Options for an imaging array of micro-calorimeters for X-ray astronomy

A feasibility study of an imaging 32×32 pixel micro-calorimeter array, intended for the XEUS mission is presented. Three different concepts, theoretically leading to an imaging spectrometer that combines an energy resolution of 5 ev for 8 keV X-rays and a count rate of at least 100 counts/s/pixel, are presented and discussed. Current progress in the field of single-pixel micro-calorimeters employing voltage-biased transition edge sensors forms the basis for the selection of this type of device. The design concepts originate from different philosophies for the thermal design and geometrical lay-out and will use state of the art micro-machining and lithography. SQUID read-out will be the challenge and grouping of pixels might be considered, both from an electrical and a cooling point of view.