We present an exploratory Chandra ACIS-S3 study of the diffuse component of the cosmic X-ray background (CXB) in the 0.3-7 keV band for four directions at high Galactic latitudes, with emphasis on details of the ACIS instrumental background modeling. Observations of the dark Moon are used to model the detector background. A comparison of the Moon data and the data obtained with ACIS stowed outside the focal area showed that the dark Moon does not emit significantly in our band. Point sources down to 3 Â 10 À16 ergs s À1 cm À2 in the 0.5-2 keV band are excluded in our two deepest observations. We estimate the contribution of fainter, undetected sources to be less than 20% of the remaining CXB flux in this band in all four pointings. In the 0.3-1 keV band, the diffuse signal varies strongly from field to field and contributes between 55% and 90% of the total CXB signal. It is dominated by emission lines that can be modeled by a kT ¼ 0:1 0:4 keV plasma. In particular, the two fields located away from bright Galactic features show a prominent line blend at E % 580 eV (O vii+O viii) and a possible line feature at E $ 300 eV. The two pointings toward the North Polar Spur exhibit a brighter O blend and additional bright lines at 730-830 eV (Fe xvii). We measure the total 1-2 keV flux of 1:0 1:2 AE 0:2 ð Þ Â 10 À15 ergs s À1 cm À2 arcmin À2 (mostly resolved) and the 2-7 keV flux of 4:0 4:5 AE 1:5 ð Þ Â 10 À15 ergs s À1 cm À2 arcmin À2 . At E > 2 keV, the diffuse emission is consistent with zero, to an accuracy limited by the short Moon exposure and systematic uncertainties of the S3 background. Assuming Galactic or local origin of the line emission, we put an upper limit of $3 Â 10 À15 ergs s À1 cm À2 arcmin À2 on the 0.3-1 keV extragalactic diffuse flux.

We present the analysis of the X-ray Multi-Mirror Mission (XMM-Newton) European Photon Imaging Camera (EPIC) data of the Galactic supernova remnant (SNR) CTB 109 (G109.1-1.0). CTB 109 is associated with the anomalous X-ray pulsar (AXP) 1E 2259+586 and has an unusual semi-circular morphology in both the X-ray and the radio, and an extended X-ray bright interior region known as the 'Lobe'. The deep EPIC mosaic image of the remnant shows no emission towards the west where a giant molecular cloud complex is located. No morphological connection between the Lobe and the AXP is found. We find remarkably little spectral variation across the remnant given the large intensity variations. All spectra of the shell and the Lobe are well fitted by a single-temperature non-equilibrium ionization model for a collisional plasma with solar abundances (kT ≈ 0.5 − 0.7 keV, τ = n e dt ≈ 1 − 4 × 10 11 s cm −3 , N H ≈ 5 − 7 × 10 21 cm −2 ). There is no indication of nonthermal emission in the Lobe or the shell. We conclude that the Lobe originated from an interaction of the SNR shock wave with an interstellar cloud. Applying the Sedov solution for the undisturbed eastern part of the SNR, and assuming full equilibration between the electrons and ions behind the shock front, the SNR shock velocity is derived as v s = 720 ± 60 km s −1 , the remnant age as t = (8.8 ± 0.9) × 10 3 d 3 yr, the initial energy as E 0 = (7.4 ± 2.9) × 10 50 d 2.5 3 ergs, and the pre-shock density of the nuclei in the ambient medium as n 0 = (0.16 ± 0.02) d −0.5 3 cm −3 , at an assumed distance of D = 3.0 d 3 kpc. Assuming CTB 109 and 1E 2259+586 are associated, these values constrain the age and the environment of the progenitor of the SNR and the pulsar.

We present observations of the young, oxygen-rich supernova remnant 1E 0102.2-7219 taken by the Chandra X-Ray Observatory during its orbital activation and checkout phase. The boundary of the blast-wave shock is clearly seen for the first time, allowing the diameter of the remnant and the mean blast-wave velocity to be determined accurately. The prominent X-ray bright ring of material may be the result of the reverse shock encountering ejecta; the radial variation of O vii versus O viii emission indicates an ionizing shock propagating inward, possibly through a strong density gradient in the ejecta. We compare the X-ray emission with Australia Telescope Compact Array 6 cm radio observations (Amy & Ball) and with archival Hubble Space Telescope [O iii] observations. The ring of radio emission is predominantly inward of the outer blast wave, which is consistent with an interpretation of synchrotron radiation originating behind the blast wave but outward of the bright X-ray ring of emission. Many (but not all) of the prominent optical filaments are seen to correspond to X-ray bright regions. We obtain an upper limit of approximately 9x1033 ergs s-1 (3 sigma) on any potential pulsar X-ray emission from the central region.

The first observations conducted as part of the Chandra ACIS survey of M33 (ChASeM33) sampled the eclipsing X-ray binary M33 X-7 over a large part of the 3.45 day orbital period and have resolved eclipse ingress and egress for the first time. The occurrence of the X-ray eclipse allows us to determine an improved ephemeris of mid-eclipse and binary period as HJD (2; 453; 639:119 AE 0:005) AE N (3:453014 AE 0:000020) and constrain the eclipse half-angle to 26N5 AE 1N1. There are indications for a shortening of the orbital period. The X-ray spectrum is best described by a disk blackbody spectrum typical for black hole X-ray binaries in the Galaxy. We find a flat power density spectrum, and no significant regular pulsations were found in the frequency range of 10 À4 to 0.15 Hz. HST WFPC2 images resolve the optical counterpart, which can be identified as an O6 III star with the help of extinction and color corrections derived from the X-ray absorption. Based on the optical light curve, the mass of the compact object in the system most likely exceeds 9 M . This mass, the shape of the X-ray spectrum, and the short-term X-ray time variability identify M33 X-7 as the first eclipsing black hole high-mass X-ray binary.

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