New CTI Correction Method for Spaced-Row Charge Injection of the Suzaku X-Ray Imaging Spectrometer

Abstract

The charge transfer inefficiency (CTI) of the X-ray CCDs aboard the Suzaku satellite (X-ray Imaging Spectrometers: XIS) has increased since the launch due to radiation damage, and the energy resolution has been degraded. To improve the CTI, we have applied a spaced-row charge injection (SCI) technique to the XIS in orbit; by injecting charges into CCD rows periodically, the CTI is actively decreased. The CTI in the SCI mode depends on the distance between a signal charge and a preceding injected row, and the pulse height shows periodic positional variations. Using in-flight data of onboard calibration sources and of the strong iron line from the Perseus cluster of galaxies, we studied the variation in detail. We developed a new method to correct the variation. By applying the new method, the energy resolution (FWHM) at 5.9 keV in 2008 March is $\sim$155 eV for the front-illuminated CCDs and $\sim$175 eV for the back-illuminated CCD.