Average Temporal Profiles of Solar Flare Microwave Emission: Morphology and Application

Abstract

Both solar and stellar average temporal profiles of emission demonstrate general laws of evolution of such complex and diverse phenomenon as flare. Empirically obtained average profiles for events with simple dynamic make it possible both to analyze the emission mechanisms of solar and stellar flares and to help to divide complex events into discrete acts of energy release. Microwave emission is of particular interest, since it can reflect the precipitation dynamics of accelerated electrons. For the reconstruction of average time profiles. We selected 116 observed with the Siberian Radioheliograph observations in the range of 3‒24 GHz. These profiles have demonstrated a simple time structure and a broadband gyrosynchrotron spectrum of non-thermal nature. The wide spectral range allowed to divide emission into emission of optically thick and optically thin sources. The time profiles that describe the emission from different regions of the flare loop have been summed within the respective spectral band, after which for each event, normalization and time scaling have been applied. The average time profiles have been obtained as the median value for each time bin (step). As a result, it has been shown that the microwave average time profiles for the microwave optically thick and thin sources are identical for a solar flare with simple dynamics. This indicates the dominance of accelerated electron precipitation processes in the emission of such events. Also, the dominance of non-thermal processes for this type of event has been confirmed by a comparison with the results of a solar-flare dynamics modelling in the 304 Å line obtained in studies of other authors and an analysis of the dynamics of microwave emission during the decay phase. Analytical functions that describe the rise and decay phases of microwave emission of solar-flare have been obtained. The use of analytical functions in combination with the average time profile for the analysis of the February 3, 2022 event has shown the possibility of using this method to separate the acts of energy release associated with the precipitation of accelerated electrons. The obtained average time profiles, as well as analytical functions describing the behaviour of simple solar-flare microwave emission, can be used both to analyze the emission of solar events in the microwave range and to study the processes occurring during stellar flares.