HIGH-ENERGY GAMMA-RAY EMISSION FROM SOLAR-FLARES - CONSTRAINING THE ACCELERATED PROTON SPECTRUM

Using a multi-component model to describe the gamma-ray emission, we i nvestigate the flares of December 16,1988 and March 6,1989 which exhib ited unambiguous evidence of neutral pion decay. The observations are then combined with theoretical calculations of pion production to cons train the accelerated proton spectra. The detection of pi0 emisson alo ne can indicate much about the energy distribution and spectral variat ion of the protons accelerated to pion producing energies. Here both t he intensity and detailed spectral shape of the Doppler-broadened pi0 decay feature are used to determine the spectral form of the accelerat ed proton energy distribution. The Doppler width of this gamma-ray emi ssion provides a unique diagnostic of the spectral shape at high energ ies, independent of any normalisation. To our knowledge, this is the f irst time that this diagnostic has been used to constrain the proton s pectra. The form of the energetic proton distribution is found to be s everely limited by the observed intensity and Doppler width of the pi0 decay emission, demonstrating effectively the diagnostic capabilities of the pi0 decay gamma-rays. The spectral index derived from the gamm a-ray intensity is found to be much harder than that derived from the Doppler width. To reconcile this apparent discrepancy we investigate t he effects of introducing a high-energy cut-off in the accelerated pro ton distribution. With cut-off energies of around 0.5-0.8 GeV and rela tively hard spectra, the observed intensities and broadening can be re produced with a single energetic proton distribution above the pion pr oduction threshold.