Energy-Scale Calibration of the Suzaku X-Ray Imaging Spectrometer Using the Checker Flag Charge Injection Technique in Orbit

TL;DR

This paper details the in-orbit calibration of the Suzaku X-ray Imaging Spectrometer's energy scale and resolution using the checker flag charge injection technique, compensating for radiation damage effects.

Contribution

It introduces a precise in-orbit CTI measurement method with CFCI and implements a time-dependent calibration to improve energy resolution.

Findings

CTI correction improved energy resolution from 230 eV to 190 eV at 5.9 keV

CFCI technique accurately measures charge transfer inefficiency in orbit

Calibration database now includes time-dependent energy scale adjustments

Abstract

The X-ray Imaging Spectrometer (XIS) on board the Suzaku satellite is an X-ray CCD camera system that has superior performance such as a low background, high quantum efficiency, and good energy resolution in the 0.2-12 keV band. Because of the radiation damage in orbit, however, the charge transfer inefficiency (CTI) has increased, and hence the energy scale and resolution of the XIS has been degraded since the launch of July 2005. The CCD has a charge injection structure, and the CTI of each column and the pulse-height dependence of the CTI are precisely measured by a checker flag charge injection (CFCI) technique. Our precise CTI correction improved the energy resolution from 230 eV to 190 eV at 5.9 keV in December 2006. This paper reports the CTI measurements with the CFCI experiments in orbit. Using the CFCI results, we have implemented the time-dependent energy scale and resolution to the Suzaku calibration database.