Fundamental-harmonic pairs of interplanetary type III radio bursts

TL;DR

This paper presents the first detailed observations of fundamental-harmonic pairs of interplanetary type III radio bursts in hecto-kilometric wavelengths, providing new insights into their spectral and polarization characteristics using Parker Solar Probe data.

Contribution

It reports novel detailed observations and analysis of fundamental-harmonic pairs of type III radio bursts in the interplanetary medium, which were previously difficult to detect and analyze.

Findings

Fundamental-harmonic pairs constitute the majority of observed type III bursts during close encounters.

Measured time-delay and asymmetry provide insights into emission processes.

Polarization analysis enhances understanding of burst characteristics.

Abstract

Type III radio bursts are not only the most intense but also the most frequently observed solar radio bursts. However, a number of their defining features remain poorly understood. Observational limitations, such as a lack of sufficient spectral and temporal resolution, have hindered a full comprehension of the emission process, especially in the hecto-kilometric wavelengths. Of particular difficulty is the ability to detect the harmonics of type III radio bursts. Hereafter we report for the first detailed observations of type III fundamental-harmonic pairs in the hecto-kilometric wavelengths, observed by the Parker Solar Probe. We present the statistical analysis of spectral characteristics and the polarization measurements of the fundamental-harmonic pairs. Additionally, we quantify various characteristic of the fundamental-harmonic pairs, such as the time-delay and time-profile asymmetry. Our report and preliminary analysis conclude that fundamental-harmonic pairs constitute a majority of all type III radio bursts observed during close encounters 6 -- 10 when the probe is in close proximity to the source region and propagation effects are less pronounced.