2012/03/07 by Xiang-Liang Kong, Yao Chen, Gang Li +4 · 1 citation
Physics and Astronomy · #astro-ph.SR #physics.space-ph
paper · pdf · doi:10.1088/0004-637x/750/2/158
12 pages, 5 figures, accepted by ApJ 2012
arxiv created 2012/03/07 · arxiv updated 2015/06/04
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.