Improvement of Yohkoh HXT imaging and an analysis of the 1997 November 6, X9 flare Original Research Article

The imaging capability of the Hard X-ray Telescope (HXT) on board Yohkoh has been drastically improved by (1) adopting new instrumental response functions (modulation patterns) derived from a self-calibration procedure that makes use of solar flares themselves as calibration sources, (2) revising the Maximum Entropy (MEM) image synthesis procedure for better total flux estimation, and (3) incorporating in MEM properly estimated observation errors. One of the most intense flares so far observed with HXT, the 1997 November 6, X9 flare, has been analyzed with the new HXT imaging program. Two footpoint sources are clearly seen and show systematic motions during the impulsive phase. This may provide a new clue to understand the coronal magnetic field structure involved in the energy release process of flares.