With ASTRO-H, we expect to achieve an area of about 300 cm2 a 30keV with a typical angular resolution of 60-90 arcsec (HPD) By assuming a background level of 1 x10-4counts/s/cm2/keV, in which the non X-ray background is dominant, the source detection limit in 1000 ksec would be roughly 10-14 erg cm2 s-1 in terms of the 10—80 keV flux for a power-law spectrum with a photon index of 2. This is about two orders of magnitude better than present instrumentation, so will give a breakthrough in our understanding of hard X-ray spectra. With this sensitivity, 30-40 % of hard X-ray CosmicBackground would be be resolved.
In addition to the imaging observations below 80keV, the SGD will provide a high sensitivity in the soft Gamma-ray region to match thesensitivity of the HXT/HXI combination. The extremely low background brought by the new concept of a narrow-FOV Compton telescope adopted for the SGD will provide sensitive gamma-ray spectra up to 600keV, with moderate sensitivity for polarization measurements.
SXS spectroscopy of extended sources can reveal line broadening and Doppler shifts due to turbulent or bulk velocities. This capability enables the spectral identification of cluster mergers, SNR ejecta dispersal patterns, the structure of AGN and starburst winds, and the spatially dependent abundance pattern in clusters and elliptical galaxies. SXS can also measure the optical depths of resonance absorption lines, from which the degree and spatial extent of turbulence can be inferred. Additionally, SXS can reveal the presence of relatively rare elements in SNRs and other sources through its high sensitivity to low equivalent width emission lines. The low SXS background ensures that the observations of almost all line rich objects will be photon limited rather than background limited.
XMM-Newton and Suzaku spectra frequently show time-variable absorption and emission features in the 5—10 keV band. If these features are due to Fe, they represent gas moving at very high velocities with both red and blue shifted components from material presumably near the event horizon. CCD resolution is too low and the required grating exposures are too long to properly characterize the velocity field and ionization of this gas and determine whether it is from close to the black hole or from high velocity winds. SXS, in combination with HXI, provides a dramatic increase in sensitivity over Suzaku, enabling measurements that probe the geometry of the central regions of ~50 AGNs on the orbital timescale of the Fe producing region.