Low frequency observations of transient quasi-periodic radio emission from the solar atmosphere

TL;DR

This study reports low frequency observations of quasi-periodic, circularly polarized type III radio bursts near the solar limb, estimating the magnetic field strength in the active region corona using polarization and periodicity data.

Contribution

First measurement of magnetic field in the active region corona using low frequency radio burst polarization and periodicity analysis.

Findings

Magnetic field strength estimated at approximately 4.2 G.

Bursts exhibited a periodicity of about 5.2 seconds at 80 MHz.

Degree of circular polarization was approximately 0.12.

Abstract

We report low frequency observations of the quasi-periodic, circularly polarized, harmonic type III radio bursts whose associated sunspot active regions were located close to the solar limb. The measured periodicity of the bursts at 80 MHz was $\approx$ 5.2 s and their average degree of circular polarization ($dcp$) was $\approx 0.12$. We calculated the associated magnetic field $B$ : (1) using the empirical relationship between the $dcp$ and $B$ for the harmonic type III emission, and (2) from the observed quasi-periodicity of the bursts. Both the methods result in $B \approx$ 4.2 G at the location of the 80 MHz plasma level (radial distance $r \approx 1.3~\rm R_{\odot}$) in the active region corona.