Detailed measurements of reflectivity of gold, which is used for X-ray mirror for X-ray telescope onboard "Suzaku"
satellite was performed in the synchrotron radiation facility SPring-8 BL15XU. We measured reflectivity of the
mirror, which uses total reflection of gold thin layer. Grazing incidence angle is 0.5 degree and incident X-ray
monochromatized in the energy range from 2.2 keV to 3.5 keV, where M-edge structure of gold appears. We used
double crystal monochrometer using Si(111) crystal, (ΔE/E ~ 10-4) to monochromatize the incident X-ray.
Energy calibration was performed using L-edge of molybdenum (2530.2 eV) and K-edge of argon (3205.9 eV).
From the results, that the energy of M-V and M-IV edge of gold is different from optical constant table, and
almost same as the value reported by Graessle et al.(1992).1 It is important to study the optical constants of
gold or other mirror material for X-ray astronomy.
This results will be feed back to the response function of the X-ray telescope of Suzaku satellite. It is very
important for X-ray spectroscopy in X-ray astronomy.
We present X-ray characteristics of X-ray telescopes (XRTs) onboard the Astro-E2 satellite. It is scheduled to be launched in February 2005. We have been performed X-ray characterization measurements of XRTs at Institute of Space and Astronautical Science (ISAS) since January 2003. We adopted a raster scan method with a narrow X-ray pencil beam. Angular resolution of the Quadrants composed of the Astro-E2 XRT was evaluated to be 1'.6-2'.2 (HPD; Half Power Diameter), irrespective of the X-ray energy, while those of the Astro-E XRT was 2'.0-2'.2. The effective area of a telescope is approximately 450, 330, 250, and 170 [cm2] at energies of 1.49, 4.51, 8.04, and 9.44 keV, respectively. The field of view (FOV) of the XRTs which is defined as Full Width Half Maximum (FWHM) of the vignetting function is ≈18' at 4.51 keV. We summarize these characters of the XRTs.
We report a ground-based X-ray calibration of the Astro-E2 X-ray
telescope at the PANTER test facility. Astro-E2, to be launched in
February 2005, has five X-Ray Telescopes (XRTs). Four of them focus on
the X-Ray Imaging Spectrometers (XIS) while the other on the X-Ray
Spectrometer (XRS). They are designed with a conical approximation of
Wolter-I type optics, nested with thin foil mirrors to enhance their
throughput. A calibration test of the first Astro-E2 flight XRT for
XIS was carried out at the PANTER facility in August 2003. This
facility has an 130 meter long diverging beam from X-ray generator to
XRT. Owing to the small X-ray spot size of about 2 mm dia., we verified that the focal position of each quadrant unit converged within 10 arcsec. The energy band around Au-M edge structures was
scanned with a graphite crystal. The edge energy (Au M5) is consistent with that listed in Henke et al. 1997. Owing to the large area coverage of the PSPC detector which is a spare of the ROSAT satellite, off-axis images including stray lights at large off-axis angle (up to 6 degree) were obtained with a large field of view. We also compared the results with those measured with the parallel pencil beam at ISAS which is in detail reported in our companion paper by Itoh A. et al..
Astro-E2 XRTs adopt Wolter Type-I optics and have nested thin foil structure to enhance their throughput. But this structure allows stray X-rays to come from the sky outside of the XRT field of view. Stray lights contaminate focal plane images, especially in the case of extended source observations. We intend to mount pre-collimators on top of the ASTRO-E2 XRTs to intercept stray lights. According to the success for the engineering model pre-collimator to protect the stray lights efficiently, we proceeded to product flight model pre-collimators. Some improements are made for the flight model (FM) pre-collimator: the introduction of heat forming to make slats accurate cylindrical shape, the change of the groove shape of alignment plates and the change of the housing design. We also established the method of pre-collimator mounting. In X-ray measurements, stray light images and the flux of each stray component at any off-axis angles are measured with/without FM pre-collimator. The secondary only reflection component is reduced down to 3% at a larger off-axis angle than 30', and the backside reflection component becomes more remarkable. On the other hand, X-ray measurement of the effective area at on-axis with/without FM pre-collimator verifies that pre-collimator does not interfere the telescope aperture. In addition, the decrease of XRT field of view is ≤8%, which is the same as the ray-tracing simulations.
Astro-E2, to be launched in early 2005, will carry five X-ray Telescopes (XRT). The design of the XRT is the same as the previous original mission Astro-E, that is a conical approximation of Wolter Type-I optics, where about 170 thin-foil reflectors are nested confocally. Some modifications from Astro-E are adopted within the severe constraints due to the policy of "re-build" instruments. One of the major changes is the addition of pre-collimators for the stray light protection. Several modifications on the fabrication processes are also made. The replication glass mandrels are screened carefully, which is expected to reduce the figure error of replicated reflectors. We thus expect better performance than Astro-E especially in imaging capability. In order to qualify the performance of the Astro-E2 XRT, we have started ground calibration program of XRT at 30 meter X-ray beam facility of the Institute of Space and Astronautical Science (ISAS). We have found positive improvements on the telescope performance from the Astro-E, which probably arise from the applied modifications. The on-axis half-power diameter (HPD) has been evaluated to be 1.6-1.7 arcmin, which is improved from the Astro-E (2.0 ~ 2.1 arcmin HPD). The on-axis effective areas of quadrants are larger than the average of Astro-E by about 5%. The on-axis effective areas of the XRT for X-ray Imaging Spectrometers (XIS) are approximately 460, 340, 260, and 190 cm2 at energies of 1.49, 4.51, 8.04, and 9.44 keV, respectively. The present paper describes the recent results of
the performance of the first flight assembly of the Astro-E2 XRT.
We report a new calibration system for large size X-ray optics at
ISAS. We adapted a 'dynamical' pencil beam collimated from an X-ray
generator, the maximum voltage for which is 50 kV. By combining two
stage systems for the X-ray generator and a collimator, the pencil
beam dynamically sweeps across a circular region of a telescope with
the radius of 60 cm at maximum. In this case, the X-ray telescope and
the focal plane detector are both statically fixed. A 4.4~m long rail
for detector stage and two positions of the telescope stage provide
focal lengths from 4.5 to 12 m, while the previous system can
accommodate 4.5 or 4.75 m focal length. The preliminary performance of
this system is summarized in this paper. For the post-Astro-EII
satellite, a hard X-ray multi-layer supermirror with an unprecedented
sensitivity up to 80~keV is strongly expected. This beam facility is of importance because the hard X-ray mirrors always require a long focal length of 8-12 m due to the small reflection angle (about 0.3 degree). Focal length and diameter of future telescopes are always decided by the boundary conditions of the mission at the last moment of the design freeze. Our new X-ray beam facility is designed to match with any kind of X-ray telescope parameters.