(Kosugi et al., Publ. Astron. Soc. Japan, 44, L45-L49, 1992.)
Yohkoh/HXT observes solar flares in four energy bands (14 - 23 - 33 - 53 - 93 keV). In the higher energy bands (above 33 keV), HXT observes almost pure non-thermal emission from footpoints of a flaring loop. In the lowest energy band (14-23 keV), thermal emission from a super-hot (T > 30 MK) plasma becomes dominant, especially in the gradual phase. This thermal emission are usually observed around the apex of a flaring loop. Since both components are observed in the energy range of 23 - 33 keV, a hard X-ray image in this energy range, sometimes shows a complex structure.
An X-class flare was observed with HXT on board Yohkoh on 3 December 1992. These images are synthesized by the Maximum Entropy Method (MEM) from the photon-count data taken simultaneously in the four energy bands near the time of peak flux after two seconds of integration with the background subtracted. The field of each map is 39".5 x 39".5, with the top towards the north pole of the Sun and the left towards the east. This flare occurred near the east limb at N17 E72.