Design study of X-ray telescope onboard NeXT

Our previous balloon borne experiment, named InFOCμS, proved the imaging capability of the hard X-ray telescope in the energy band above 20 keV. The hard X-ray telescope onboard InFOCμS is the multi-nested thin foil optics using the platinum-carbon depth graded multilayers. Based on the experience of InFOCμS project, we are planing to develop the extremely broad-band X-ray telescope covering the energy range from 0.1 to 80 keV for the future Japanese X-ray astronomical satellite, NeXT (New X-ray Telescope), proposed to launch in 2010. We present here the scientific objectives for X-ray observations in that energy band and the investigation of the requirements for the NeXT X-ray telescope. In order to search the non-thermal emission from the rich clusters of galaxies with cluster-scale radio halo, the required effective area is at least 1000 cm² at 40 keV and the field of view should be larger than 10 arcmin × 10 arcmin. From the effective area estimated from the current design of multilayer parameters, it can be achieved with 4 telescopes with focal length of 12 m and diameter of 60 cm.