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High-Energy Particle Production in Solar Flares (SEP, Gamma-Ray and Neutron Emissions)

Electrons and ions, over a wide range of energies, are produced in association with solar flares. Solar energetic particles (SEPs), observed in space and near Earth, consist of electrons and ions that range in energy from 10 keV to ∼ 100 MeV and from 1 MeV to 20 GeV, respectively. SEPs are directly recorded by charged particle detectors, while x-ray, γ-ray, and neutron detectors indicate the properties of the accelerated particles (electrons and ions) which have interacted in the solar atmosphere. A major problem of solar physics is to understand the relationship between these two groups of charged particles; in particular whether they are accelerated by the same mechanism. We review the physics of γ-ray and neutron production in the solar atmosphere and the method by which properties of the primary charged particles produced in the solar flare can be deduced. Recent observations of energetic photons and neutrons in space and at the Earth are used to present a current picture of the properties of impulsively flare accelerated electrons and ions. Some important properties discussed are time scale of production, composition, energy spectra, accelerator geometry. The correlation of the SEP flux with the yield of γ-rays at the Sun is briefly discussed. We review, in some detail, energetic particle production in the large flare on 1982 June 3. Discussed also are gamma ray and neutron observational constraints on particle acceleration mechanisms and a summary of some recent work on solar flare particle acceleration mechanisms.