A weak coronal heating event associated with periodic particle acceleration episodes

Weak heating events ($\sim\ 10^{17}$ -- $10^{20}$ J) are frequent and ubiquitous in the solar corona, but the underlying heating mechanism is still not very well understood. A major candidate for heating is weak flaring events which leave nearly undetectable signatures in the Extreme Ultra-Violet (EUV) and X-ray bands. However, since these events often lead to various plasma instabilities which produce coherent radiation at radio wavelengths, they can easily be detected and studied using radio imaging studies. But, often multiple such events happen on the Sun or these events get obscured by radio bursts that are several orders of magnitude stronger. With the advent of high dynamic range snapshot spectroscopic imaging, it has become possible to monitor such weak events continuously. Here we present a multi-waveband imaging study of an active region associated with a weak X-ray flare. We develop SPatially REsolved Dynamic Spectra (SPREDS) at metre-wavelength for the site. The SPREDS is combined with spatially resolved EUV and X-ray light curves of the region and magnetic field modelling. We detect a systematic evolution in the thermal energy of the region during the flare. This correlated well with the evolution in the mean coherent radio flux density and occurrence rate of bright second-scale coherent radio fine structures. The mean radio flux density light curve showed strong quasi periodic pulsations with a period of 30 s. We find that the timescale of the radio fine features match ion-electron collisional damping scale in the local plasma. The 30 s timescale matched the Alfv\'{e}n transit time in the radio source region. Our observations possibly support the picture of coronal heating via numerous faint flares/particle acceleration events which convert the magnetic free energy to heat. We find that the acceleration events are excited in a periodic manner with a periodicity of 30 s.