Fast time structures superimposed to impulsive solar microwave bursts with slowly varying or stationary polarization degree

TLDR: In this paper, the authors analyzed 7 GHz bursts with a time constant of 100 ms and showed that the microwave fast component burst source might remain nearly stationary in relation to the polarizing medium, occupying the same position as the active center hot spot previous to the event.

Abstract: The ultimate definition of fast time structures superimposed on an impulsive solar microwave burst is limited by instrumental time resolution and sensitivity. We analysed 7 GHz bursts with a time constant of 100 ms. The fast time structures seem to be common to all events, although the resolution so far attained might still be smoothing out structures with finer scale. The polarization degree does not show corresponding fast changes. When the degree of circular polarization is referred to the burst's excess flux, it may show a slowly varying time development. When it is referred to the total active center contribution, the polarization degree might become nearly unchanged during the burst development. The polarization degree is set by the large scale magnetic field strength and morphology over the active center and the burst source. The present results suggest that the microwave fast component burst source might remain nearly stationary in relation to the polarizing medium, occupying the same position as the active center hot spot previous to the event. The absence of fast time structures in polarization degree indicate negligible fast changes in the large scale magnetic field which pervades the burst source. Slow changes in polarization degree are sometimes associated with the slow component of impulsive events, and might be representative of secondary accelerations interpreted in terms of trap models. We discuss qualitatively some energy conversion mechanisms based on turbulent processes which may account for the fast burst components.