Observation of solar flare hard X-ray spectra using CdTe detectors Original Research Article

We present the design and initial flight results of a balloon-borne hard X-ray spectrometer for observing solar flares. The instrument is designed for quantitative observation of nonthermal and thermal components of solar flare hard X-ray emission, and has an energy range of 15–120 keV and an energy resolution of 3 keV. The instrument is a small (gondola weight 70 kg) system equipped with sixteen 10 × 10 × 0.5 mm CdTe detectors, and designed for a 1-day flight at 41 km altitude. Detector temperature of −15 °C was achieved through radiative cooling alone. Pre-flight tests confirmed that all detectors exceeded the target 3 keV resolution. No flares were observed during the 2001 flight, but the second flight on May 24, 2002 succeeded in observing a class M1.1 flare. Preliminary analysis indicates the observed spectrum is consistent with a purely thermal plasma at an unusually high temperature of 47 mK.