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Session 85 - Instruments, Databases and Techniques.
Oral session, Thursday, June 13
We present observations of a flare that occured on 1995 Oct 11, in AR 7912 obtained with the frequency-agile solar interferometer at Owens Valley Radio Observatory (OVRO) made with both high spatial and spectral resolution. We analyzed data at 32 frequencies in the range 1.2-12.4 GHz for both left-handed and right-handed circular polarizations applying the recently completed Spatial/Spectral Maximum Entropy Method (MEM). In contrast to the traditional MEM algorithm, which does not exploit the spatial information available at adjacent frequencies in the OVRO data, the new algorithm obtains a global solution to the visibilities in both the spatial and spectral domains and leads to spectra which are greatly improved in smoothness and dynamic range. A comparison with BBSO data shows that the optical flare is associated with the trailing sunspot of the active region, while the leading sunspot shows no flare related brightning. The reconstructed radio images show two sources; one of them, the primary source, is associated with the optical flare and has its peak emission at about 7.0 GHz, while the other one, the secondary source, is associated with the leading sunspot with a peak emission at about 2.8 GHz. The slopes of the brightness temperature spectra imply that in both cases non-thermal gyrosynchrotron emission is the process responsible for the microwave radiation. A preliminary model fit of the spectra shows that the emission of both sources comes from low-order harmonics and that the estimated magnetic field strength and the estimated density of nonthermal electrons of the primary source are much larger than the corresponding values of the secondary source. The results suggest that the two sources are connected by a large secondary loop and that the emission of the secondary source is caused by nonthermal electrons escaping from the primary source. The time evolution of the two sources within about \pm 3 min of the flux peak time can be described by an increase in the number of nonthermal electrons up to the peak time and by a subsequent decrease.
Program listing for Thursday