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 ove r nuclear emissions. We analyzed events recorded by the gamma-ray spectrome ter 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 spectr al index of the best-fit power law of the > 1 MeV continuum with a median a t - 1.84 turns out to be independent of the heliocentric angle of the event s, implying that the degree of anisotropy of the radiating particles was lo w. It is of interest to note that a value of similar to -1.5 seems to be a limit. The spectral index of the continuum between 0.3 and 1 MeV does not d iffer significantly from that of other flares. Only measurements with detec tors sensitive up to at least 10 MeV can, therefore, sort out electron domi nated episodes during solar flares.