Properties of Type III and Type IIIb Bursts in the Frequency Band of 8-80 MHz during PSP Perihelion at the Beginning of April 2019

TL;DR

This study analyzes the properties of type III and IIIb solar radio bursts in the 8-80 MHz range during PSP perihelion, revealing their drift rates, durations, and relation to coronal conditions, with implications for solar physics.

Contribution

It provides new observational data on type III and IIIb bursts during PSP perihelion and compares their properties with coronal models, highlighting differences in their frequency dependences.

Findings

Drift rate dependences align with Newkirk corona for source velocities 0.17-0.2 c.

Durations and drift rates differ significantly between type III and IIIb bursts.

Observed dependencies are flatter than those predicted by standard coronal models.

Abstract

Properties of type III and type IIIb bursts in the frequency band of 8-80 MHz observed by the radio telescopes Ukrainian Radio Interferometer of NASU-2 (URAN-2) (Poltava) and Giant Ukrainian Radio Telescope (GURT) (Kharkiv) during the Parker Solar Probe (PSP) perihelion in April 2019 are discussed. These correspond of those that were observed by PSP at frequencies <19 MHz. We analyze dependences of drift rates and durations on frequency for these bursts. We show that drift rate dependences on frequency agree well with those derived from the Newkirk corona if source velocities are between 0.17 and 0.2 c for both type IIIb bursts and type III bursts under the assumption that the first ones are fundamentals and the second ones are their harmonics. However, all observational dependences are flatter in comparison with the dependences for a Newkirk corona. We assume that this can be related with coronal temperature decreasing at heliocentric distances from 1.35 to 6.5 solar radii. Duration dependencies of type IIIb and type III bursts on frequency in the range of 10-70 MHz are also obtained. We note that the durations and drift rates of type III bursts as well as their dependences on frequency differ essentially from those for type IIIb bursts.