A Weak Coronal Heating Event Associated with Periodic Particle Acceleration Episodes

Weak heating events are frequent and ubiquitous in the solar corona. They derive their energy from the local magnetic field and form a major source of local heating, signatures of which are seen in EUV and X-ray bands. Their radio emission arises from various plasma instabilities that lead to coherent radiation, making even a weak flare appear very bright. Hence, the radio observations probe nonequilibrium dynamics, providing complementary information on plasma evolution. However, a robust study of radio emission from a weak event among many simultaneous events requires high dynamic range imaging at subsecond and sub-MHz resolutions owing to its high spectrotemporal variability. Such observations were not possible until recently. This is among the first spatially resolved multiwaveband studies of active region loops hosting transient brightenings (ARTBs) and is dynamically linked to meter-wave type I noise storms. Observations at meter-wave, EUV, and X-ray bands are used, along with magnetogram data. We believe that this is the first spectroscopic radio imaging study of a type I source, the data for which were obtained using the Murchison Widefield Array. We report the discovery of 30 s quasi-periodic oscillations (QPOs) in the radio light curve riding on a coherent baseline flux. The strength of the QPOs and the baseline flux were enhanced during a microflare associated with the ARTB. Our observations suggest a scenario where magnetic stress builds up over an Alfvén timescale (30 s) across the typical magnetic field braiding scale and then dissipates via a cascade of weak reconnection events.