Soft gamma-ray detector for the ASTRO-H Mission

Abstract

ASTRO-H is the next generation JAXA X-ray satellite, intended to carry instruments with broad energy coverage and exquisite energy resolution. The Soft Gamma-ray Detector (SGD) is one of ASTRO-H instruments and will feature wide energy band (40-600 keV) at a background level 10 times better than the current instruments on orbit. SGD is complimentary to ASTRO-H's Hard X-ray Imager covering the energy range of 5-80 keV. The SGD achieves low background by combining a Compton camera scheme with a narrow field-of-view active shield where Compton kinematics is utilized to reject backgrounds. The Compton camera in the SGD is realized as a hybrid semiconductor detector system which consists of silicon and CdTe (cadmium telluride) sensors. Good energy resolution is afforded by semiconductor sensors, and it results in good background rejection capability due to better constraints on Compton kinematics. Utilization of Compton kinematics also makes the SGD sensitive to the gamma-ray polarization, opening up a new window to study properties of gamma-ray emission processes. The ASTRO-H mission is approved by ISAS/JAXA to proceed to a detailed design phase with an expected launch in 2014. In this paper, we present science drivers and concept of the SGD instrument followed by detailed description of the instrument and expected performance.

Modeling the polarization of high-energy radiation from accreting black holes

“…There is no dedicated gamma-ray polarimeter currently in space, but different instruments that could test the predictions of our model are planned for the near future. This is the case of the Soft Gamma-ray Detector (SGD) onboard ASTRO-H, an instrument that will be sensitive to <10% polarization in the 50−200 keV energy band, and it is planned to be launched in 2015 (Tajima et al 2010). The missions of ESA, DUAL and GRI (Gamma-Ray Imager), also include high-energy polarimetric observations, and the French National Research Agency (CNRS) proposes to build a gamma-ray detector and polarimeter in the MeV−GeV energy range (project HARPO, standing for Hermetic Argon Polarimeter).…”

Nonthermal X-ray astronomy

“…Measurement of nonthermal X-ray spectra can be extended to higher energies up to 600 keV with the ASTRO-H Soft Gamma-ray Detector (SGD [51]). The SGD measures soft γ-rays via reconstruction of the Compton-scattered events in a Compton camera that is embedded in a narrow field-of-view active shield.…”

Design and performance of Soft Gamma-ray Detector onboard the Hitomi (ASTRO-H) satellite

“…To fulfill the above objectives, the Hitomi satellite carried the following instruments: a very high-energy-resolution soft x-ray spectrometer (SXS) covering the 0.3-to 12-keV band consisting of thin-foil x-ray optics [Soft X-ray Telescope (SXT)] 7 and a microcalorimeter array (SXS); 8 a soft x-ray imaging spectrometer sensitive in the 0.4-to 12-keV band, consisting of an SXT focusing x-rays onto CCD sensors (Soft x-ray Imager); 9 a hard x-ray imaging spectrometer, sensitive in the 3-to 80-keV band, consisting of multilayer-coated, focusing hard x-ray mirrors (Hard X-ray Telescope) 10 and silicon (Si) and cadmium telluride (CdTe) cross-strip sensors [Hard X-ray Imager (HXI)]; [11][12][13][14][15][16][17][18][19][20] and a soft gamma-ray spectrometer covering the 60-to 600-keV band, utilizing multilayer semiconductor Compton cameras with an active shield [Soft Gamma-ray Detector (SGD)]. [11][12][13][14]21,[22][23][24][25] In the Hitomi mission, the wide-band spectroscopy was expected to play a central role in the investigation of supermassive back holes and physics under extreme conditions. The SGD provided spectral measurements in the highest end of the Hitomi energy band above the HXI's energy band.…”