Hard X-ray and Radio Emission at the Onset of Great Solar Flares

Abstract

A study of the onset phase of ten great hard X-ray bursts is presented. It is shown from hard X-ray and radio observations in different wavelength ranges that the energization of the electrons proceeds on a global time-scale of some tens of seconds. In nine of the bursts two phases of emission can be distinguished during the onset phase: the pre-flash phase, during which emission up to an energy limit ranging from some tens of keV to 200 keV is observed, followed ten to some tens of seconds later by the flash phase, where the count rate in all detector channels rises simultaneously to within some seconds. For two of the events strong γ-ray line emission is observed and is shown to start close to the onset of the flash phase.

Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.