Microwave Spectra and Coronal Magnetic Structure of Flaring Active Regions

Abstract:

Microwave emissions during solar flares have a great sensitivity to magnetic field and can be used to diagnose magnetic field in the flaring regions. Ideally this diagnostic capability had better be applied to spatially resolved microwave spectra so that information of local magnetic field can be obtained. On the other hand it is also worthwhile to develop a diagnostic tool for spatially integrated microwave flux spectra, as are most commonly available to date. Our target is strong microwave bursts exhibiting significant fluxes at low (<5 GHz) frequencies which do not drop with decreasing frequency as much as a single uniform source would produce. We investigate the coronal magnetic structure of such microwave sources through a spectral modeling in which the volume and thickness of the microwave source are expressed as functions of magnetic field strength and the functions are adjusted to reproduce the spatially integrated spectra. It is found that the corona around the fan field lines in a separatrix dome structure is the most likely place to have the required spatial distribution of magnetic field strength and also to allow high energy electrons access. This spectral modeling uses, as constraints, hard X-ray spectra from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and microwave spectra from the Owens Valley Solar Array (OVSA) and the Korean Solar Radio Burst Locator (KSRBL).