The Development of DIOS FXT (Four Stage X-ray Telescope)

A small satellite mission DIOS (Diffuse Intergalactic Oxygen Surveyor ) is planned to observe the warm-hot intergalactic medium ( WHIM ) of a few millions of degree, by mapping the redshifted emission lines of oxygen. FXT( Four Stage X-ray Telescope) has been developed as the best fit optics for DIOS. The X-ray measurement of the first demonstration model showed a few time larger angular resolution than designed value and compact optical measurement systems for each stage single mirror were made to clarify the reason of worse performance. We will report on the present status of the development of FXT including compact optical measurement system and reexamination of the process of replica foil mirror fabrication.