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We studied the energy spectrum and the large-scale fluctuation of the X-ray background with the ASCA GIS instrument based on the ASCA Medium Sensitivity Survey and Large Sky Survey observations. A total of 91 fields with Galactic latitude |b| > 10 • were selected with a sky coverage of 50 deg 2 and 4.2 Ms of exposure. For each field, non X-ray events were carefully subtracted and sources brighter than ∼ 2 × 10 −13 erg cm −2 s −1 (2-10 keV) were eliminated. Spectral fits with a single power-law model for the individual 0.7-10 keV spectra showed a significant excess below ∼ 2 keV, which could be expressed by an additional thermal model with kT ≃ 0.4 keV or a steep power-law model with a photon index of Γ soft ≃ 6. The 0.5-2 keV intensities of the soft thermal component varied significantly from field to field by 1 σ = 52 +4 −5 %, and showed a maximum toward the Galactic Center. This component is considered to be entirely Galactic. As for the hard power-law component, an average photon index of 91 fields was obtained to be Γ hard = 1.412 ± 0.007 ± 0.025 and the average 2-10 keV intensity was calculated as F hard X = (6.38 ± 0.04 ± 0.64) × 10 −8 erg cm −2 s −1 sr −1 (1 σ statistical and systematic errors). The Galactic component is marginally detected in the hard band. The 2-10 keV intensities show a 1 σ deviation of 6.49 +0.56 −0.61 %, while deviation due to the reproducibility of the particle background is 3.2%. The observed deviation can be explained by the Poisson noise of the source count in the f.o.v. (∼ 0.5 deg 2 ), even assuming a single logN -logS relation on the whole sky. Based on the observed fluctuation and the absolute intensity, an acceptable region of the log N -log S relation was derived, showing a consistent feature with the recent Chandra and XMM-Newton results. The fluctuation of the spectral index was also examined; it implied a large amount of hard sources and a substantial variation in the intrinsic source spectra (Γ S ≃ 1.1 ± 1.0).

We analyzed the ASCA X-ray data of 40 nearby clusters of galaxies, whose intraclustermedium temperature distributes in the range of 0.9-10 keV. We measured the Si and Fe abundances of the intracluster medium, spatially averaging over each cluster, but excluding the central ∼ 0.15h −1 50 Mpc region in order to avoid any possible abundance gradients and complex temperature structures. The Fe abundances of these clusters are 0.2-0.3 solar, with only weak dependence on the temperature of the intracluster medium, hence on the cluster richness. In contrast, the Si abundance is observed to increase from 0.3 to 0.6-0.7 solar from the poorer to richer clusters. These results suggest that the supernovae of both type-Ia and type-II significantly contribute to the metal enrichment of the intracluster medium, with the relative contribution of type-II supernovae increasing towards richer clusters. We suggest a possibility that a considerable fraction of type-II supernova products escaped from poorer systems.

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 results of new, deep Suzaku X-ray observations (160 ks) of the intracluster medium (ICM) in Abell 1689 out to its virial radius, combined with complementary data sets of the projected galaxy distribution obtained from the SDSS catalog and the projected mass distribution from our recent comprehensive weak and strong lensing analysis of Subaru/Suprime-Cam and HST/ACS observations. Faint X-ray emission from the ICM around the virial radius (r vir ∼ 15.′ 6) is detected at 4.0σ significance, thanks to low and stable X-ray background of Suzaku. The Suzaku observations reveal anisotropic gas temperature and entropy distributions in cluster outskirts of r 500 < ∼ r < ∼ r vir correlated with large-scale structure of galaxies in a photometric redshift slice around the cluster. The high temperature (∼ 5.4 keV) and entropy region in the northeastern (NE) outskirts is apparently connected to an overdense filamentary structure of galaxies outside the cluster. The gas temperature and entropy profiles in the NE direction are in good agreement, out to the virial radius, with that expected from a recent XMM-Newton statistical study and with an accretion shock heating model of the ICM, respectively. To the contrary, the other outskirt regions in contact with low density void environments have low gas temperatures (∼ 1.7 keV) and entropies, deviating from hydrostatic equilibrium. These anisotropic ICM features associated with large-scale structure environments suggest that the thermalization of the ICM occurs faster along overdense filamentary structures than along low-density void regions. We find that the ICM density distribution is fairly isotropic, with a threedimentional density slope of −2.29 ± 0.18 in the radial range of r 2500 < ∼ r < ∼ r 500 , and with −1.24in r 500 < ∼ r < ∼ r vir , which however is significantly shallower than the Navarro, Frenk, & White universal matter density profile in the outskirts, ρ ∝ r −3 . A joint X-ray and lensing analysis shows that the hydrostatic mass is lower than spherical lensing one (∼ 60 − 90%) but comparable to a triaxial halo mass within errors, at intermediate radii of 0.6r 2500 < ∼ r < ∼ 0.8r 500 . On the other hand, the hydrostatic mass within 0.4r 2500 is significantly biased as low as < ∼ 60%, irrespective of mass models. The thermal gas pressure within r 500 is, at most, ∼ 50-60% of the total pressure to balance fully the gravity of the spherical lensing mass, and ∼ 30-40% around the virial radius. Although these constitute lower limits when one considers the possible halo triaxiality, these small relative contributions of thermal pressure would require additional sources of pressure, such as bulk and/or turbulent motions.