Detection of Ubiquitous Weak and Impulsive Nonthermal Emissions from the Solar Corona

Abstract

Abstract A ubiquitous presence of weak energy releases is one of the most promising hypotheses to explain coronal heating, referred to as the nanoflare hypothesis. The accelerated electrons associated with such weak heating events are also expected to give rise to coherent impulsive emission via plasma instabilities in the meterwave radio band, making this a promising spectral window to look for their presence. Recently Mondal et al. reported the presence of weak and impulsive emissions from quiet Sun regions which seem to meet the requirements of being radio counterparts of the hypothesized nanoflares. Detection of such low-contrast weak emission from the quiet Sun is challenging and, given their implications, it is important to confirm their presence. In this work, using data from the Murchison Widefield Array, we explore the use of an independent robust approach for their detection by separating the dominant, slowly varying component of emission from the weak impulsive one in the visibility domain. We detect milli-Solar Flux Unit-level bursts taking place all over the Sun and characterize their brightness temperatures, distributions, morphologies, durations, and associations with features seen in extreme-UV images. We also attempt to constrain the energies of the nonthermal particles using inputs from the FORWARD coronal model along with some reasonable assumptions, and find them to lie in the subpico flare (∼1019–1021 erg) range. In the process, we also discover perhaps the weakest type III radio burst and another that shows clear signatures of the weakest quasi-periodic pulsations.