Fine structure of the sources of quasi-periodic pulsations in “single-loop” solar flares

Abstract

Analysis of the observational data obtained with a high angular resolution in the ranges of vacuum ultraviolet (1″, TRACE) and hard X-ray (4″, RHESSI) emissions in some solar flares previously considered “single-loop” ones shows that they are not such flares. The thick single loops with a diameter of 13″–21″ observed in these flares in the microwave range with an angular resolution of 5″–10″ (NoRH) are actually arcades of thinner loops with a diameter of less than 3″. In this case, the observed quasi-periodic pulsations of microwave emission are not a consequence of the oscillations of an isolated thick loop, as is usually assumed, but a result of the successive involvement of many relatively thinner loops in the process of flare energy release. The established facts impose significant constraints on the generation models of pulsations in flares.