Evidence for Super-Alfvenic oscillations in sources of Solar type III radio bursts

TL;DR

This study presents the first observational evidence of super-Alfvenic oscillations in solar type III radio burst sources, revealing rapid, large-scale source size and orientation oscillations linked to a quasi-periodic regulation mechanism at the particle injection site.

Contribution

It introduces a novel method to analyze weak solar radio bursts and provides the first evidence of super-Alfvenic oscillations in burst sources, challenging existing MHD interpretations.

Findings

Detection of second-scale QPOs in source sizes and orientations.

Evidence for super-Alfvenic oscillations requiring higher Alfven speeds.

Identification of systematic drift in burst source locations.

Abstract

At the site of their origin, solar meterwave radio bursts contain pristine information about the local coronal magnetic field and plasma parameters. On its way through the turbulent corona, this radiation gets substantially modified due to the propagation effects. Effectively disentangling the intrinsic variations in emission from propagation effects has remained a challenge. We demonstrate a way to achieve this, using snapshot spectroscopic imaging study of weak type III bursts using data from the Murchison Widefield Array (MWA). We use this study to present the first observational evidence for second-scale Quasi-Periodic Oscillations (QPOs) in burst source sizes and orientation with simultaneous QPOs in intensity. The observed oscillations in source sizes are so fast and so large that, they would require two orders of magnitude larger Alfven speed than the typical 0.5 Mm/s, if interpreted within a MHD framework. These observations imply the presence of a quasi-periodic regulation mechanism operating at the particle injection site, modulating the geometry of energetic electron beams that generate type III bursts. In addition, we introduce a method to characterize plasma turbulence in mid coronal ranges, using such frequent weak bursts. We also detect evidence for a systematic drift in the location of the burst sources superposed on the random jitter induced by scattering. We interpret this as the motion of the open flux tube within which the energetic electron beams travel.