Electron acceleration in impulsive solar flares

Physical parameters relevant to the acceleration and propagation of energetic electrons during the impulsive phase of a solar flare are studied in hard X-ray, microwave and both type III and decimetric radio bursts associated with the December 4, 1978 solar flare. A one-to-one association between single type III bursts and hard X-ray peaks is established, along with a burst delay with respect to the peaks of 0.5 sec. The observed increase of the high frequency cutoff of the metric type III bursts during the impulsive phase is examined in terms of the decreasing altitude of the electron acceleration/injection region, increasing electron spectrum hardness, and decreasing acceleration time. A pulsating decimetric continuum was found to be present during and before the impulsive phase whose high frequency cutoff also systematically increased during the rise of the impulsive phase.