Performance of the Charge-Injection Capability of Suzaku XIS
Dotani, Tadayasu; Katsuda, Satoru; Yamaguchi, Hiroya; Koyama, Katsuji; Hayashida, Kiyoshi; Nakajima, Hiroshi; Matsumoto, Hironori; Namiki, Masaaki; Tsuru, Takeshi Go; Murakami, Hiroshi; Ozaki, Masanobu; Tsunemi, Hiroshi; Torii, Ken'ichi; Shoji, Masayuki; Matsuura, Daisuke; Miyauchi, Tomofumi; Bautz, Mark W.; Kissel, Steve E.; LaMarr, Beverly; Prigozhin, Gregory Y.
Japan, United States
Abstract
A charge-injection technique is applied to the X-ray CCD camera, XIS (X-ray Imaging Spectrometer) aboard Suzaku. The charge transfer inefficiency (CTI) in each CCD column (vertical transfer channel) is measured by the injection of charge packets into a transfer channel and subsequent readout. This paper reports on the performances of the charge-injection capability based on the ground experiments using a radiation-damaged device, and in-orbit measurements of the XIS. The ground experiments show that charges are stably injected with a dispersion of 91eV in FWHM in a specific column for the charges equivalent to an X-ray energy of 5.1keV. This dispersion width is significantly smaller than that of the X-ray events of 113eV (FWHM) at approximately the same energy. The amount of charge loss during transfer in a specific column, which is measured with the charge-injection capability, is consistent with that measured with the calibration source. These results indicate that the charge-injection technique can accurately measure column-dependent charge losses, rather than the calibration sources. The column-to-column CTI correction to the calibration source spectra significantly reduces the line widths compared to those with a column-averaged CTI correction (from 193eV to 173eV in FWHM on an average at the time of one year after the launch). In addition, this method significantly reduces the low-energy tail in the line profile of the calibration source spectrum.