An Impulsive Flare Accompanied by a Cusp-Like Structure

V. Grechnev and H. Nakajima(Nobeyama Radio Observatory)

We report microwave and hard X-ray observations of an impulsive M2 class flare that occurred on 1999 September~17 at N13, W64. Since SXT images of this flare in the decay phase show that the flare region was rather complex and essentially composed of a bright loop and a cusp-like structure(possibly an arcade), we can learn whether electron acceleration was associated with the cusp-like structure or not.

Some of main results are as follows.

1. HXT images show a flaring loop and its footpoints.

2. Major emission at 34~GHz came from the whole hard X-ray loop(HXR loop), and from the region including and above it at 17~GHz.
3. There were two other weak sources at 17~GHz. One was located far from the 17~GHz major source and had a similar time profile to that of the major source with a small delay. The other was located near and above the 17~GHz major source, and emitted short-duration bursts that had almost no correlation with the major burst. Since it seems to be located below the cusp-like region, it probably had no relation to this structure.

These results suggest that high-energy electrons were not confined in the HXR loop, and their acceleration site was closely related to the HXR loop, but that they were not accelerated around the cusp region.