Magnetic structure of a flaring region producing impulsive microwave and hard x-ray bursts

We have synthesized 6 cm ''snapshot'' maps from VLA observations of the 1B/M1 flare of 1980 June 25. The spatial and temporal resolutions during the 9 minutes of the impulsive phase were 1'' x 2'' and 10 s, respectively. There appears to be some displacement between the locations of the burst source and the preflare loop structures seen in the preflare map. The burst peak occurred on the neutral line of the preflare polarization map, between the two oppositely polarized microwave ''loop'' structures about 40'' long. Concurrent hard x-ray observations were made of the burst, but these had no spatial resolution. The 6 cm maps show the locations of several of the x-ray burst spikes. The 6 cm burst was fully resolved into at least eight components, many of which were bipolar in nature. The four strongest components form a magnetic arcade which bridged the photospheric magnetic neutral line, and the Hα flare ribbons appear as ''footprints'' to these magnetic structures. The 6 cm emitting region occupies a large fraction of the flaring loops including their tops. During the course of the impulsive phase, the sources drift limbward several arcsec, suggesting ascension or progressive bursting at higher levels, much like the ascension of x-ray loops observed during the thermal phase of flares