Gamma-Ray Line Versus Continuum Emission of Electron-Dominated Episodes During Solar Flares

Electron-dominated episodes or events during solar flares are characterized by a flattening of the electron bremsstrahlung continuum above about 1 MeV. This flattening leads to a dominance of the continuum at MeV energies over nuclear emissions. We analyzed events recorded by the gamma-ray spectrometer on SMM with the aim to determine the nuclear contribution in the energy range between 4 and 8 MeV. We find that for comparable continuum fluences it is less by about an order of magnitude than for other flares. The spectral index of the best-fit power law of the > 1 MeV continuum with a median at –1.84 turns out to be independent of the heliocentric angle of the events, implying that the degree of anisotropy of the radiating particles was low. It is of interest to note that a value of –1.5 seems to be a limit. The spectral index of the continuum between 0.3 and 1 MeV does not differ significantly from that of other flares. Only measurements with detectors sensitive up to at least 10 MeV can, therefore, sort out electron dominated episodes during solar flares.