Two-frequency imaging of microwave impulsive flares near the solar limb

Using the VLA, we observed two impulsive microwave and hard X-ray flares that occurred close to the solar limb on 1981 November 21 and 22. Images were obtained simultaneously at 4.9 and 15 GHz every 10 s during the 5 minute durations of the flares. Even though the radio and hard X-ray time histories indicated that they were simple impulsive flares, the VLA observed no 4.9 GHz radiation at all from one flare. From the other, the 15 GHz radiation emanated from a smaller source at a lower altitude and a different position angle than did the 4.9 GHz radiation; furthermore, the degree and sense of circular polarization differed in the two sources, and both showed complicated variations with time