Radio, X-ray and extreme-ultraviolet observations of weak energy releases in the `quiet' Sun

Abstract

We analyzed ground-based low frequency ($<$100\,MHz) radio spectral and imaging data of the solar corona obtained with the facilities in the Gauribidanur observatory during the same time as the very weak soft X-ray flares (sub A-class, flux $<10^{-7}\mathrm{W}{\mathrm{m}}^{-2}$ in the 1\,-\,8\,$\mathring{\mathrm{A}}$ wavelength range) from the `quiet' Sun observed with the X-ray Solar Monitor (XSM) onboard Chandrayaan-2 during the recent solar minimum. Non-thermal type I radio burst activity were noticed in close temporal association with the X-ray events. The estimated brightness temperature ($T_b$) of the bursts at a typical frequency like 80\,MHz is $\approx 3\times 10^5$\,K. Extreme-ultraviolet (EUV) observations at 94Å with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) revealed a brightening close to the same location and time as the type I radio bursts. As far as we know reports of simultaneous observations of X-ray and/or EUV counterpart to weak transient radio emission at low frequencies from the `quiet' Sun in particular are rare. Considering this and the fact that low frequency radio observations are sensitive to weak energy releases in the solar atmosphere, the results indicate that coordinated observations of similar events would be useful to understand transient activities in the `quiet' Sun.

Published in Astrophysical Journal Letters, 6 pages, 4 figures

References in corpus (7)

• An estimate of the magnetic field strength associated with a solar coronal mass ejection from low frequency radio observations
• Solar X-ray Monitor On Board the Chandrayaan-2 Orbiter: In-flight Performance and Science Prospects
• First radio evidence for impulsive heating contribution to the quiet solar corona
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• Low frequency radio observations of the `quiet' corona during the descending phase of sunspot cycle 24

Cited by in corpus (1)

• Detection of weak ubiquitous impulsive nonthermal emissions from the solar corona