Radio Bursts Associated with Flare and Ejecta in the 13 July 2004 Event

TL;DR

This study analyzes radio bursts and associated coronal transients during a 2004 solar event, revealing complex interactions between flare, ejecta, and shock waves with implications for understanding solar radio emissions.

Contribution

It provides a detailed analysis of radio features and their relation to coronal shocks, highlighting the coexistence of blast-wave and CME-related radio emissions in a single event.

Findings

Radio continuum started before shock features appeared

Type II bursts linked to shock waves from flare and CME

Multiple radio features indicate complex shock interactions

Abstract

We investigate coronal transients associated with a GOES M6.7 class flare and a coronal mass ejection (CME) on 13 July 2004. During the rising phase of the flare, a filament eruption, loop expansion, a Moreton wave, and an ejecta were observed. An EIT wave was detected later on. The main features in the radio dynamic spectrum were a frequency-drifting continuum and two type II bursts. Our analysis shows that if the first type II burst was formed in the low corona, the burst heights and speed are close to the projected distances and speed of the Moreton wave (a chromospheric shock wave signature). The frequency-drifting radio continuum, starting above 1 GHz, was formed almost two minutes prior to any shock features becoming visible, and a fast-expanding piston (visible as the continuum) could have launched another shock wave. A possible scenario is that a flare blast overtook the earlier transient, and ignited the first type II burst. The second type II burst may have been formed by the same shock, but only if the shock was propagating at a constant speed. This interpretation also requires that the shock-producing regions were located at different parts of the propagating structure, or that the shock was passing through regions with highly different atmospheric densities. This complex event, with a multitude of radio features and transients at other wavelengths, presents evidence for both blast-wave-related and CME-related radio emissions.