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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.66] Extended Gamma-Ray Emission of the Solar Flares in June 1991

G. Rank, J. Ryan, M. McConnell, J. Lockwood (Univ. New Hampshire), V. Schöenfelder (MPE, Garching, Germany), H. Debrunner (Univ. Berne, Switzerland)

In June 1991, a series of six X-class solar flares took place in the active region 6659. For the flares on 11 and 15 June 1991, extended gamma-ray emission on time scales of hours has been recorded by COMPTEL, EGRET and GAMMA-1. COMPTEL measures a two-fold exponential decay in the neutron capture line for both flares, with time constants on the order of 10 min for the fast and 200 min for the slow component. Within the statistical uncertainty both flares show the same long-term behaviour. From the study of the neutron capture line, prompt nuclear lines and the gamma-ray continuum above 50 MeV it was found, that the measured decay times are independent of the energy of the accelerated protons. This favours the continuous acceleration of particles over long-term trapping as the explanation of the extended emission.

Here we present updated results for the flares on 11 and 15 June 1991. We also have analyzied COMPTEL telescope data from the flare on 9 June 1991 and present these new results. Our measurements clearly show an extended gamma-ray signal also for this flare.

The long-term behaviour measured in gamma-rays is very similar for all three flares on 9, 11 and 15 June 1991. Our data seem to indicate that the large-scale magnetic structure of this active region remains quite stable during this active period and supports the same kind of long-term acceleration for each flare.

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