K.-i. Tamura

Soft x-ray calibration for the NeXT x-ray telescope

We present a plan on soft X-ray calibration for the New Exploration X-ray Telescope (NeXT). Two hard and two soft X-ray telescopes (HXTs/SXTs: see Ogasaka et al. 2008 in this volume) provide images up to 80 keV with a large effective area. Following to the Suzaku X-ray telescope, the mirrors on SXTs are tightly nested to maximize the aperture efficiency. To illuminate the mirrors at all, we plan to adopt a raster scan system using a pencil beam collimated from an X-ray generator. We summarize a current status of the soft X-ray ground calibration system at ISAS/JAXA. We also review the calibration of the Suzaku XRTs since the optics are very similar to the NeXT SXTs.

The hard X-ray polarimeter X-Calibur

X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as binary black hole systems, micro-quasars, active galactic nuclei, and gamma-ray bursts. We designed, built and tested a hard X-ray polarimeter, X-Calibur, to be used in the focal plane of the In FOCμS grazing incidence hard X-ray telescope. X-Calibur combines a low-Z Compton scatterer with a CZT detector assembly to measure the polarization of 20-60keV X-rays making use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation; in principal, a similar space-borne experiment could be operated in the 5-100keV regime. X-Calibur achieves a high detection efficiency of order unity.

New multilayer design for ASTRO-H/hard x-ray telescope and missions beyond

Japans sixth X-ray satellite missions, ASTRO-H, features two hard X-ray telescopes with depth-graded, multilayer reflectors. Our laboratory has advanced the technology for multilayer reflectors through development of a balloon-borne experiment, InFOCuS. While its base model for the multilayer design (with the minimum incident angle of 0.11 degrees and 8m focal length) is adequate for the ASTRO-H mission, we opt to improve it further so that better performance can be derived with the minimum incident angle of 0.07 degrees and 12m focal length. The improved design has resulted in the reduction of layers from 28 to 10-21 layers per reflector while gaining higher reflectivity by 3-5% at 40-70 keV. A multilayer optics will be used in ATHENA. ATHENAs principal design requires its energy bandpass of 0.1-20 keV with the minimum incident angle of 0.31 degrees and 12m focal length. With the narrower bandpass and the larger incident angles, it necessitates following changes in the multilayer design: adjustment of top Pt layer thickness and a total number of top layers to boost reflectivity (especially in the lower energy band), and refinement of Pt/C-layer spacing and depth-graded period below the third layer to bunch up the Bragg peaks tightly in the required hard X-ray band. In this presentation, we discuss the key parameters for ATHENAs multilayers to achieve a larger effective area at 10-20 keV.

Design study of telescope housing for the NeXT/XRT

We present a study on housing design for the X-ray telescopes (XRT) onboard the New Exploration X-ray Telescope (NeXT). The NeXT XRTs are larger than previous thin-foil XRTs. The XRT is required to have a sufficient stiffness in order to keep the high performance of the XRT in orbit. We performed a structure analysis of the virtual model of the NeXT XRT housing using the FEA software Marc. A virtual model of the NeXT XRT was designed based on the XRT of the SUMIT balloon experiment. From the structure analysis of the virtual model by Marc, we found that the displacement of the XRT housing is small. The maximum displacement is a few µm, which is satisfied with our goal of 10 µm. On the other hand, the alignment bars show a large displacement up to about 90 µm. This is caused because the alignment bars become longer, and the total weight of the thin foils increases due to the larger effective area. This analysis indicates that we have to use stiff alignment bars without reducing the effective area. This result is useful to design a proto-model of the XRT housing. We will examine the result of this FEA analysis by measuring the displacement of the proto-model.