High-Altitude HXR source in the 23 Apr. 1998 Flare





We analyzed the loop-top source of an X 1.2 flare, which occurred on 1998 April 23, based on the hard X-ray and the microwave data. This flare occurred slightly behind the solar limb. Therefore, the footpoint emission, which is normally dominant, was blocked and only the source located at the loop-top region is well observed. The hard X-ray emission from the loop-top source is revealed to come from both the nonthermal electrons and the thermal plasma. The power-law index of the nonthermal electrons observed in hard X-rays is about 2.9 on the assumption of the thin-target model. This is consistent with the index of 2.5 - 3 derived from the dual-frequency observation in microwaves. This is the evidence that the nonthermal high-energy electrons exist in the loop-top region.



On the other hand, the temperature of the thermal plasma is derived to be about 33 MK. The thermal and non-thermal components show complicated spatial structure each other, and source position of the non-thermal component does not show a good correspondence to that of the thermal component.



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