Establishing the response function of the x-ray telescopes onboard the Suzaku satellite

Suzaku, the fifth in a series of Japanese X-ray astronomy satellites following the highly successful Hakucho, Tenma, Ginga and ASCA satellites, was launched on July 10th, 2005. The X-ray telescope (XRT-I0 through I3) together with the focal plane detector XIS (XIS 0 through 3 corresponding with the number of XRT-I) has features of low background and large effective area covering an energy range from 0.2 to 12 keV. The XRTs were manufactured mostly by a hand, so that their response function is well known very complex. In order to improve the accuracy of the function, we have been developing a Monte-Carlo technique that simulates the X-ray event reflected at the XRT with one photon by one photon (ray-tracing). The imaging capability, the point spread function (PSF) or the encircled energy function (EEF), is the most complex in the response function, that varies from telescope to telescope and ranges from 1.′8 to 2.′3 in half power diameters (HPD). We found that their variations are primarily due to the difference of their focal length. We then tuned the focal length and found that the PSF or EEF was better reproduced when the variations of -50 −+50 mm are given to the focal length of 4750 mm.