Thermal detectors for X-ray astronomy

The characteristics of an 'ideal' spectrometer for X-ray astronomy are discussed. Special attention is given to the development of new thermal detectors (calorimeters) for the AXAF, which are based on the conversion of the energy of a single X-ray photon entirely into heat. The results obtained so far yielded the FWHM value of 17 eV at 100 mK, but the values for each of the contributing noise components measured separately were less than 10 eV, suggesting that the limiting value for AXAF will be better than 10 eV. A summary of the expected parameters for an AXAF calorimeter is presented.