Electron acceleration and capture in impulsive and gradual bursts: Results of analysis of microwave and hard x-ray emissions

A dynamic model is proposed that explains the relationship between microwave and hard x-ray (hx) emissions in impulsive and prolonged events (variation of intensity ratio, delay of maxima) without assuming additional shock-wave electron acceleration in prolonged bursts. According to this model, energetic electrons enter the burst arch for the entire duration of an hx flare. X-rays are generated chiefly as a thick target is approached, and, therefore, the duration is not a function of the background-plasma density and is determined only by the power of the particle source. On the other hand, microwave generation has a gyrosynchrotron mechanism, and, therefore, its intensity is determined by the instantaneous number of high-energy electrons accumulated in the trap. For the same maximum source power, the maximum number of accumulated electrons at the moment of the maximum onset must be directly related to the duration of electron injection and the lifetime of electrons in the trap. The results of this model are confirmed by new empirical regularities: the intensity ratio and delay of the maxima of the microwave and hx flares are increased monotonically with an increase in flare duration, and the nature of these relationships remains unchanged with transition from impulsive to prolonged flares