTEL/CGRO and GAMMA-1). Also particle measurements of neutrons (COMPTEL) and interplanatary protons (neutron monitor network) have been obtained.
We review these observations and we are able to obtain a composite photon spectrum spanning the energy range from about 25 keV to 4 GeV. As different features in the gamma-ray spectrum are sensitive to different energies of the accelerated proton spectrum, we can probe this proton spectrum from about 10 MeV to a few hundred MeV, showing that the measurements are consistent with a E^-3.5 spectrum.
Extended emission in gamma-rays can be measured for several hours after the impulsive phase by both COMPTEL (nuclear de-excitation lines and neutron capture line at 2.2 MeV) and GAMMA-1 (>50 MeV gamma-rays from pion decay). Within the statistical uncertainlies, both instruments measure the same time behaviour, which can be described by a double exponential decay. This similarity of different energy regimes indicates that continued acceleration of particles dominates over particle trapping during the extended phase.
Program listing for Monday