Radio imaging of shock-accelerated electrons associated with an erupting plasmoid on 2010 November 3

We present observations of a metric type II solar radio burst that occurred on the 3rd of November 2010 in association with an erupting plasmoid. The eruption was well observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and the Reuven Ramaty High Energy Solar Spectroscopic Imager, while the burst occurred in the frequency range of the Nançay Radioheliograph (NRH). Such events, where the type II emission occurs in the NRH frequency range, allowing us to image the burst, are infrequent. Combining these data sets, we find that the type II is located ahead of the hot (11MK) core of the plasmoid, which is surrounded by a well-defined envelope of cool (fewMK) plasma. Using two methods, we determine the propagation velocity of the shock: (1) fitting the type II emission observed in PHOENIX and HUMAIN radio spectrogram data; (2) direct imaging of the type II source location using NRH observations. We use LASCO C2 polarized brightness images to normalize our coronal density model. However, we find that information from imaging is required in order to fine-tune this normalization. We determine a shock propagation velocity between 1900 km s^-1 and 2000 km s ^-1. This is faster than the plasmoid observed at extreme-ultraviolet wavelengths by AIA (v = 670-1440 km s^-1, where the cooler plasma propagates faster than the hot core). The positioning of the type II, ahead of the plasmoid, suggests that the electrons are accelerated in a piston-driven shock.