Microwave response to sunspot oscillations

TL;DR

This study presents the first spatially resolved microwave observations of sunspot oscillations using SRH, revealing distinct periodicities and their association with magnetic structures and UV counterparts.

Contribution

It provides new spatially resolved microwave data of sunspot oscillations at 3-6 GHz, linking radio sources with magnetic structures and UV observations for the first time.

Findings

3-minute oscillations dominate at higher frequencies

Oscillation sources are located above the umbra with extraordinary polarization

Time delays suggest upward propagation of disturbances

Abstract

We present the first observations of spatially resolved oscillation sources obtained with the Siberian Radioheliograph (SRH) at 3-6 GHz. We have found significant flux oscillations with periods of about 3, 5 and 13 minutes emitted from AR12833. The 3-minute 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 one hour interval on June 19, 2021. 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 GHz and 4.7 GHz. We found consistency between spatial location of the oscillation sources in radio and UV in 171A and 304A. 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 cutoff frequencies at different heights. The obtained results show that SRH can provide the spatial resolved observation of the oscillations in the intensity and polarization channels in 3-6 GHz band.