Gamma ray lines from solar flares and cosmic transients

Gamma ray line emission processes in solar flares and cosmic transients are reviewed and implications of recent line observations are discussed. The gamma ray line emission from solar flares results from nuclear interactions of accelerated particles with the solar atmosphere. The observed line intensities give information on the total number and spectrum of particles accelerated in the flare, on the temperature and density in the interaction regions and on the time history of the interactions. Analysis of the line observations from the June 7, 1980, flare show that the number of protons accelerated in the flare exceeded the number observed in the interplanetary medium by a factor of ~100. The bulk of the accelerated protons, therefore, remained trapped in the solar atmosphere where they produced gamma ray line emission as they slowed down.

The gamma ray emission lines observed from gamma ray transients appear to result from both the annihilation of positrons produced in photon-photon interactions and from deexcitation of nuclear levels and capture of neutrons produced in nuclear interactions. The observed line intensity provides information on the temperature, density, composition, magnetic field and redshift in the transient sources. Both the gravitational redshift and the iron enrichment implied by the gamma ray line observations strongly suggest that neutron stars are the source of the transients.