X-ray imaging spectrometers (XIS) of Astro-E2

Astro-E2 is the fifth Japanese X-ray astronomical satellite and will be launched in 2005. The Astro-E2 X-ray Imaging Spectrometers (XISs) consist of four sets of X-ray CCD cameras. Each CCD camera has an imaging area of 1024×1024 pixels and covers a region of 18′×18′ on the sky combined with an X-ray Telescope. One XIS will utilize back-side illuminated (BI) CCDs, and the other three will be equipped with front-side illuminated (FI) CCDs. The BI CCD has a higher quantum efficiency than the FI CCD below 2 keV, while the FI CCD is more sensitive to X-rays above 5 keV than the BI CCD. Both types of the CCDs have nearly the same energy resolution (full-width at half-maximum (FWHM)=∼130eV at 6 keV). All four cameras have a charge injection capability and 55Fe calibration sources, and we can correct the change of the gain and recover the degradation of the energy resolution due to radiation damage caused by cosmic rays. The sensors are cooled to -90∘C to minimize thermal noise in orbit. The low temperature is also helpful to reduce the influence of the radiation damage.