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Astron. Astrophys. 340, 257-264 (1998)

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Deduced spectrum of interacting protons accelerated after the impulsive phase of the 15 June 1991 solar flare

L. Kocharov 1, H. Debrunner 2, G. Kovaltsov, * 1, J. Lockwood 3, M. McConnell 3, P. Nieminen 2, G. Rank 4, J. Ryan 3 and V. Schönfelder 4

1 Space Research Laboratory, University of Turku, Turku FIN-20014, Finland
2 Physical Institute, University of Bern, CH-3012 Bern, Switzerland
3 Space Science Center, University of New Hampshire, Durham NH 03824, USA
4 Max Planck Institute for Extraterrestrial Physics, P.O. Box 1603, D-85740 Garching, Germany

Received 11 March 1998 / Accepted 15 September 1998


In June 1991 the Sun produced a famous series of six powerful flares. For the solar eruption on 15 June 1991 there exists a rich set of measurements, including in particular [FORMULA]-ray and neutron observations of the COMPTEL instrument on board the COMPTON Gamma Ray Observatory (CGRO) satellite. The [FORMULA]-ray and neutron emissions indicate prolonged acceleration of protons well after the impulsive phase of the flare. Some accelerated particles interact with solar matter and produce [FORMULA]-rays and neutrons at the Sun, others escape into the interplanetary medium. Here we present the deduced energy spectrum of the interacting protons for a nearly one hour period in the gradual phase of the flare. From the low-energy [FORMULA]-ray and neutron results of COMPTEL we determine the energy spectrum of the interacting protons in the 10-200 MeV range. We find that the COMPTEL data are consistent with a proton power law spectrum with index [FORMULA]. To simultaneously fit the high-energy [FORMULA]-ray measurements on board the GAMMA-1 satellite, the spectrum must steepen at a few hundred MeV and then become harder again to produce a detectable amount of GeV photons. Although the degree of steepening is composition dependent, the deduced spectrum of interacting protons is qualitatively invariant in the entire parameter region [FORMULA].

Key words: Sun: activity – Sun: flares – Sun: particle emission – Sun: X-rays, gamma rays

* Present address: A.F. Ioffe Physical-Technical Institute, St. Petersburg 194021, Russia

© European Southern Observatory (ESO) 1998

Online publication: November 3, 1998