A Weak Coronal Heating Event Associated with Periodic Particle Acceleration Episodes

Abstract

Weak heating events are frequent and ubiquitous in 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 arise from various plasma instabilities that lead to coherent radiation, making even a weak flare appear very bright. The radio observations hence probe non-equilibrium 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 sub-second and sub-MHz resolutions owing to their high spectro-temporal variability. Such observations were not possible until recently. This is among the first spatially resolved studies of an active region loop hosting a transient brightening (ARTB) and dynamically linked to a metrewave type-I noise storm. It uses imaging observations at metrewave, EUV and X-ray bands, along with magnetogram data. We believe this is the first spectroscopic radio imaging study of a type-I source, the data for which was 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 enhanced during a mircoflare associated with the ARTB. Our observations suggest a scenario where magnetic stress builds up over an Alfvén timescale (30s) across the typical magnetic field braiding scale and then dissipates via a cascade of weak reconnection events.

A search for counterparts of quiet sun radio transients in extreme ultraviolet data

“…The energy variation in the system also follows a similar trend. This is exactly what was observed by Mohan et al (2019a). Based on this additional evidence, I present a physical model below.…”

“…Recent simulations also hint towards a relationship between the two phenomena. Chen et al (2021) found three magnetic field orientations which can produce campfires and one of them match almost exactly with the emission geometry found in Mohan et al (2019a) and Mohan (2021). Future studies with simultaneous observations with the Solar Orbiter and sensitive radio interferometers will be able to investigate possible relationships between these two phenomena in detail.…”

“…M20 hypothesised that WINQSEs are the weaker cousins of the emissions observed by Mohan et al (2019a). Here I present strong evidence, albeit in a two groups of WINQSEs, that the smoothed radio light curve shows variation at very similar timescales as its EUV counterpart.…”

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“…Quasiperiodic oscillation in the radio lightcurve was seen from the sun in which the period was associated with the timescale in which magnetic stress is built up and then relieved through reconnection (e.g. Mohan et al 2019).…”

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“…These observations cannot be explained in terms of the conventional Alfvènic oscillations. In the same data set, Mohan et al (2019a) also find an unrelated weak flare seen in the EUV and soft X-rays. Their analysis shows that this flare was responsible for some local coronal heating.…”