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Session 18 - The Sun.
Display session, Monday, January 13
Metropolitan Ballroom,

[18.07] The Solar Flare Event on 15 June 1991

G. Rank, J. Lockwood, M. McConnell, J. Ryan (Univ. of New Hampshire), V. Schönfelder (MPI f. Extraterrestrial Physics, Garching, Germany), K. Bennett (Astroph. Div., ESTEC, Noordwijk, The Netherlands), H. Debrunner, P. Nieminen (Physics Institute, Univ. of Berne, Berne, Switzerland), L. Kocharov, G. Kovaltsov (Univ. of Turku, Turku, Finland)

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.

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