The SEP matter sample and its correlation with gamma-ray observations
The current state of Solar Energetic Particle (SEP) observations above ∼ 1 MeV nucl.-1 is examined and compared to gamma-ray observations to assess the degree to which current understanding of the solar flare process can explain the observations and to delineate directions for future research. The particle acceleration appears to be due to either Fermi-type stochastic processes or flare-generated shock waves, but the available data can not yet distinguish between these two mechanisms. Large SEP events generally show no gamma-ray emission and may be examples of shock acceleration in the corona. The pre-accelerated matter, however, seems to be a mixture of hot (> 106 K) and cold (< 105 K) plasma with an elemental composition enriched with respect to the photosphere in ions of low first ionization potential (< 10 eV) and sometimes enhanced in heavy ions (Z > 10). These enrichments may be due to thermal/ pressure gradient diffusion and neutral gravitational settling. Gamma-ray line emission events are often associated with small, 'electron rich' SEP events, some of which also include heavy ion enhancements. While time profiles of the gamma emission show that electrons and ions can be accelerated promptly (t < 1 s), comparison of the inferred flux of particles at the Sun with SEP observations in space indicate that few of these particles escape. The conditions for SEP release to interplanetary space have yet to be systematically detailed. © 1988 Kluwer Academic Publishers.