Study of the early phase of a Coronal Mass Ejection driven shock in EUV images

Abstract

The November 1st, 2014 prominence eruption (associated with a C2.7 class flare) resulted in a fast, partial-halo Coronal Mass Ejection (CME). During its early propagation, the CME produced a type II radio burst (seen by the Bruny Island Radio Spectrometer) starting around 04:57 UT when the front entered into the LASCO/C2 field of view (FOV) and the top of the CME front was at the heliocentric distance of about 2.5 $R_{\odot}$. In order to identify the source of the type II radio burst, we studied the kinematic of the eruption with EUV images acquired by SDO/AIA. Profiles of the observed EUV front speed have been compared with the Alfvén speed profiles derived by combining the plasma electron densities obtained from Emission Measure analysis and model magnetic fields extrapolated on the plane of the sky. Our results show that the northern half of the front became super-Alfvénic at approximately the same time when the type-II radio burst started. A comparison between the starting frequency of the type II emission and the frequencies corresponding to the coronal densities of the locations where the EUV front became super-Alfvénic suggests that the radio sources should be located in the northern flank of the front.