High-Resolution Spectroscopy from 3050 to 10000 A of the HDF-S QSO J2233-606 with UVES at the ESO VLT

We report on high-resolution observations ($\Re \simeq 45000$) of the Hubble Deep Field South QSO J2233-606 obtained with the VLT UV-Visual Echelle Spectrograph (UVES). We present spectral data for the wavelength region $3050 < \lambda < 10000$ \AA. The $S/N$ ratio of the final spectrum is about 50 per resolution element at 4000 \AA, 90 at 5000 \AA, 80 at 6000 \AA, 40 at 8000 \AA. Redshifts, column densities and Doppler widths of the absorption features have been determined with Voigt-profile fitting. A total of 621 lines have been measured. In particular 270 Ly-alpha lines, 41 Ly-beta and 24 systems containing metal lines have been identified. Together with other data in the literature, the present spectrum confirms that the evolution of the number density of Ly-alpha lines with $\log N($\huno$) > 14$ has an upturn at $z \sim 1.4-1.6$.Comment: 34 pages Latex, with 3 PostScript figures. Astronomical Journal, in press. A few revised upper limit

Deposing the Cool Corona of KPD 0005+5106

The ROSAT PSPC pulse height spectrum of the peculiar He-rich hot white dwarf KPD 0005+5106 provided a great surprise when first analysed by Fleming, Werner & Barstow (1993). It defied the best non-LTE modelling attempts in terms of photospheric emission from He-dominated atmospheres including C, N and O and was instead interpreted as the first evidence for a coronal plasma around a white dwarf. We show here that a recent high resolution Chandra LETGS spectrum has more structure than expected from a thermal bremsstrahlung continuum and lacks the narrow lines of H-like and He-like C expected from a coronal plasma. Moreover, a coronal model requires a total luminosity more than two orders of magnitude larger than that of the star itself. Instead, the observed 20-80 AA flux is consistent with photospheric models containing trace amounts of heavier elements such as Fe. The soft X-ray flux is highly sensitive to the adopted metal abundance and provides a metal abundance diagnostic. The weak X-ray emission at 1 keV announced by O'Dwyer et al (2003) instead cannot arise from the photosphere and requires alternative explanations. We echo earlier speculation that such emission arises in a shocked wind. Despite the presence of UV-optical O VIII lines from transitions between levels n=7-10, no X-ray O VIII Ly alpha flux is detected. We show that O VIII Lyman photons can be trapped by resonant scattering within the emitting plasma and destroyed by photoelectric absorption.Comment: 15 Pages, 4 figures. Accepted for the Astrophysical Journa

Radiative recombination data for modeling dynamic finite-density plasmas

We have calculated partial final-state resolved radiative recombination (RR) rate coefficients from the initial ground and metastable levels of all elements up to and including Zn, plus Kr, Mo, and Xe, for all isoelectronic sequences up to Na-like forming Mg-like. The data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf48, which spans a temperature range of z2(101-107) K, where z is the initial ion charge. Fits to total rate coefficients have been determined, for both the ground and metastable levels, and those for the ground are presented here. Comparison is made both with previous RR rate coefficients and with (background) R-matrix photoionization cross sections. This RR database complements a dielectronic recombination (DR) database already produced, and both are being used to produce updated ionization balances for both (electron) collisionally ionized and photoionized plasmas

Modeling of the Interaction of GRB Prompt Emission with the Circumburst Medium

We present methodology and results of numerical modeling of the interaction of GRB prompt emission with the circumburst medium using a modified version of the multi-group radiation hydrocode STELLA. The modification includes the nonstationary photoionization, the photoionization heating and the Compton heating along with the hydrodynamics and radiation transfer. The lightcurves and spectra of the outcoming gamma-ray, X-ray and optical emission are calculated for a set of models (shells) of the circumburst environment, which differ in dimensions, density, density profile, composition, temperature. In some cases total bolometric and optical luminosities can reach 10^47 and 10^43 erg/s respectively. These effects can be responsible for irregularities which are seen on lightcurves of some GRB's X-ray and optical afterglows.Comment: 27 pages, 16 colour figures, this version is translated by authors, so it differs from that, which is published in Astronomy Letter

Broad P V Absorption in the BALQSO, PG 1254+047: Column Densities, Ionizations and Metal Abundances in BAL Winds

This paper discusses the detection of P V 1118,1128 and other broad absorption lines (BALs) in archival HST spectra of the low-redshift BALQSO, PG 1254+047. The P V identification is secured by excellent redshift and profile coincidences with the other BALs, such as C IV 1548,1550 and Si IV 1393,1403, and by photoionization calculations showing that other lines near this wavelength, e.g. Fe III 1123, should be much weaker than P V. The observed BAL strengths imply that either 1) there are extreme abundance ratios such as [C/H] >~ +1.0, [Si/H] >~ +1.8 and [P/C] >~ +2.2, or 2) at least some of the lines are much more optically thick than they appear. I argue that the significant presence of P V absorption indicates severe line saturation, which is disguised in the observed (moderate-strength) BALs because the absorber does not fully cover the continuum source(s) along our line(s) of sight. Computed optical depths for all UV resonance lines show that the observed BALs are consistent with solar abundances if 1) the ionization parameter is at least moderately high, log U >~ -0.6, 2) the total hydrogen column density is log N_H(cm-2) >~ 22.0, and 3) the optical depths in strong lines like C IV and O VI 1032,1038 are >~25 and >~80, respectively. These optical depths and column densities are at least an order of magnitude larger than expected from the residual intensities in the BAL troughs, but they are consistent with the large absorbing columns derived from X-ray observations of BALQSOs. The outflowing BALR, at velocities from -15,000 to -27,000 km/s in PG 1254+047, is therefore a strong candidate for the X-ray absorber in BALQSOs.Comment: 16 pages (LaTeX) plus 8 pages of figures in one file (pg1254_figs.ps.gz), in press with Ap

XMM-Newton observations of the X-ray soft polar QS Telescopii

Context. On the basis of XMM-Newton observations, we investigate the energy balance of selected magnetic cataclysmic variables, which have shown an extreme soft-to-hard X-ray flux ratio in the ROSAT All-Sky Survey. Aims. We intend to establish the X-ray properties of the system components, their flux contributions, and the accretion geometry of the X-ray soft polar QS Tel. In the context of high-resolution X-ray analyses of magnetic cataclysmic variables, this study will contribute to better understanding the accretion processes on magnetic white dwarfs. Methods. During an intermediate high state of accretion of QS Tel, we have obtained 20 ks of XMM-Newton data, corresponding to more than two orbital periods, accompanied by simultaneous optical photometry and phase-resolved spectroscopy. We analyze the multi-wavelength spectra and light curves and compare them to former high- and low-state observations. Results. Soft emission at energies below 2 keV dominates the X-ray light curves. The complex double-peaked maxima are disrupted by a sharp dip in the very soft energy range (0.1-0.5 keV), where the count rate abruptly drops to zero. The EPIC spectra are described by a minimally absorbed black body at 20 eV and two partially absorbed MEKAL plasma models with temperatures around 0.2 and 3 keV. The black-body-like component arises from one mainly active, soft X-ray bright accretion region nearly facing the mass donor. Parts of the plasma emission might be attributed to the second, virtually inactive pole. High soft-to-hard X-ray flux ratios and hardness ratios demonstrate that the high-energy emission of QS Tel is substantially dominated by its X-ray soft component.Comment: Accepted for publication in Astronomy and Astrophysics. 7 pages, 4 figures, 2 table

Metal Abundances in the Magellanic Stream

We report on the first metallicity determination for gas in the Magellanic Stream, using archival HST GHRS data for the background targets Fairall 9, III Zw 2, and NGC 7469. For Fairall 9, using two subsequent HST revisits and new Parkes Multibeam Narrowband observations, we have unequivocally detected the MSI HI component of the Stream (near its head) in SII1250,1253 yielding a metallicity of [SII/H]=-0.55+/-0.06(r)+/-0.2(s), consistent with either an SMC or LMC origin and with the earlier upper limit set by Lu et al. (1994). We also detect the saturated SiII1260 line, but set only a lower limit of [SiII/H]>-1.5. We present serendipitous detections of the Stream, seen in MgII2796,2803 absorption with column densities of (0.5-1)x10^13 cm^-2 toward the Seyfert galaxies III Zw 2 and NGC 7469. These latter sightlines probe gas near the tip of the Stream (80 deg down-Stream of Fairall 9). For III Zw 2, the lack of an accurate HI column density and the uncertain MgIII ionization correction limits the degree to which we can constrain [Mg/H]; a lower limit of [MgII/HI]>-1.3 was found. For NGC 7469, an accurate HI column density determination exists, but the extant FOS spectrum limits the quality of the MgII column density determination, and we conclude that [MgII/HI]>-1.5. Ionization corrections associated with MgIII and HII suggest that the corresponding [Mg/H] may range lower by 0.3-1.0 dex. However, an upward revision of 0.5-1.0 dex would be expected under the assumption that the Stream exhibits a dust depletion pattern similar to that seen in the Magellanic Clouds. Remaining uncertainties do not allow us to differentiate between an LMC versus SMC origin to the Stream gas.Comment: 30 pages, 8 figures, LaTeX (aaspp4), also available at http://casa.colorado.edu/~bgibson/publications.html, accepted for publication in The Astronomical Journa

X-ray spectroscopy and photometry of the long-period polar AI Tri with XMM-Newton

Context. The energy balance of cataclysmic variables with strong magnetic fields is a central subject in understanding accretion processes on magnetic white dwarfs. With XMM-Newton, we perform a spectroscopic and photometric study of soft X-ray selected polars during their high states of accretion. Aims. On the basis of X-ray and optical observations of the magnetic cataclysmic variable AI Tri, we derive the properties of the spectral components, their flux contributions, and the physical structure of the accretion region in soft polars. Methods. We use multi-temperature approaches in our xspec modeling of the spectra to describe the physical conditions and the structures of the post-shock accretion flow and the accretion spot on the white-dwarf surface. In addition, we investigate the accretion geometry of the system by a timing analysis of the photometric data. Results. Flaring soft X-ray emission from the heated surface of the white dwarf dominates the X-ray flux during roughly 70% of the binary cycle. This component deviates from a single black body and can be described by a superimposition of mildly absorbed black bodies with a Gaussian temperature distribution. In addition, weaker hard X-ray emission is visible nearly all the time. The spectrum from the cooling post-shock accretion flow is most closely fitted by a combination of thermal plasma mekal models with temperature profiles adapted from prior stationary two-fluid hydrodynamic calculations. The soft X-ray light curves show a dip during the bright phase, which can be interpreted as self-absorption in the accretion stream. Phase-resolved spectral modeling supports the picture of one-pole accretion and self-eclipse. One of the optical light curves corresponds to an irregular mode of accretion. During a short XMM-Newton observation at the same epoch, the X-ray emission of the system is clearly dominated by the soft component.Comment: A&A, in press; 11 pages, 9 figures, 3 table

Chandra Phase-Resolved Spectroscopy of the Crab Pulsar

We present the first phase-resolved study of the X-ray spectral properties of the Crab Pulsar that covers all pulse phases. The superb angular resolution of the Chandra X-ray Observatory enables distinguishing the pulsar from the surrounding nebulosity, even at pulse minimum. Analysis of the pulse-averaged spectrum measures interstellar X-ray extinction due primarily to photoelectric absorption and secondarily to scattering by dust grains in the direction of the Crab Nebula. We confirm previous findings that the line-of-sight to the Crab is underabundant in oxygen, although more-so than recently measured. Using the abundances and cross sections from Wilms, Allen & McCray (2000) we find [O/H] = (3.33 +/-0.25) x 10**-4. Analysis of the spectrum as a function of pulse phase measures the low-energy X-ray spectral index even at pulse minimum -- albeit with large statistical uncertainty -- and we find marginal evidence for variations of the spectral index. The data are also used to set a new (3-sigma) upper limit to the temperature of the neutron star of log T(infinity) < 6.30.Comment: 20 Pages including 7 figures. Accepted for publication in the Astrophysical Journa