What High Energy Emissions Reveal about Solar Flares

Interactions of accelerated ions in solar flares produce gamma-ray lines and continuum and neutrons. These emissions contain a rich set of observable quantities such as line intensities, shapes, shifts and time histories and escaping neutron spectra and time histories. An extensive database of high-energy flare observations spanning almost 25 years exists from various missions such as SMM/GRS, Yohkoh, all four CGRO instruments, GAMMA-1, and GRANAT/Phebus. RHESSI, launched in 2002, observed the 2002 July 23 solar flare and provided the first comprehensive high-spectral resolution measurements and gamma-ray imaging of a flare and has since observed gamma-ray lines from the 2003 October 28 and November 2 flares. These high-energy measurements provide information not only about the accelerated particles but also about the physical conditions at the flare site. We will discuss how this information is extracted from the measurements and review what has been learned about the acceleration process, the relationship of flare particles with particles observed in space, and the flare environment.