Siberian Radioheliograph: sunspot oscillations in 3–6 GHz band

Abstract

ABSTRACT We present the first observations of spatially resolved oscillation sources obtained with the Siberian Radioheliograph at 3–6 GHz. We have found significant flux oscillations with periods of about 3, 5, and 13 min emitted from AR12833. The 3-min periodicity dominates at higher frequencies. It was found that the apparent level of oscillations depends on the active region location on the disc, and scales down towards the limbs. The oscillations were studied in detail during 1 h interval on 2021 June 19. We found that sources of 3-min oscillations were located above the umbra and their emission is extraordinary polarized. The 5- and 13-min periods were manifested in emission at lower frequencies, down to 2.8 GHz. Sources with 5-min periodicity were located near the umbra/penumbra boundary and in the pore region. Positions of sources with 13-min oscillations were different at 3.1 and 4.7 GHz. We found consistency between spatial location of the oscillation sources in radio and ultraviolet at 171 and 304 Å. There is significant correlation of signals in two ranges. Time delays between microwave oscillations increase as the frequency decreases, which can be explained by upward propagation of periodic disturbances. The localization of oscillation sources is probably related to magnetic structures with different wave cut-off frequencies at different heights.