THE GROUND CALIBRATION OF THE BACK-SIDE ILLUMINATED CCD CAMERA OF X-RAY IMAGING SPECTROMETER (XIS) ONBOARD ASTRO-E2 (SUZAKU)

摘要

We report on the results of the ground calibration of the back-side illuminated (BI) Charge-Coupled Device (CCD) onboard Suzaku(Astro-E2). The BI CCD has higher quantum efficiency (QE) below ～4keV than Front-side illuminated (FI) CCDs. By chemisorption charging process, furthermore, the BI chip achieved very good energy resolution comparable to the FI chip. However, several problems were found by our ground calibration. One of them is charge trailing, and we corrected this phenomenon by a newly developed method, "Charge Trail Correction". Another problem is that the constant split threshold, a key parameter for the Grade method, gives a poor performance for the BI chip. Thus we introduced a new Grade method with a variable split threshold depending on the incident X-ray energy. Analyzing the ground calibration data with these new methods, we built the response function of BI CCD.