Hard X-ray imaging of the solar flare on 1981 May 13 with the HINOTORI spacecraft

Abstract

Hard X-ray images and X-ray spectra of an intense solar flare that occurred at E58N09 on 1981 May 13 are presented and discussed. The observation was made with Japanese solar X-ray spacecraft Hinotori. An unusual hard X-ray source, observed at 14-38 keV, had a steady spatial displacement of approx.1' toward the limb from the two-ribbon H..cap alpha.. flare during the 16 minutes of hard X-ray observation, including the time of maximum flux. This suggests that the source was located near the top of a coronal loop structure connecting the two ribbons, at an estimated altitude of approx.4 x 10/sup 4/ km above the photosphere. The soft X-ray (5-10 keV) source nearly coincided in position and size with the hard X-ray source. Near the peak of hard X-ray time profile, approx.40% of the total count rate of the har X-ray image is estimated to come from a power-law component, as observed with the hard X-ray spectrometer. The parameters of the thermal plasma near the loop top were determined to be eta = 3 x 10/sup 10/ cm/sup -3/, T = 2 x 10/sup 7/ K, and ..beta.. = 16..pi..etakT/B/sup 2/roughly-equal1.0. Intense heat conduction from the thermal plasma near the loop topmore » to the transition region appears to be equilibrium with the continuous energy release near the loop top.« less