Koujun Yamashita

X-ray telescope onboard Astro-E: optical design and fabrication of thin foil mirrors

X-ray telescopes (XRTs) of nested thin foil mirrors are developed for Astro-E, the fifth Japanese x-ray astronomy satellite. Although the launch was not successful, the design concept, fabrication, and alignment procedure are summarized. The main purpose of the Astro-E XRT is to collect hard x rays up to 10 keV with high efficiency and to provide medium spatial resolution in limited weight and volume. Compared with the previous mission, Advanced Satellite for Cosmology and Astrophysics (ASCA), a slightly longer focal length of 4.5-4.75 m and a larger diameter of 40 cm yields an effective area of 1750 cm2 at 8 keV with five telescopes. The image quality is also improved to 2-arc min half-power diameter by introduction of a replication process. Platinum is used instead of gold for the reflectors of one of the five telescopes to enhance the high-energy response. The fabrication and alignment procedure is also summarized. Several methods for improvement are suggested for the reflight Astro-E II mission and for other future missions. Preflight calibration results will be described in a forthcoming second paper, and a detailed study of images will be presented in a third paper.

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 cm(2) 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 x 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.

Development and characterization of large x-ray mirrors for high-brilliance synchrotron radiation

Four kinds of large mirrors, which are 0.8 m SiC flat, 1 m SiC flat, and two 1 m Si cylindrical mirrors (coated with Pt or Ni), are developed for high brilliance synchrotron radiation with the cooperation of the suppliers. The reflectivity, surface finish, and surface figure are characterized by not only laser interferometers but also x-ray at ISAS 36 m long beamline.

Surface-roughness measurements of SiC x-ray mirrors

Our recent experimental and analytical results obtained so far for the surface roughness of the Pt-coated SiC flat mirrors are reviewed. Total reflectivity and angle resolved scattering (ARS) curves were measured using CuK(alpha) x ray for an 800 mm long mirror and three kinds of small mirrors having different surface roughness without heat load. The convolution analysis of ARS curves derived the power spectra of the surface waving of the mirror. The root mean square surface roughness calculated from the integral of the power spectrum is consistent with that estimated from the total reflectivity data. Also, the range of the surface wave number contributing the x-ray reflection was estimated and compared with that measured with the other types of experimental methods, heterodyne interferometer and scanning tunnel microscopy.