In-orbit performance of the soft X-ray imaging system aboard Hitomi (ASTRO-H)

TL;DR

This paper reports on the in-orbit performance, calibration, and initial results of the soft X-ray imaging system aboard Hitomi, demonstrating its capabilities and limitations within a limited observation period.

Contribution

It provides the first in-orbit performance verification and calibration of Hitomi's soft X-ray imaging system using limited data, including measurements of imaging quality and background levels.

Findings

Field of view verified with Perseus cluster image

Half power diameter of about 1.3' measured from Crab pulsar data

Background level significantly lower than Suzaku XIS-BI

Abstract

We describe the in-orbit performance of the soft X-ray imaging system consisting of the Soft X-ray Telescope and the Soft X-ray Imager aboard Hitomi. Verification and calibration of imaging and spectroscopic performance are carried out making the best use of the limited data of less than three weeks. Basic performance including a large field of view of 38'x38' is verified with the first light image of the Perseus cluster of galaxies. Amongst the small number of observed targets, the on-minus-off pulse image for the out-of-time events of the Crab pulsar enables us to measure a half power diameter of the telescope as about 1.3'. The average energy resolution measured with the onboard calibration source events at 5.89 keV is 179 pm 3 eV in full width at half maximum. Light leak and cross talk issues affected the effective exposure time and the effective area, respectively, because all the observations were performed before optimizing an observation schedule and parameters for the dark level calculation. Screening the data affected by these two issues, we measure the background level to be 5.6x10^{-6} counts s^{-1} arcmin^{-2} cm^{-2} in the energy band of 5-12 keV, which is seven times lower than that of the Suzaku XIS-BI.