Solar Physics Division Meeting 2000, June 19-22
Session 14. Flares and Transients
Oral, Chair: P. L. Bornmann, Thursday, June 22, 2000, 11:00am-12:00noon, 1:30-2:30pm, Forum

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[14.08] COMPTEL Gamma-Ray Observations of the C4 Solar Flare on 20 January 2000

J.M. Ryan, M. Arndt, J.A. Lockwood, M.L. McConnell, R. Miller, C.A. Young (UNH), R. Diehl, G. Rank, V. Schoenfelder (MPE), K. Bennett, C. Winkler (ESTEC), H. Debrunner (U Bern)

In response to a BACODINE cosmic gamma-ray burst alert, COMPTEL on the Compton Gamma Ray Observatory recorded gamma rays above 1 MeV from the C4 flare at 0221 UT 20 January 2000. Although the candidate burst was, in fact, the solar flare, the COMPTEL analysis system produced an image of the transient centered within statistics on the Sun. A preliminary combined BATSE/COMPTEL spectrum shows a bremsstrahlung continuum with a power law index of approximately -3.1, on top of which rides a nuclear line component that falls off at the expected energy of 8 MeV. Although subject to the uncertain extrapolation of the bremsstrahlung continuum, the ratio of the nuclear component to the bremsstrahlung component tends to be higher than the same ratio for the distribution of flares measured with SMM. Only one C flare exhibited gamma-ray emission above 1 MeV in the SMM atlas. However, the fact that a "normal" solar flare gamma-ray spectrum can originate from a C4 flare, throws into question the concept of a minimum flare size for proton or relativistic electron acceleration.

This work was in part supported by NASA NAS5-26645, the German government 50 Q 9096 8 and the Swiss National Science Foundation 20-50697.97.

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