Hard X-Ray Flares from the Sun

Abstract

A review of solar flare hard X-rays is presented. Various features of these flares have been considered to pinpoint the location of the source of emission and the nature of the emission of these flares. It is shown that the arguments for the location of the source in the dense chromosphere and against it are finely balanced, so that nothing conclusive may be said about the location of the source. Similarly, arguments for and against the non-thermal nature of the emission do not allow any definite conclusion at the present moment, through a belief persists that the hard X-ray emission is nonthermal in nature. Theories of non-thermal X-ray emission are briefly considered and it has been suggested that a combination of emission mechanisms may be needed to explain the complete energy spectrum of hard X-rays.