XRT Mirrors

The ROSAT XRT consists of four nested co-focal Wolter type 1 gold-coated Zerodur (glass) grazing incidence mirrors manufactured by Zeiss in Germany. The system has a field of view larger than the 2^o diameter of the PSPC (the HRI is smaller), although vignetting is significant at large off-axis angles, especially at high energies. The mirror system has a focal length of 240cm, a focal plane scale of 11.64 $\mu$ per arcsecond, and a geometric area of 1141 cm². The point spread function and effective area is described in the sections on the PSPC and HRI detectors.