X–ray telescope onboard astro–E. II. Ground–based x–ray characterization

X-ray characterization measurements of the x-ray telescope (XRT) onboard the Astro–E satellite were carried out at the Institute of Space and Astronautical Science (Japan) x–ray beam facility by means of a raster scan with a narrow x–ray pencil beam. The on–axis half–power diameter (HPD) was evaluated to be 1.8’–2.2’, irrespective of the x–ray energy. The on–axis effective areas of the XRTs for x–ray imaging spectrometers (XISs) were approximately 440, 320, 240, and 170 cm² at energies of 1.49, 4.51, 8.04, and 9.44 keV, respectively. Those of the x–ray spectrometer (XRS) were larger by 5–10%. The replication method introduced for reflector production significantly improved the imaging capability of the Advanced Satellite for Cosmology and Astrophyics (ASCA) XRT, whose HPD is -3.6’. The increase in the effective area by a factor of 1.5–2.5, depending upon the x–ray energy, compared with that of the ASCA, was brought about by mechanical scale up and longer focal lengths. The off–axis HPDs were almost the same as those obtained on the optical axis. The field of view is defined as the off–axis angle at which the effective area becomes half of the on–axis value. The diameter of the field of view was - 19’ at 1.49 keV, decreasing with increasing x–ray energy, and became -13’ at 9.44 keV. The intensity of stray light and the distribution of this kind of light on the focal plane were measured at the large off–axis angles 30’ and 60’. In the entire XIS field of view (25.4 mm × 25.4 mm), the intensity of the stray light caused by a pointlike x–ray source became at most 1% of the same pointlike source that was on the optical axis.