Origin of the in-orbit instrumental background of the Hard X-ray Imager onboard Hitomi

Kouichi Hagino , Hirokazu Odaka , Goro Sato , Tamotsu Sato , Hiromasa Suzuki , Tsunefumi Mizuno , Madoka Kawaharada , Masanori Ohno (1) , Kazuhiro Nakazawa , Shogo B. Kobayashi , Hiroaki Murakami , Katsuma Miyake , Makoto Asai , Tatsumi Koi , Greg Madejski , Shinya Saito , Dennis H. Wright , Teruaki Enoto , Yasushi Fukazawa , Katsuhiro Hayashi , Jun Kataoka , Junichiro Katsuta , Motohide Kokubun , Philippe Laurent (2, 3) , François Lebrun (2, 3) , Olivier Limousin (3) , Daniel Maier (3) , Kazuo Makishima , Kunishiro Mori , Takeshi Nakamori , Toshio Nakano , Hirofumi Noda , Masayuki Ohta , Rie Sato , Hiroyasu Tajima , Hiromitsu Takahashi , Tadayuki Takahashi , Shin'Ichiro Takeda , Takaaki Tanaka , Yukikatsu Terada , Hideki Uchiyama , Yasunobu Uchiyama , Shin Watanabe , Kazutaka Yamaoka , Yoichi Yatsu , Takayuki Yuasa

1 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
2 APC (UMR_7164) - AstroParticule et Cosmologie
3 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation

Understanding and reducing in-orbit instrumental backgrounds are essential to achieving high sensitivity in hard x-ray astronomical observations. The observational data of the Hard X-ray Imager (HXI) onboard the Hitomi satellite provide useful information on the background components due to its multilayer configuration with different atomic numbers: the HXI consists of a stack of four layers of Si (Z  =  14) detectors and one layer of cadmium telluride (CdTe) (Z  =  48, 52) detector surrounded by well-type Bi4Ge3O12 active shields. Based on the observational data, the backgrounds of the top Si layer, the three underlying Si layers, and the CdTe layer are inferred to be dominated by different components, namely, low-energy electrons, albedo neutrons, and proton-induced radioactivation, respectively. Monte Carlo simulations of the in-orbit background of the HXI reproduce the observed background spectrum of each layer well, thereby quantitatively verifying the above hypothesis. In addition, we suggest the inclusion of an electron shield to reduce the background.

Mots clés: Hitomi; ASTRO-H; hard x-ray imager; hard x-rays; background; simulation

Domaines: Instrumentations et Détecteurs [physics.ins-det]

Kouichi Hagino, Hirokazu Odaka, Goro Sato, Tamotsu Sato, Hiromasa Suzuki, et al.. Origin of the in-orbit instrumental background of the Hard X-ray Imager onboard Hitomi. J.Astron.Telesc.Instrum.Syst., 2020, 6 (4), pp.046003. ⟨10.1117/1.JATIS.6.4.046003⟩. ⟨hal-03129440⟩