A Statistical Study of Low-frequency Solar Radio Type-III Bursts

TL;DR

This study statistically analyzes low-frequency solar radio Type-III bursts observed over four years, examining their properties, associations with solar flares, and directional origins, revealing that high-frequency bursts predominantly originate from western longitudes.

Contribution

It provides a comprehensive statistical analysis of Type-III bursts, including their frequency cut-offs, flare associations, and directional origins, which was not extensively studied before.

Findings

High-frequency bursts (>350 MHz) mainly originate from western longitudes.

Western longitudes have a higher number of bursts reaching Earth.

Most bursts are associated with solar flares, but some are triggered by small-scale features.

Abstract

We have studied low-frequency (45 - 410 MHz) type III solar radio bursts observed using the e-CALLISTO spectrometer located at Gauribidanur radio observatory, India during 2013 - 2017. After inspecting the 1531 type III bursts we found that 426 bursts were associated with flares, while the other bursts might have triggered by small scale features / weak energy events present in the solar corona. In this study, we have carried out a statistical analysis of various observational parameters like start time, lower and upper-frequency cut-offs of type III bursts and their association with flares, variation of such parameters with flare parameters such as location, class, onset and peak timings. From this study, we found that most of the high-frequency bursts (whose upper-frequency cut-off $> 350$ MHz) are originated from the western longitudes. We interpret that it could be due to the fact that Parker spirals from these longitudes are directed towards the earth and high-frequency bursts are more directive. Further, we report that number of bursts that reach earth from western longitudes are higher than eastern longitudes.