Direction-finding Analysis of the 2012 July 6 Type II Solar Radio Burst at Low Frequencies

Abstract

The 2012 July 6 X1.1 flare at S13W59 and a halo coronal mass ejection (CME) with a space speed of ∼1900 km s^-1 were associated with type III and type II radio bursts. The metric-to-decametric type II radio burst extended down to ∼5 MHz. Simultaneously, a slowly drifting feature with a harmonic structure was observed by Wind and Solar Terrestrial Relations Observatory radio receivers around and below 1 MHz, above the strong type III radio burst at lower frequencies. The radio direction-finding analysis of this lower-frequency interplanetary (IP) type II radio burst indicates that the radio source was located near the nose and possibly toward the southern flank of the CME-driven shock. These results provide an independent confirmation of the previous suggestions that when the metric and IP type II bursts are overlapping, the lower-frequency IP type II radio burst originates near the shock nose, whereas the source of the higher-frequency metric type II burst is closer to the Sun in the shock flank region. These results further support the idea that the coronal and IP type II bursts are produced by the same CME-driven shock.