Cryogenic imaging spectrometers for X-ray astronomy

During 1999 and 2000 three X-ray astronomy satellite missions will be launched. One of those, the Japanese ASTRO-E, carries the first cryogenic X-ray imaging spectrometer with an energy resolution of approximately 10 eV in the range 0.5–7 keV and with 2×18 pixels. Ambitious plans do exist for future X-ray spectroscopy missions like Constellation-X at NASA and the X-ray Evolving Universe Spectrometer at ESA. To meet their science objectives these missions rely heavily on cryogenic imaging spectrometers with at least 32×32 imaging elements and a spectral resolution of 2–5 eV in the 0.5–10 keV energy range. This paper shortly addresses the principles of superconductive tunnel junction spectrometers and microcalorimeters and reviews the present status with regard to energy resolution, detection efficiency, count rate ability and imaging prospects.