1980 to 1989 Observations of Nuclear Gamma-Rays from Solar Flares

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We present a study of background-corrected spectra, 0.3 <= E_γ <=8.5 MeV, observed by the Gamma Ray Spectrometer on the Solar Maximum Mission satellite from 1980 to 1989. A total of 192 spectra covering the impulsive phases of these flares were fit by a model containing a power-law electron bremsstrahlung component and a nuclear component. The nuclear model was derived from the 1981 April 27 flare (Murphy et al. 1990). About 60\ the flares exhibit evidence for a nuclear component in addition to bremsstrahlung. We have summed spectra from flares into 16 groups according to their observed bremsstrahlung flux, extending over a dynamic range of 100. These summed spectra were fit once again with the two component model to compare average nuclear and bremsstrahlung emissions. The average nuclear and bremstrahlung fluxes are strongly correlated over the full range of study. On average we find evidence for nuclear emission even for the lowest range of bremsstrahlung fluxes observable >=300 keV ( ~ 5 times 10(-2) gamma cm(-2) s(-1) ). We also find that the average nuclear/bremsstrahlung ratio decreases and the average bremsstrahlung spectrum hardens with increasing heliocentric angle. This is consistent with earlier studies suggesting that the electrons producing the bremsstrahlung are not isotropically distributed. On the other hand the nuclear/bremsstrahlung ratio exhibits large scatter from flare to flare. A study of the temporal variations of the prompt nuclear and bremsstrahlung emissions, and of the delayed lines at 0.511 and 2.223 MeV, within individual flares is in progress. The nuclear/bremsstrahlung ratio exhibits significant variation during some of the flares. This work is supported under NASA DPR's W-17,972 and W-17,973. Murphy, R.J., et al. 1990, Ap. J., 358, 298.

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