Ground calibration of CCD camera (XIS) with front-illuminated chips onboard Astro-E2

摘要

We report on the results of the ground calibration of Astro-E2/XIS with front-illuminated (FI) chips. The sensors have basically the same performance as that of Astro-E/XIS. However, there are some improved points: (1) A 55Fe radio isotope is equipped on a door, and (2) a charge injection (CI)capability (described below) is added. The FI sensors have been calibrated at Kyoto University, Osaka University, and MIT. At Kyoto University we focus on the high energy range (>1.5 keV). We measured the gain, energy resolution, and quantum efficiency as the function of energy by using characteristic X-rays for each sensor. An energy resolution of 130 eV@5.9 keV (FWHM) and a quantum efficiency of 82%@6.4 keV are achieved. After XIS is launched, the Charge Transfer Inefficiency (CTI) increases due to the radiation damage by cosmic rays. Then XIS equips the CI capability to calibrate and compensate the increase of the CTI. In order to utilize the CI capability, the amount of charge injected into the CCDs is expected to be kept constant. The time variability of the amount of the injected charge is estimated.