We conducted a target of opportunity X-ray observation of the classical nova V458 Vulpeculae 88 days after the explosion using the Suzaku satellite. With a ∼20 ks exposure, the X-ray Imaging Spectrometer detected X-ray emission significantly harder than typical super-soft source emission. The X-ray spectrum shows Kα lines from N, Ne, Mg, Si, and S, and L-series emission from Fe in highly ionize...

We present Swift-UVOT data on the optical afterglow of the X-ray flash of 2005 April 6 (XRF 050406) from 88 s to ∼ 10 5 s after the initial prompt γ-ray emission. Our observations in the V, B and U bands are the earliest that have been taken of an XRF optical counterpart. Combining the early-time optical temporal and spectral properties with γ-and simultaneous X-ray data taken with the BAT and ...

We present an XMM-Newton observation of NGC 7469, including studies of the X-ray and UV variability, 0.2−10 keV spectral continuum, Fe Kα emission line and the first-ever high-resolution X-ray spectrum of the soft X-ray warm absorber. We compare the properties of this X-ray warm absorber with the UV warm absorber as seen in a FUSE observation one year previously. The 0.2−10 keV spectral continu...

From the group of galaxies HCG62, we detected an excess hard X-ray emission in energies above ∼ 4 keV with ASCA . The excess emission is spatially extended up to ∼ 10′ from the group center, and somewhat enhanced toward north. Its spectrum can be represented by either a power-law of photon index 0.8–2.7, or a Bremsstrahlung of temperature > 6.3 keV. In the 2–10 keV range, the observed hard X-ra...

Using soft x-ray observations of the bright new comet C/1999 S4 (LINEAR) with the Chandra x-ray observatory, we have detected x-ray line emission created by charge exchange between highly ionized solar wind minor ions and neutral gases in the comet's coma. The emission morphology was symmetrically crescent shaped and extended out to 300,000 kilometers from the nucleus. The emission spectrum con...

We consider the properties of soft X-ray emission lines in the reprocessed emission from a photoionized accretion disc. Observations of these lines will be important in determining the ionization state and metallicity of the innermost regions of active galaxies. Calculations of reflection from a constant-density disc with an ionization parameter, ξ, between 250 and 1000 erg cm s show that emiss...

The radio properties of hard (2-8 keV) X-ray selected sources are explored by combining a single 50 ks XMM-Newton pointing with the ultra-deep and homogeneous Phoenix radio (1.4GHz) survey (Hopkins et al. 2003). A total of 43 sources are detected above the X-ray flux limit fX(2−8 keV) = 7.7×10 −15 erg s cm, with 14 of them exhibiting radio emission above ≈ 40μJy (3σ). The X-ray/radio matched po...

The GALPROP model for cosmic-ray propagation is able to make explicit predictions for the distribution of galactic diffuse gamma-rays. We compare different propagation models with gamma-ray spectra measured by EGRET for various regions of the sky. This allows sensitive tests of alternative explanations for the apparent excess emission observed at GeV gamma-rays. We find that a population of har...

Three observational constraints can be placed on a warm-hot intergalactic medium (WHIM) using ROSAT PSPC pointed and survey data, the emission strength, the energy spectrum, and the fluctuation spectrum. The upper limit to the emission strength of the WHIM is 7.5 ± 1.0 keV s cm sr keV in the 3 4 keV band, an unknown portion of which value may be due to our own Galactic halo. The spectral shape ...

We report on a recent Chandra ACIS-S observation of the Circinus galaxy. These observations confirm that the nuclear spectrum results from reflection of a hard X-ray continuum by “neutral” matter. The nuclear X-ray emission is extended by ∼ 60 pc in the general direction of the optical “ionization cone”. An image in the Fe Kα line has been made and shows that this emission extends up to 200 pc ...