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

TL;DR

This study presents simultaneous low-frequency radio, X-ray, and EUV observations of weak energy releases in the quiet Sun, revealing correlated transient activities and highlighting the importance of coordinated multi-wavelength observations for understanding solar phenomena.

Contribution

It provides rare simultaneous observations of weak radio, X-ray, and EUV emissions from the quiet Sun, demonstrating their temporal correlation and emphasizing the need for coordinated multi-wavelength solar studies.

Findings

Type I radio bursts associated with weak X-ray flares.

Brightness temperature of radio bursts around 3×10^5 K.

Correlated EUV brightenings near radio burst locations.

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 $\rm {<}10^{-7}\,Wm^{-2}$ in the 1\,-\,8\,$\rm {\AA}$ 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 94{\AA} 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.