A broken solar type II radio burst induced by a coronal shock propagating across the streamer boundary

TL;DR

This paper analyzes a solar type II radio burst with a spectral break, linking it to a shock crossing a streamer boundary, and proposes its use as a diagnostic tool for coronal density structures.

Contribution

It presents a detailed analysis of a type II radio burst with a spectral break, connecting it to shock-streamer interactions and suggesting its diagnostic potential.

Findings

Spectral break corresponds to shock crossing streamer boundary

Pre-break emission generated inside a streamer by a shock

Post-break spectrum indicates shock crossing into lower-density region

Abstract

We discuss an intriguing type II radio burst that occurred on 2011 March 27. The dynamic spectrum was featured by a sudden break at about 43 MHz on the well-observed harmonic branch. Before the break, the spectrum drifted gradually with a mean rate of about -0.05 MHz/s. Following the break, the spectrum jumped to lower frequencies. The post-break emission lasted for about three minutes. It consisted of an overall slow drift which appeared to have a few fast drift sub-bands. Simultaneous observations from the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) were also available and are examined for this event. We suggest that the slow-drift period before the break was generated inside a streamer by a coronal eruption driven shock, and the spectral break as well as the relatively wide spectrum after the break is a consequence of the shock crossing the streamer boundary where density drops abruptly. It is suggested that this type of radio bursts can be taken as a unique diagnostic tool for inferring the coronal density structure, as well as the radio emitting source region.