Development of a p-type CCD for NeXT: the next Japanese X-ray astronomical satellite mission

The next Japanese X-ray astronomical satellite mission, NeXT, was proposed to ISAS/JAXA following the Astro-E2 Suzaku satellite which was launched in July 2005. We develop an X-ray CCD camera system, SXI (Soft X-ray Imager), for NeXT. The Hard X-ray Telescope (HXT) onboard NeXT provides imaging capability up to 80 keV, using the multilayer-coated X-ray mirror technology, called "Supermirror", newly developed in Japan. SXI is one of the focal plane detectors of HXT, which covers the soft energy band in the 0.5-12 keV in the baseline and 0.3-25 keV in the goal. We develop p-type CCDs for the baseline of SXI because p-type CCDs have been successfully used for previous X-ray astronomical satellites. We developed a prototype of a p-type CCD for SXI, called "CCD-NeXT1". CCD-NeXT1 is a frame-transfer CCD with two readout nodes. The image area of CCD-NeXT1 consists of 2 K x 2 K pixels with a pixel size of 12 mu m x 12 mu m. We evaluated performance of CCD-NeXT1 devices, KG-4 and KG-5. The energy resolution was 141.8 +/- 0.6 eV full width at half maximum at 5.9 keV, the readout noise was 4.7 +/- 0.2 e(-), the horizontal CTI was < 5.1 x 10(-7), and the vertical CTI was < 2.4 x 10(-7) for KC-5. The performance of KG-4 was more or less the same as that of KG-5. The thickness of the depletion layer was 82 +/- 7 mu m for KG-4 and 76 +/- 6 mu m for KG-5. We conclude that our technology for p-type CCDs is sufficient to satisfy the CCD performance for the baseline of SXI.