Factsheets/brochures about Hitomi (ASTRO-H)

 

The payload

The mission carries a set of four different instruments: two hard X-ray images (HXI) with dedicated hard X-ray telescopes, one micro-calorimeter (SXS) and one CCD camera (SXI), each behind dedicated soft X-ray telescopes. A non-focusing detector will also cover the soft gamma-ray range up to 600 keV (SGD). All instruments are co-aligned and will operate simultaneously. The ASTRO-H Quick Reference document is also availble in PDF format for your convenience.

Effective area for the different instruments onboard ASTRO-H

 

SXS

The Soft X-ray Spectrometer System (SXS) is a combination of a soft X-ray telescope (SXT) and the X-ray calorimeter spectrometer (XCS). The latter is placed at the focal length of 5.6 m. The effective area is optimized at high energies, with 210 cm2 at 6 keV, 50 cm2 at 0.5 keV, and 160 cm2 at 1 keV. The energy range will span from 0.3 to 12 keV with a superb energy resolution of 7 eV (specifications) at 6 keV. The goal is to reach 4 eV spectral resolution, which would allow a spectral power of R=1600 at 6 keV (current best estimate is 5 eV). In contrast to gratings, the spectral power increases as a function of energy. The microcalorimeter will be an array of 6x6 pixels of pixel size 814x814 microns2, operating at 50 mK, with a field-of-view of 3'.05x3'.05 (i.e., a pixel scale of 30"/pixel) and angular resolution of 1.7' half-power diameter (goal of 1.3'; the current best estimate already reaches this value). The XCS will also carry a suite of filters: X-ray filters to attenuate the X-ray signal for bright X-ray sources (one Be-type to  block the low-energy photons and one neutral density for very bright sources and background calibration), and one polyimide filter to avoid contamination in early phases of the mission. Two open positions are also available. In addition, one filter wheel position with a 55Fe source can be inserted for backup calibration purposes. Novel Modulated X-ray Sources are also mounted below the filter wheel for calibration as well. The filters are necessary not only to avoid saturation, but also because the energy resolution depends on the X-ray count rate. Energy event grades are defined, with the best calorimeter resolution obtained only for high-resolution (HR) and medium-resolution (MR) events. Finally, the required time assignment resolution of the SXS is 80 microseconds, whereas the maximum counting rate should reach 150 count/s/pixel.

SXS-FW

Filter positions for the SXS.

 

sxs eff cmp

Effective area of the SXS compared to grating instruments (RGS, HETG, LETG) and the Suzaku XRS.

 

sxsgrades

Grade definition for the SXS. The calorimeter resolution can only be reached for HR and MR events.

 

References: a) The ASTRO-H mission, Takahashi et al. 2010, Proceedings of the SPIE, Volume 7732. b) The High-Resolution X-ray Microcalorimeter Spectrometer System for the SXS on ASTRO-H, Mitsuda et al. 2010, Proceedings of the SPIE, Volume 7732.

 

SXI

The Soft X-ray Imager (SXI) consists of an X-ray CCD camera placed at the focus (5.6 m) of a dedicated soft X-ray telescope (SXT). The SXI will be composed of 4 p-channel back-illuminated CCDs in a 2x2 array layout (with 20" gaps between the chips). The effective area of the SXI should reach 360 cm2 at 6 keV and 214 cm2 at 0.5 keV, whereas the energy range will span from 0.4 to 12 keV. The angular resolution of the SXI will be similar to the SXS, but the field-of-view will be much larger, up to 38'x38', with a pixel scale of 1.74" (640x640 pixels for one CCD). The SXI will allow the observers to characterize the immediate X-ray sky around the field-of-view covered by the SXS. The energy resolution of the SXI will be typical of X-ray CCDs, i.e., less than 150 eV at 6 keV (R=40). The time resolution will be 4 seconds. The SXI is considered as one of the suite of instruments onboard ASTRO-H that will probide broad-band coverage from the soft X-rays to the gamma-ray regime.

 

sxi

Layout of the SXI array. The field-of-view of the SXS is also overlaid,

 

References: a) The ASTRO-H mission, Takahashi et al. 2010, Proceedings of the SPIE, Volume 7732. b) Soft X-ray Imager (SXI) onboard ASTRO-H, Tsunemi et al. 2010, Proceedings the SPIE, Volume 7732.

 

HXI

The Hard X-ray Image (HXI) is composed of both the hard X-ray imaging system and the Hard X-ray Telescope (HXT). In fact, there are 2 identical hard X-ray imagers, each at the focus of a dedicated HXT at a focal length of 12 m, i.e., about twice the focal lengths of the SXT. Hence, the HXI detectors are not placed on the same platform as the soft X-ray detectors. The detectors use the technology of Si strip detectors (four layers) to absorb the soft X-rays below 30 keV, and include one layer of CdTe strip to absorb the hard X-rays (20-80 keV). The HXI will provide images and spectra in the 5-80 keV range with moderate energy resolution (0.9 keV at 14 keV in the double-sided Si layers, 1.5-1.7 keV in the double-sided CdTe layer). The effective area is about 300 cm2 at 30 keV. The angular resolution in the HXI is 1.7' for a field of view of 9x9 arcmin2. An active BGO shield will work as veto counter and suppress a significant amount of background. The fast timing response of the HXI detectors will allow bright sources to be observed without pile-up. The HXI will operate in one single mode, but users will be able to select events in all HXI layers or in the top Si strip layer for faint sources.

hxidet

Schematic view of the HXI with the double-sided Si strip detectors (DSSD) and CdTe double-sided strip detector (DS-CdTe) shown

 

hxien

Energy resolution of the HXI in the DSSD layers (left) and in the DS-CdTe layer (right)

 

hxieffic

Detection efficiency of the HXI for the top DSSD layer (black) and for all layers (DSSD and DSD-CdTe). Soft X-rays (<10 keV) tend to be detected mainly in the top layer

hxt hxi back

Continuum sensitivity of ASTRO-H showing the power of the focussing hard X-ray telescope

 

References: a) The ASTRO-H mission, Takahashi et al. 2010, Proceedings of the SPIE, Volume 7732. b) Hard X-ray imager (HXI) for the ASTRO-H Mission, Kokubun et al. 2010, Proceedings the SPIE, Volume 7732.

 

SGD

 The Soft Gamma-ray Detector (SGD) is a non-imaging detector that will cover the 10-600 keV energy range. Compared to Suzaku and its hard X-ray detector, the sensitivity of the SGD should be 10 times better at 300 keV.  The SGD uses the concept of a narrow field-of-view Compton telescope (33x33 arcmin2 below 150 keV, 600x600 arcmin2 above 150 keV) which will efficiently suppress the background. In addition SGD should also have polarimetric capabilities. Photons will generally interact by photoelectric absorption in the CdTe detector (photo-abs mode). However, photons with energies above 40 keV may interact twice in the detector: first by Compton scattering in the Si pad detectors, and then by photoelectric absorption in the CdTe detector. This is the Compton mode of the SGD. The energy and direction (as a cone in the sky) can then be retrieved for each incident gamma-ray photon. The effective area of the SGD is 150 cm2 at 30 keV in the photo-abs mode and 20 cm2 at 100 keV in the Compton mode. The SGD will operate in one single mode but, like for the HXI, events can be selected depending on the source flux: for normal sources, the Compton mode events can be selected, while the Compon mode and the photo-absorption mode events can be selected for bright sources. The energy resolution will be about 2 keV at 40 keV in the photo-abs mode and 4 keV at 40 keV in the Compton mode.

sgddet

Schematic view of the SGD. The SGD has 6 Compton camera units (one shown on the right)

 

sgdaeff compton

Effective area of the SGD in the Compton mode (two interactions)

 

References: a) The ASTRO-H mission, Takahashi et al. 2010, Proceedings of the SPIE, Volume 7732. b) Soft gamma-ray detector for the ASTRO-H Mission, Tajima et al. 2010, Proceedings the SPIE, Volume 7732.