The hard X-ray imaging system onboard ASTRO-H consists of two identical mirror-detector pairs (Hard X-ray Telescope (HXT) and Hard X-ray Imager (HXI)). The HXT has conical-foil mirrors with graded multilayer reflecting surfaces that provide a 5-80 keV energy range. The effective area of the HXT
is maximized for a long focal length, with current design value of 12 m giving an effective area of ~300 cm2 at 30 keV. A depth-graded multi-layer mirror reflects X-rays not only by total external reflection but also by Bragg reflection. In order to obtain high reflectivity up to 80~keV, the HXT’s consist of a stack of multi-layers with different sets of periodic length and number of layer pairs with a carbon/platinum coating.
The HXI consists of four-layers of 0.5 mm thick Double-sided Silicon Strip
Detectors (DSSD) and one layer of 0.5—1 mm thick CdTe imaging detector.
In this configuration, soft X-ray photons will be absorbed in the Si part (DSSD), while hard X-ray photons go through the Si part and are detected by the newly developed CdTe double strip detector. Fast timing response of silicon strip detector and CdTe strip detector allows us to place the whole detector inside very deep well of the active shield made of BGO (Bi4G3O12). Signal from the BGO shield is used to reject background events. The total thickness of the four DSSDs is 2 mm, the same as that of the PIN detector of the HXD onboard Suzaku. The DSSDs cover the energy below 30 keV while the CdTe strip detector covers the 20-80 keV band.