Type II spectral bumps and Diagnostics on the Properties of the Radio Source

It is now widely accepted that type II radio bursts are due to energetic electrons accelerated at coronal shocks. Radio observations, however, have poor or no spatial resolution to pinpoint the exact acceleration locations of these electrons. In this presentation we propose a novel method to infer the source properties of type II radio bursts by combining radio and white light observations. The key assumption is to relate specific morphological features (e.g., spectral bumps) of the dynamic spectra of type II radio bursts to imaging features (e.g., CME and its driven shock entering into a streamer) along the CME propagation. To verify the above proposal, we investigate two type IIs with spectral bump features and examine their association with CME-streamer interactions. The features are interpreted as a natural result of the shock-radio-emitting region entering the dense streamer structure. It is inferred that the type II radio bursts are excited at the flanks of the CME-driven shock (where the large scale shock geometry is of quasi-perpendicular), and the radio emission is spatially confined to a very localized region.