An unsupervised machine learning based algorithm for detecting Weak Impulsive Narrowband Quiet Sun Emissions and characterizing their morphology

TL;DR

This paper introduces a machine learning algorithm to detect and analyze Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs), revealing their morphology and suggesting they are affected by coronal scattering, thus offering new insights into coronal turbulence.

Contribution

The work develops a novel unsupervised machine learning method for detecting and characterizing WINQSEs, improving detection accuracy and morphological analysis over previous techniques.

Findings

WINQSEs are often resolved, indicating angular broadening due to coronal scattering.

The algorithm successfully detects WINQSEs across multiple datasets.

WINQSEs can serve as diagnostics for coronal turbulence.

Abstract

The solar corona is extremely dynamic. Every leap in observational capabilities has been accompanied by unexpected revelations of complex dynamic processes. The ever more sensitive instruments now allow us to probe events with increasingly weaker energetics. A recent leap in the low-frequency radio solar imaging ability has led to the discovery of a new class of emissions, namely Weak Impulsive Narrowband Quiet Sun Emissions \citep[WINQSEs;][]{mondal2020}. They are hypothesized to be the radio signatures of coronal nanoflares and could potentially have a bearing on the long standing coronal heating problem. In view of the significance of this discovery, this work has been followed up by multiple independent studies. These include detecting WINQSEs in multiple datasets, using independent detection techniques and software pipelines, and looking for their counterparts at other wavelengths. This work focuses on investigating morphological properties of WINQSEs and also improves upon the methodology used for detecting WINQSEs in earlier works. We present a machine learning based algorithm to detect WINQSEs, classify them based on their morphology and model the isolated ones using 2D Gaussians. We subject multiple datasets to this algorithm to test its veracity. Interestingly, despite the expectations of their arising from intrinsically compact sources, WINQSEs tend to be resolved in our observations. We propose that this angular broadening arises due to coronal scattering. WINQSEs can, hence, provide ubiquitous and ever-present diagnostic of coronal scattering (and, in turn, coronal turbulence) in the quiet sun regions, which has not been possible till date.