Three-dimensional reconstruction of type U radio bursts: a novel remote sensing approach for coronal loops

TL;DR

This paper introduces a novel method using high-resolution radio images to accurately reconstruct the 3D structure of coronal loops from type U radio bursts, providing insights into electron beam dynamics and plasma mechanisms.

Contribution

It demonstrates that radio heliograph images alone can reconstruct coronal loop morphology and constrain physical parameters without triangulation, advancing remote sensing techniques.

Findings

Successful 3D reconstruction of coronal loops from radio images.

Insights into electron beam acceleration and plasma mechanisms.

Explanation for the lack of EUV-radio loop association.

Abstract

Type U radio bursts are impulsive coherent radio emissions produced by the Sun that indicate the presence of subrelativistic electron beams propagating along magnetic loops in the solar corona. In this work, we present the analysis of a type U radio burst that was exceptionally imaged on 2011 March 22 by the Nan\c{c}ay Radioheliograph (NRH) at three different frequencies (298.7, 327.0, and 360.8 MHz). Using a novel modelling approach, we show for the first time that the use of high-resolution radio heliograph images of type U radio bursts can be sufficient to both accurately reconstruct the 3D morphology of coronal loops (without recurring to triangulation techniques) and to fully constrain their physical parameters. At the same time, we can obtain unique information on the dynamics of the accelerated electron beams, which provides important clues as to the plasma mechanisms involved in their acceleration and as to why type U radio bursts are not observed as frequently as type III radio bursts. We finally present plausible explanations for a problematic aspect related to the apparent lack of association between the modeled loop as inferred from radio images and the extreme-ultraviolet (EUV) structures observed from space in the same coronal region