Hard X-ray observation of solar flares with balloon-borne CdTe spectrometer

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The purpose of the research is to develop the balloon-borne Cadmium telluride detector spectrometer, and to observe solar flare hard X-rays during the current solar maximum. The development of the spectrometer with 16 detections was completed in the summer of 2001, and the ISAS balloon B80-6 was launched in 2001 October 29 from the Sanriku Balloon Center of ISAS, and the observation at 42 km altitude was successfully carried out. Though solar flares were unfortunately not detected, the instrument worked fine, and high-quality background data was taken. The detector was cooled down to -10 degree C, and the spectral resolution was 2,503 KeV, which was quite good as compared with conventional detectors. The instrument was recovered in the Japan sea. Following the successful demonstration of the instrument performance, the second flight experiment was done in 2002 May 24. An M1.2 flare was detected at 15:30 JST. We believe that this is the first detection of hard X-rays from celestial sources with the CdTe detectors. 16 detectors worked fine throughout the observation, and the emission lines from the shield lead allow us to confirm that there was no degradation in energy gain and resolution. The initial portion of the flare was also observbed with NASA RHESS satellite,which carried germanium detector and modulation collimator, and both results coincided very well. An initial analysis showed that the observed spectra were well fitted by 50 MK thermal spectra, and detailed study is going on with radio data taken with the Nobeyama radio heliograph.