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

TL;DR

This paper presents a new correction method for charge transfer inefficiency in Suzaku's X-ray CCDs, significantly improving energy resolution after radiation damage using a spaced-row charge injection technique.

Contribution

The authors developed a novel correction method for CTI variations caused by SCI, enhancing spectral resolution of Suzaku's XIS in orbit.

Findings

Energy resolution at 5.9 keV improved to ~155 eV (front-illuminated) and ~175 eV (back-illuminated).

The correction method effectively compensates for periodic CTI variations.

Demonstrated improved spectral performance post-correction.

Abstract

The charge transfer inefficiency (CTI) of the X-ray CCDs on board 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 at March 2008 is ~155 eV for the front-illuminated CCDs and ~175 eV for the back-illuminated CCD.