We have been developing a hard X-ray imaging telescope with Pt/C multilayers for balloon experiments and
for ASTRO-H. Calibration of the hard X-ray telescope has been performed at the synchrotron radiation facility,
SPring-8, to obtain point spread function and effective area for the InFOCuS and SUMIT experiments. Hard
X-ray characterization at the SPring-8 beamline BL20B2 has great advantages over those with conventional
sources, such as an extremely high flux, a larger beam with less divergence, and a selectable, narrow bandwidth
covering the hard X-ray region from 20 to over 100 keV. We have been successful not only in characterizing the
telescope but also in establishing the tuning procedure to improve its image quality. The 16m-long experimental
hutch has sufficient capability for characterization of the telescope with a long focal length up to 12 m as well
as reflectivity and diffraction measurements of multilayer reflectors. Recently we have measured 87 pairs of
multilayer mirrors and obtained an angular resolution of 1.5 arcmin (HPD), and reflectivity of Pt/C multilayers
designed for ASTRO-H. In this paper, we report recent results of X-ray measurements of our hard X-ray telescope
and multilayer mirrors.
We present a plan for calibration of the NeXT hard X-ray telescopes (HXT) at the synchrotron radiation facility, SPring-8. In hard X-rays, it is difficult for a laboratory-based beamline using a conventional X-ray source to provide sufficient capabilities for pre-flight high-precision calibration. Therefore, we plan to characterize the NeXT HXT at the SPring-8 beamline BL20B2. SPring-8 is one of the world's third-generation synchrotron radiation facilities. Measurements at BL20B2 have great advantages over those done with conventional sources, such as an extremely high flux, a larger beam with less divergence, and a selectable, narrow bandwidth covering the hard X-ray region from 8 to over 100 keV. The 16m-long experimental hutch has sufficient capability for characterization of the NeXT HXT (FL=12m). In the past, we have measured the Point Spread Function (PSF) and effective area of telescopes for balloon-borne hard X-ray imaging experiments (e.g. InFOCuS, SUMIT) at several energies from 20 to 60 keV. Furthermore, we have successfully established a tuning procedure to improve their image quality. We plan to measure the X-ray characteristics (PSF, effective area, stray light, and so on) of the NeXT HXT to build up the HXT response function.
Hard X-ray telescopes using depth-graded multilayer is a key technology for future satellite programs. Developments
are underway by many groups, and balloon experiments have also been carried out. We have developed
light-weight hard X-ray telescopes using Pt/C multilayer and high-throughput thin-foil optics. They have been
aboard on InFOCμs and SUMIT balloon flights. As a next development efforts, especially for Japan's NeXT
satellite program, we focus on improvement of image quality. Among three equally-contributing error factors
(figure error, positioning error and off-roundness), figure errors and off-roundness have been reduced significantly, by screening of replication mandrels and active and iterative tuning of support bars. Further studies are
in progress, such as suer-polished metal mandrels and better positioning of reflector edges, to meet the baseline
requirement of the NeXT mission.
Imaging observations by means of optics is crucially important, not only for its capability of spatially resolving
astronomical objects, but also for its sensitivity superior to non-imaging experiments by orders of magnitude.
In order to study feasibilities of reflective optics in soft gamma-ray region, we measured Pt/C multilayer and
multilayer-supermirror at 200 keV. Angular dispersion is measured at wide range of incidence angle. The results
showed that measured reflectivities agree well with model calculation using tabulated optical constants and
roughness measured at 8.4, 30 and 60 keV. Possible configuration of soft gamma-ray telescope is discussed.
Imaging observation in the hard X-ray band of 10 - 100 keV is one of the important subjects in X-ray astronomy.
Though SUMIT balloon-borne experiment, we have developed thin-foil-nested hard X-ray telescope employing
depth-graded Pt/C multilayer (multilayer-supermirror). We have improved production process of the replica
reflector and telescope optics compared with InFOCμS-2004 telescope. The new telescope was measured at
synchrotron radiation facility, SPring-8. The image quality and throughtput were estimated to be 2.06 arcmin
(half power diameter) and 85 % at 30 keV, respectively. These values were about 24 % and 30 % improvement
compared to InFOCμS-2004, respectively. Limiting factors of its performance are also investigated. Based on
such an investigation we are now continuously developing hard X-ray telescope for SUMIT 2006 flight.
The relevance of pre-flight calibration of space-born instruments is widely recognized. As an energy region of interest shifts to hard X-rays in these years, measurement setup becomes difficult to be afforded or maintained by a laboratory- or small-collaboration-based resources. In 10 to 100 KeV region X-ray source that is bright and monochromatic enough to calibrate optics in detail is no longer available other than at synchrotron facilities. Focal length becomes longer and this is another aspect that is beyond capabilities of soft-X-ray-oriented facilities. The hard X-ray instruments for balloon program have been characterized at synchrotron facility SPring-8/BL20B2 in Japan. SPring-8 is one of the world's brightest third generation synchrotron radiation facilities. BL20B2 is specialized for medical and imaging experiment, and has 200m-long transport tube. Measurement at BL20B2 has great advantages such as extremely high flux, large sized and less divergent beam, and monochromatic beam covering entire hard X-ray region from 8 to 12keV. 16m-long experiment hutch is capable of long focal length of hard-X-ray telescope. Pt/C multilayer-supermirror hard X-ray telescopes, position-sensitive scintillation counter and scintillator-deposited CCD, have been characterized at the facility. Insttrumentation of the facility and some of measurement results are presented.