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 report the detection of a fully resolved, Compton-scattered emission line in the X-ray spectrum of the massive binary GX 301Ϫ2 obtained with the High Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory. The iron Ka fluorescence line complex observed in this system consists of an intense narrow component centered at an energy of keV and a redward shoulder that extends down E p 6.40 to ∼6.24 keV, which corresponds to an energy shift of a Compton backscattered iron Ka photon. From detailed Monte Carlo simulations and comparisons with the observed spectra, we are able to directly constrain the physical properties of the scattering medium, including the electron temperature and column density, as well as an estimate for the metal abundance.

We present results from Chandra and XMM-Newton observations of a bright group of galaxies, HCG 62. There are two cavities at about $30{}^{\prime\prime}$ northeast and $20{}^{\prime\prime}$ southwest of the central galaxy in the Chandra image. The energy spectrum shows no significant change in the cavity compared with that in the surrounding region. The radial X-ray profile is described by the sum of the 3-$\beta$ components with core radii of about 2, 10, and 160 kpc. We studied the radial distributions of the temperature and the metal abundance with a joint spectral fit for both data; two temperatures were required in the inner $r< 2'$ (36 kpc) region. A sharp drop of the temperature at $r \sim 5'$ implies a gravitational mass density even lower than the gas density, suggesting that the gas may not be in hydrostatic equilibrium. The Fe and Si abundances are 1–2 solar at the center, and drop to about 0.1 solar at $r \sim 10'$. The O abundance is less than 0.5 solar, and shows a flatter profile. The observed metal distribution supports the view that iron and silicon are produced by type Ia supernova (SN Ia) in the central galaxy, while galactic winds by SN II have caused a wide distribution of oxygen. The supporting mechanism of the cavity is discussed. The pressure for the sum of electrons and the magnetic field is too low to displace the hot group gas, and the required pressure due to high-energy protons is nearly 700-times higher than the electron pressure. This leaves the origin of the cavities a puzzle; we also discuss other possible origins of the cavities.

The X-Ray Spectrometer (XRS) has been designed to provide the Suzaku Observatory with non-dispersive, high-resolution X-ray spectroscopy. As designed, the instrument covers the energy range 0.3 to 12 keV, which encompasses the most diagnostically rich part of the X-ray band. The sensor consists of a 32-channel array of X-ray microcalorimeters, each with an energy resolution of about 6 eV. The very low temperature required for operation of the array (60 mK) is provided by a four-stage cooling system containing a single-stage adiabatic demagnetization refrigerator, a superfluid-helium cryostat, a solid-neon dewar, and a single-stage, Stirling-cycle cooler. The Suzaku/XRS is the first orbiting X-ray microcalorimeter spectrometer and was designed to last more than three years in orbit. The early verification phase of the mission demonstrated that the instrument worked properly and that the cryogen consumption rate was low enough to ensure a mission lifetime exceeding 3 years. However, the liquid-He cryogen was completely vaporized two weeks after opening the dewar guard vacuum vent. The problem has been traced to inadequate venting of the dewar He and Ne gases out of the spacecraft and into space. In this paper we present the design and ground testing of the XRS instrument, and then describe the in-flight performance. An energy resolution of 6 eV was achieved during pre-launch tests and a resolution of 7 eV was obtained in orbit. The slight degradation is due to the effects of cosmic rays.

We present an analysis of Chandra X-ray observations of a compact group of galaxies, HCG 80 (z = 0.03). The system is a spiral-only group composed of four late-type galaxies, and has a high-velocity dispersion of 309 km s −1 . With high-sensitivity Chandra observations, we searched for diffuse X-ray emission from the intragroup medium (IGM); however, no significant emission was detected. We place a severe upper limit on the luminosity of the diffuse gas as L X < 6 × 10 40 erg s −1 . On the other hand, significant emission from three of the four members were detected. In particular, we discovered huge halo emission from HCG 80a that extends on a scale of ∼ 30 kpc perpendicular to the galactic disk, whose X-ray temperature and luminosity were measured to be ∼ 0.6 keV and ∼ 4 × 10 40 erg s −1 in the 0.5-2 keV band, respectively. It is most likely to be an outflow powered by intense starburst activity. Based on the results, we discuss possible reasons for the absence of diffuse X-ray emission in the HCG 80 group, suggesting that the system is subject to galaxy interactions, and is possibly at an early stage of IGM evolution.