Gamma Ray Observations of the June 1991 Solar Flares

Session 4 - The Sun.
Display session, Monday, June 09
South Main Hall,

[4.03] Gamma Ray Observations of the June 1991 Solar Flares

D. Bertsch, R. Hartman, S. Hunter, D. Thompson (NASA/GSFC), B. Dingus (Utah), J. Esposito, P. Sreekumar (USRA/GSFC), R. Mukherjee (USRA/McGill), C. von Montigny (Heidelberg), Y. Lin, P. Michelson, P. Nolan (Stanford), G. Kanbach, H. Mayerhasselwander (MPE), D. Kniffen (Hampden-Sydney), E. Schneid (Northrop Grumman)

The EGRET instrument on the Compton Gamma Ray Observatory observed four of the X-class solar flares that occurred from the same region of the Sun on June 4, 6, 9, and 11 in 1991. All four exhibited nuclear line emission in spectra from the EGRET energy calorimeter. Spectra from 1 to 200 MeV are given along with the time profile of the 2.22 and 4.4 Mev line intensities.

The flare on June 11 was especially significant in that the EGRET spark chamber detected emission to over 1000 MeV, and the time-scale of emission above 50 MeV persisted for 8 hours. An M-class flare 18 hours later produced a second increase above 50 MeV. The high energy spectra are well-fit by a combination of a bremsstrahlung and pion decay spectra. The time-scale of the bremsstrahlung component is as long or longer than the nuclear component suggesting that the acceleration process must be extended or episodic during the 8 hour period.

Program listing for Monday