Imaging and Spectral Observations of a Type-II Radio Burst Revealing the Section of the CME-Driven Shock that Accelerates Electrons

TL;DR

This study combines multi-wavelength observations to identify the CME flank as the source of a Type-II radio burst, revealing details about shock acceleration regions during a solar eruption.

Contribution

It provides new evidence that the Type-II radio emission originates from the CME flanks, especially the southern flank, based on imaging and spectral analysis.

Findings

Type-II burst linked to CME flanks, especially the southern flank.

Shock speed and Alfvén speed are closely matched at the CME nose.

Streamer presence near the flank facilitates shock-associated radio emission.

Abstract

We report on a multi-wavelength analysis of the 26 January 2014 solar eruption involving a coronal mass ejection (CME) and a Type-II radio burst, performed by combining data from various space-and ground-based instruments. An increasing standoff distance with height shows the presence of a strong shock, which further manifests itself in the continuation of the metric Type-II burst into the decameter-hectometric (DH) domain. A plot of speed versus position angle (PA) shows different points on the CME leading edge travelled with different speeds. From the starting frequency of the Type-II burst and white-light data, we find that the shock signature producing the Type-II burst might be coming from the flanks of the CME. Measuring the speeds of the CME flanks, we find the southern flank to be at a higher speed than the northern flank; further the radio contours from Type-II imaging data showed that the burst source was coming from the southern flank of the CME. From the standoff distance at the CME nose, we find that the local Alfven speed is close to the white-light shock speed, thus causing the Mach number to be small there. Also, the presence of a streamer near the southern flank appears to have provided additional favorable conditions for the generation of shock-associated radio emission. These results provide conclusive evidence that the Type-II emission could originate from the flanks of the CME, which in our study is from the the southern flank of the CME.