We study the non-thermal emissions in a solar flare occurring on 2003 May 29 by using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This flare shows several typical behaviors of the HXR and microwave emissions: time delay of microwave peaks relative to HXR peaks, loop-top microwave and footpoint HXR sources, and a harder electron energy distribution inferred from the microwave spectrum than from the HXR spectrum. In addition, we found that the time profile of the spectral index of the higher-energy (gsim 100 keV) HXRs is similar to that of the microwaves, and is delayed from that of the lower-energy (lsim 100 keV) HXRs. We interpret these observations in terms of an electron transport model called trap-plus-precipitation. We numerically solved the spatially-homogeneous Fokker-Planck equation to determine electron evolution in energy and pitch-angle space. By comparing the behaviors of the HXR and microwave emissions predicted by the model with the observations, we discuss the pitch-angle distribution of the electrons injected into the flare site. We found that the observed spectral variations can qualitatively be explained if the injected electrons have a pitch-angle distribution concentrated perpendicular to the magnetic field lines rather than isotropic distribution.
Authors: T. Minoshima, T. Yokoyama, and N. Mitani
Publication Status: ApJ (accepted)
Last Modified: 2007-10-03 07:45