The XIS is an X-ray Imaging Spectrometer system, consisting of state-of-the-art charge-coupled devices (CCDs) optimized for X-ray detection, camera bodies, and control electronics. Four sets of XIS sensors are placed at the focal planes of the grazing-incidence, nested thin-foil mirrors (XRT: X-Ray Telescope) onboard the Suzaku satellite. Three of the XIS sensors have front-illuminated CCDs, while the other has a back-illuminated CCD. Coupled with the XRT, the energy range of 0.2-12 keV with energy resolution of 130 eV at 5.9 keV, and a field of view of 18 × 18 are realized. Since the Suzaku launch on 2005 July 10, the XIS has been functioning well.

We have developed a framework for the Monte-Carlo simulation of the X-Ray Telescopes (XRT) and the X-ray Imaging Spectrometers (XIS) onboard Suzaku, mainly for the scientific analysis of spatially and spectroscopically complex celestial sources. A photon-by-photon instrumental simulator is built on the ANL platform, which has been successfully used in ASCA data analysis. The simulator has a modular structure, in which the XRT simulation is based on a ray-tracing library, while the XIS simulation utilizes a spectral "Redistribution Matrix File" (RMF), generated separately by other tools. Instrumental characteristics and calibration results, e.g., XRT geometry, reflectivity, mutual alignments, thermal shield transmission, build-up of the contamination on the XIS optical blocking filters (OBF), are incorporated as completely as possible. Most of this information is available in the form of the FITS (Flexible Image Transport System) files in the standard calibration database (CALDB). This simulator can also be utilized to generate an "Ancillary Response File" (ARF), which describes the XRT response and the amount of OBF contamination. The ARF is dependent on the spatial distribution of the celestial target and the photon accumulation region on the detector, as well as observing conditions such as the observation date and satellite attitude. We describe principles of the simulator and the ARF generator, and demonstrate their performance in comparison with in-flight data.

We present X-ray observations of the northern outskirts of the relaxed galaxy cluster A1413 with Suzaku, whose XIS instrument has the low intrinsic background needed to make measurements of these low surface brightness regions. We excise 15 point sources superimposed on the image above a flux of 1 × 10 −14 erg cm −2 s −1 (2-10 keV) using XMM-Newton and Suzaku images of the cluster. We quantify all known systematic errors as part of our analysis, and show our statistical errors encompasses them for the most part. Our results extend previous measurements with Chandra 1 and XMM-Newton, and show a significant temperature drop to about 3 keV at the virial radius, r 200 . Our entropy profile in the outer region (> 0.5 r 200 ) joins smoothly onto that of XMM-Newton, and shows a flatter slope compared with simple models, similar to a few other clusters observed at the virial radius. The integrated mass of the cluster at the virial radius is approximately 7.5 × 10 14 M ⊙ and varies by about 30% depending on the particular method used to measure it.

One of the advantages of the X-ray Imaging Spectrometer (XIS) system on board Suzaku is its low and stable non-X-ray background (NXB). In order to make the best use of this advantage, modeling the NXB spectra with high accuracy is important to subtract them from the spectra of on-source observations. We construct an NXB database by collecting XIS events when the dark Earth covers the XIS FOV. The total exposure time of the NXB data is about 785 ks for each XIS. It is found that the count rate of the NXB anti-correlates with the cut-off-rigidity and correlates with the count rate of the PIN upper discriminator (PIN-UD) in Hard X-ray Detector on board Suzaku. We thus model the NXB spectrum for a given on-source observation by employing either of these parameters and obtain a better reproducibility of the NXB for the model with PIN-UD than that with the cut-off-rigidity. The reproducibility of the NXB model with PIN-UD is 4.55-5.63 % for each XIS NXB in the 1-7 keV band and 2.79-4.36 % for each XIS NXB in the 5-12 keV band for each 5 ks exposure of the NXB data. This NXB reproducibility is much smaller than the spatial fluctuation of 1 arXiv:0803.0616v1 [astro-ph] 5 Mar 2008 the cosmic X-ray background in the 1-7 keV band, and is almost comparable to that in the 5-12 keV band.

We present an analysis of a Suzaku observation of the link region between the galaxy clusters A 399 and A 401. We obtained the metallicity of the intracluster medium (ICM) up to the cluster virial radii for the first time. We determine the metallicity where the virial radii of the two clusters cross each other (∼ 2 Mpc away from their centers) and found that it is comparable to that in their inner regions (∼ 0.2 Z ⊙ ). It is unlikely that the uniformity of metallicity up to the virial radii is due to mixing caused by a cluster collision. Since the ram-pressure is too small to strip the interstellar medium of galaxies around the virial radius of a cluster, the fairly high metallicity that we found there indicates that the metals in the ICM are not transported from member galaxies by ram-pressure stripping. Instead, the uniformity suggests that the proto-cluster region was extensively polluted with metals by extremely powerful outflows (superwinds) from galaxies before the clusters formed. We also searched for the oxygen emission from the warm-hot intergalactic medium in that region and obtained a strict upper limit of the hydrogen density (n H < 4.1 × 10 −5 cm −3 ).