Microwave and Hard X-Ray Spectral Evolution for the 13 December 2006 Solar Flare

Abstract

This paper explores the time evolution of microwave and hard X-ray spectral indexes in the solar flare observed by Nobeyama Radio Polarimeters (NoRP) and the Ramaty High Energy Solar Spectroscopy Imager (RHESSI) on 13 December 2006. The microwave spectral index, gamma (MW), is derived from the emissions at two frequencies, 17 and 35 GHz, and hard X-ray spectral index, gamma (HXR), is derived from RHESSI spectra. Fifteen subpeaks are detected at the microwave and hard X-ray emissions. The microwave spectral indexes tend to be harder than hard X-ray spectral indexes during the flare, which is consistent with previous findings. All detected subpeaks follow the soft-hard-soft spectral behaviours in the hard X-ray rise-peak-decay phases. However, the corresponding microwave subpeaks display different spectral behaviour, such as soft-hard-soft, soft-hard-harder, soft-hard-soft+hard or irregular patterns. These contradictions reveal the complicated acceleration mechanism for low- and high-energy electrons during this event. It is also interesting that the microwave interpeak spectral indexes are much more consistent with one another.