Background Microwave Emission and Microflares in Young Active Region 12635

Abstract

Abstract The goal of this work is to study the atmospheric heating above isolated AR 12635 during a period in which a quasistationary increase in microwave and soft X-ray emission is combined with a series of B- and C-class microflares. Analysis of photospheric vector magnetograms showed that an increase in the SXR brightness lasting 14 hours was observed during the simplification of the magnetic structure and the growth of vertical currents in the head part of the active region. A long-term increase of SXR and microwave emission occurred when the total unsigned vertical current exceeded the critical value and coincided in time with the increased level of the emission measure calculated from the GOES X-ray data. Against the background of quasistationary emission, microflares lasting 6–10 minutes occurred. In the hard X-ray range, bursts are recorded with RHESSI channels up to 25 keV. In microwave emission, pulsed and smooth components are distinguished during microflares. The first component was recorded in the 4.5–7.5 GHz range at the beginning of microflares and it is generated by a small population of relativistic electrons by the gyrosychrotron mechanism. The smooth component of the bursts dominated at 17 GHz and was emitted by bremsstrahlung. It is shown that the sources of quasistationary emission and microflares coincide with each other and with the bremsstrahlung source calculated from the differential emission measure obtained from the EUV maps. Coronal magnetic field reconstruction shows that the release of energy on both timescales occurs in a stably existing bundle of magnetic field lines.