Masanori Ohno

Suzaku‐WAM, Konus‐Wind, and Swift‐BAT observations of the prompt emission of the highest redshift GRB 050904

We present the results of the highest redshift GRB 050904 from joint spectral analyses among Swift/BAT, Konus‐Wind and Suzaku‐WAM covering a wide energy range of 15–5000 keV. The peak energy was first measured at 338−93+168 keV, corresponding to 2465−678+1225 keV in the source frame. This is one of the highest value that has been ever meaured. The derived spectral and energetic parameters are consisitent with the Amati relation, but not with the Ghirlada relation. This implies that the circumburst density of this burst might be larger than the nominal value, as suggested by other wavelength observations. We also found that the burst could be an outlier in Yonetoku relation.

In-orbit performance and calibration of the Hard X-ray Imager onboard Hitomi (ASTRO-H)

Abstract. The Hard X-ray Imager (HXI) onboard Hitomi (ASTRO-H) is an imaging spectrometer covering hard x-ray energies of 5 to 80 keV. Combined with the Hard X-ray Telescope, it enables imaging spectroscopy with an angular resolution of 1′.7 half-power diameter, in a field of view of 9′  ×  9′. The main imager is composed of four layers of Si detectors and one layer of CdTe detector, stacked to cover a wide energy band up to 80 keV, surrounded by an active shield made of Bi4Ge3O12 scintillator to reduce the background. The HXI started observations 12 days before the Hitomi loss and successfully obtained data from G21.5–0.9, Crab, and blank sky. Utilizing these data, we calibrate the detector response and study properties of in-orbit background. The observed Crab spectra agree well with a powerlaw model convolved with the detector response, within 5% accuracy. We find that albedo electrons in specified orbit strongly affect the background of the Si top layer and establish a screening method to reduce it. The background level over the full field of view after all the processing and screening is as low as the preflight requirement of 1  −  3  ×  10−4  counts s−1 cm−2 keV−1.