Diagnostics on the source properties of type II radio burst with spectral bumps

TL;DR

This study links spectral bumps in type II radio bursts to CME-shock interactions with dense streamers, revealing localized emission sources and shock geometries through combined radio and imaging observations.

Contribution

It extends previous work by analyzing a specific CME event with spectral bumps, demonstrating their origin from shock-streamer interactions and localized emission regions.

Findings

Spectral bumps correspond to CME-shock crossing dense streamers.

Type II emissions originate from spatially confined sources less than 0.1 R☉.

Shock geometries at emission sites are likely quasi-perpendicular or oblique.

Abstract

In recent studies (Feng et al., 2012; Kong et al., 2012), we proposed that source properties of type II radio bursts can be inferred through a causal relationship between the special shape of the type II dynamic spectrum (e.g., bump or break) and simultaneous extreme ultraviolet (EUV)/white light imaging observations (e.g., CME-shock crossing streamer structures). As a further extension of these studies, in this paper we examine the CME event dated on December 31 2007 associated with a multiple type II radio burst. We identify the presence of two spectral bump features on the observed dynamic spectrum. By combining observational analyses of the radio spectral observations and the EUV-white light imaging data, we conclude that the two spectral bumps are resulted from CME-shock propagating across dense streamers on the southern and northern sides of the CME, respectively. It is inferred that the corresponding two type II emissions originate separately from the two CME-shock flanks where the shock geometries are likely quasi-perpendicular or oblique. Since the emission lanes are bumped as a whole within a relatively short time, it suggests that the type IIs with bumps of the study are emitted from spatially confined sources (with a projected lateral dimension smaller than 0.05-0.1 R$_\odot$ at a fundamental frequency level of 20-30 MHz).