Inorbit Performance of the Hard X-ray Telescope (HXT) on board the Hitomi (ASTRO-H) satellite

TL;DR

This paper evaluates the in-orbit performance of Hitomi's Hard X-ray Telescopes, confirming their characteristics remain consistent with ground measurements and validating their imaging spectroscopy capabilities in the 5-80 keV range.

Contribution

It provides the first in-orbit characterization of Hitomi's HXTs, demonstrating their stability and performance post-launch compared to ground tests.

Findings

Half power diameters are 1.59 and 1.65 arcmin, consistent with ground measurements.

No significant change in HXT characteristics after launch.

Crab spectrum parameters match canonical values.

Abstract

Hitomi (ASTRO-H) carries two Hard X-ray Telescopes (HXTs) that can focus X-rays up to 80 keV. Combined with the Hard X-ray Imagers (HXIs) that detect the focused X-rays, imaging spectroscopy in the high-energy band from 5 keV to 80 keV is made possible. We studied characteristics of HXTs after the launch such as the encircled energy function (EEF) and the effective area using the data of a Crab observation. The half power diameters (HPDs) in the 5--80 keV band evaluated from the EEFs are 1.59 arcmin for HXT-1 and 1.65 arcmin for HXT-2. Those are consistent with the HPDs measured with ground experiments when uncertainties are taken into account. We can conclude that there is no significant change in the characteristics of the HXTs before and after the launch. The off-axis angle of the aim point from the optical axis is evaluated to be less than 0.5 arcmin for both HXT-1 and HXT-2. The best-fit parameters for the Crab spectrum obtained with the HXT-HXI system are consistent with the canonical values.