A coronal transient associated with a high-speed type II burst

Abstract

Several characteristics of a white light transient observed by the ATM Coronagraph experiment aboard Skylab are discussed. The transient was associated with a very high speed type II radio burst. The observed plane of the sky speed of the burst was 4900 km/s, 6-7 times higher than the speed of the transient itself. Based on the relative speeds of the transient and the radio burst, it is argued that the type II disturbance must have propagated in a still undisturbed corona, at an approximately 35-deg angle to the preexisting streamer and along an essentially open field configuration. The electron density gradients derived from the radio and the white light observations are compared, and it is shown that they are in agreement within the limits of the observations. The assumption that the type II was a weak MHD shock leads to large values for the coronal magnetic field. The possibility that the type II radition originated in a strong shock, with a magnetic Mach number greater than 2, is considered.