High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.

We present the design parameters, production process, and in-flight performance of the X-ray telescope (XRT) onboard Suzaku. The imaging capability is significantly improved over the ASCA XRT, which had half-power diameters of ${3\rlap {.}{}^{\mathrm {\prime }}6}$, to ${1\rlap {.}{}^{\mathrm {\prime }}8}$–${2\rlap {.}{}^{\mathrm {\prime }}3}$ for all four XRT-I modules. The optical axes are found to be distributed within a radius of ${1\rlap {.}{}^{\mathrm {\prime }}3}$, which makes the observation efficiency of all the XRTs more than 97% at the XIS-default observing position. The vignetting over the XIS field of view predicted via ray-tracing coincides with that measured for observations of the Crab Nebula to within $\sim 10\%$. Contemporaneous fits of a power law to all of the XIS spectra of the Crab Nebula taken at the two standard observing positions (XIS/HXD-default positions) gives a flux consistent with that obtained by Toor and Seward (1974, AJ, 79, 995) to within $\sim 2\%$. The pre-collimator on the top of each XRT module successfully reduces the intensity of the stray light from the $20'$ and $50'$-off directions down to the level of pre-flight expectations.

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.

Abstract. The ASCA satellite made a quick followup observation of GRB 970828 and detected its fading X-ray afterglow at the position localized by the All-Sky Monitor on the Rossi XTE satellite. Because of the quickness, the afterglow was still rather bright (∼ 4 10 −13 ergs cm −2 s −1 : 2 − 10 keV), and ASCA obtained the data of good quality. We found the spectral features of the absorption which implies a column density of 4.1 10 21 cm −2 at z = 0, together with an emission line at ∼ 5 keV. The line could be red shifted Fe K α line. Hence, it suggests a relatively small red shift z ≈ 0.33 for this GRB.

The temperature distribution of the intracluster medium (ICM) in the Virgo Cluster of galaxies has been derived from extensive mapping observations with ASCA covering an area of 19 deg2. In the spectral analysis, the inner region within a radius of D60@ from M87 is characterized by an ICM temperature of kT D 2.5 keV with little variation. On the other hand, the outer regions indicate signiÐcant variation of the temperature with an amplitude of about 1 keV. The temperature map was produced from the hardness ratio (HR) values with a resolution of about 5@. Besides the previously reported hot region with kT [ 4 keV between M87 and M49, several hot regions with kT \ 3È4 keV are detected in the cluster outskirts. The autocorrelation function for the HR variation shows that the temperature variation is correlated within a size of about 300 kpc, suggesting that gas blobs falling in the Virgo Cluster have a typical size of groups of galaxies. A correlation with the velocity dispersion of member galaxies shows that only the northwest region indicates an unusually large value of 2È4. The upper b spec limit for extended nonthermal emission in the Virgo Cluster is obtained to be ergs s~1 in L X D 9 ] 1041 the 2È10 keV band. We discuss that these features consistently indicate that the Virgo Cluster is in a relatively early stage of the cluster evolution.