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We fit the Doppler profiles of the He-like triplet complexes of O VII and N VI in the X-ray spectrum of the O star z Pup, using XMM-Newton RGS data collected over ~400 ks of exposure. We find that they cannot be well fit if the resonance and intercombination lines are constrained to have the same profile shape. However, a significantly better fit is achieved with a model incorporating the effects of resonance scattering, which causes the resonance line to become more symmetric than the intercombination line for a given characteristic continuum optical depth t*. We discuss the plausibility of this hypothesis, as well as its significance for our understanding of Doppler profiles of X-ray emission lines in O stars.

In a series of papers, Nicastro et al. have reported the detection of z > 0 O VII absorption features in the spectrum of Mrk 421 obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We evaluate this result in the context of a high-quality spectrum of the same source obtained with the Reflection Grating Spectrometer (RGS) on XMM-Newton. The data comprise over 955 ks of usable exposure time and more than 2.6 x 104 counts per 50 mA at 21.6 A. We concentrate on the spectrally clean region (21.3 < l < 22.5 ), where sharp features due to the astrophysically abundant O VII may reveal an intervening, warm-hot intergalactic medium (WHIM). We do not confirm detection of any of the intervening systems claimed to date. Rather, we detect only three unsurprising, astrophysically expected features down to the log(Ni) ~ 14.6 (3 s) sensitivity level. Each of the two purported WHIM features is rejected with a statistical confidence that exceeds that reported for its initial detection. While we cannot rule out the existence of fainter, WHIM related features in these spectra, we suggest that previous discovery claims were premature. A more recent paper by Williams et al. claims to have demonstrated that the RGS data we analyze here do not have the resolution or statistical quality required to confirm or deny the LETGS detections. We show that our analysis resolves the issues encountered by Williams et al. and recovers the full resolution and statistical quality of the RGS data. We highlight the differences between our analysis and those published by Williams et al. as this may explain our disparate conclusions.

We provide improved atomic calculation of wavelengths, oscillator strengths, and autoionization rates relevant to the 2 - 3 inner-shell transitions of Fe VI-XVI, the so-called Fe M-shell unresolved transition array (UTA). A second-order many-body perturbation theory is employed to obtain accurate transition wavelengths, which are systematically larger than previous theoretical results by 15-45 mA. For a few transitions of Fe XVI and Fe XV for which laboratory measurements exist, our new wavelengths are accurate to within a few mA. Using these new calculations, the apparent discrepancy in the velocities between the Fe M-shell UTA and other highly ionized absorption lines in the outflow of NGC 3783 disappears. The oscillator strengths in our new calculation agree well with the previous theoretical data, while the new autoionization rates are significantly larger, especially for lower charge states. We attribute this discrepancy to the missing autoionization channels in the previous calculation. The increased autoionization rates may slightly affect the column density analysis of the Fe M-shell UTA for sources with high column density and very low turbulent broadening. The complete set of atomic data is provided as an electronic table.

We present high-resolution laboratory spectra of K-shell X-ray lines from inner-shell excited and ionized ions of oxygen, obtained with a reflection grating spectrometer on the electron beam ion trap (EBIT-I) at the Lawrence Livermore National Laboratory. Only with a multi-ion model including all major atomic collisional and radiative processes are we able to identify the observed K-shell transitions of oxygen ions from O III to O VI. The wavelengths and associated errors for some of the strongest transitions are given, taking into account both the experimental and modeling uncertainties. The present data should be useful in identifying the absorption features present in astrophysical sources, such as active galactic nuclei and X-ray binaries. They are also useful in providing benchmarks for the testing of theoretical atomic structure calculations.

A long 280 ks observation of the Seyfert 1 galaxy NGC 3783 with XMM-Newton is reported. We focus on the oxygen line complex between 17 and 24 A as measured with the Reflection Grating Spectrometer. Accurate absorption column densities and emission-line fluxes are obtained. We explore several options for the geometry and physical form of the emitting and absorbing gas. The lack of change in ionization in the absorber despite an increase in continuum flux during the observation restricts the high-ionization (O-K) and the low-ionization (Fe-M) gas to distances of at least 0.5 and 2.8 pc, respectively, away from the central source. Given the P Cygni type profiles in the resonance spectral lines and the similar velocity widths, column densities, and ionization structure inferred separately from the emission and absorption lines, it is tempting to relate the X-ray narrow-line emitting plasma with the X-ray-absorbing gas. Under this assumption, the scenario of dense clumped clouds can be ruled out. Conversely, extended ionization cones (r [?] 10 pc) are consistent with the observation independent of this assumption. These findings are in stark contrast to the picture of numerous clumpy (ne [?] 109 cm-3) clouds drawn recently from UV spectra, but they are consistent with the extended X-ray emission cones observed directly in Seyfert 2 galaxies.

XMM-Newton RGS spectra of MCG -6-30-15 and Mrk 766 exhibit complex discrete structure, which was interpreted in a paper by Branduardi-Raymont and coworkers as evidence for the existence of relativistically broadened Lya emission from carbon, nitrogen, and oxygen, produced in the innermost regions of an accretion disk around a Kerr black hole. This suggestion was subsequently criticized in a paper by Lee and coworkers, who argued that for MCG -6-30-15, the Chandra HETG spectrum, which is partially overlapping the RGS in spectral coverage, is adequately fitted by a dusty warm absorber model, with no relativistic line emission. We present a reanalysis of the original RGS data sets in terms of the model by Lee and coworkers. Specifically, we show that (1) the explicit model given by Lee and coworkers differs markedly from the RGS data, especially at longer wavelengths, beyond the region sampled by the HETG; (2) generalizations of the Lee and coworkers model, with all parameters left free, do provide qualitatively better fits to the RGS data, but are still incompatible with the detailed spectral structure; (3) the ionized oxygen absorption-line equivalent widths are well measured with the RGS for both sources, and place very tight constraints on both the column densities and turbulent velocity widths of O VII and O VIII. The derived column densities are well below those posited by Lee and coworkers and are insufficient to play any role in explaining the observed edge-like feature near 17.5 A; (4) the lack of a significant neutral oxygen edge near 23 A places very strong limits on any possible contribution of absorption to the observed structure by dust embedded in a warm medium; and (5) the original relativistic line model with warm absorption proposed by Branduardi-Raymont and coworkers provides a superior fit to the RGS data, both in the overall shape of the spectrum and in the discrete absorption lines. We also discuss a possible theoretical interpretation for the putative relativistic Lya line emission in terms of the photoionized surface layers of the inner regions of an accretion disk. While there are still a number of outstanding theoretical questions about the viability of such a model, it is interesting to note that simple estimates of key parameters are roughly compatible with those derived from the observed spectra.

We present XMM-Newton observations of the luminous star e Carinae, including a high-resolution soft X-ray spectrum of the surrounding nebula obtained with the Reflection Grating Spectrometer (RGS). The European Photon Imaging Camera (EPIC) image of the field around e Car shows many early-type stars and diffuse emission from hot, shocked gas. The EPIC spectrum of the star is similar to that observed in previous X-ray observations and requires two temperature components. The RGS spectrum of the surrounding nebula shows K-shell emission lines from hydrogen- and helium-like nitrogen and neon and L-shell lines from iron but little or no emission from oxygen. The observed emission lines are not consistent with a single temperature, but the range of temperatures observed is not large, spanning ~0.15-0.6 keV. We obtain upper limits for oxygen line emission and derive a lower limit of N/O > 9. This is consistent with previous abundance determinations for the ejecta of e Car and with theoretical models for the evolution of massive, rotating stars.

We present the first high-resolution, soft X-ray spectrum of the prototypical Seyfert 2 galaxy, NGC 1068. This spectrum was obtained with the XMM-Newton Reflection Grating Spectrometer (RGS). Emission lines from H-like and He-like low-Z ions (from C to Si) and Fe L-shell ions dominate the spectrum. Strong, narrow radiative recombination continua (RRCs) for several ions are also present, implying that most of the observed soft X-ray emission arises in low-temperature plasma (kTe ~ a few eV). This plasma is photoionized by the inferred nuclear continuum (obscured along our line of sight), as expected in the unified model of active galactic nuclei (AGNs). We find excess emission (compared to pure recombination) in all resonance lines (1s-np) up to the photoelectric edge, demonstrating the importance of photoexcitation as well. We introduce a simple model of a cone of plasma irradiated by the nuclear continuum; the line emission we observe along our line of sight perpendicular to the cone is produced through recombination/radiative cascade following photoionization and radiative decay following photoexcitation. A remarkably good fit is obtained to the H-like and He-like ionic line series, with inferred radial ionic column densities consistent with recent observations of warm absorbers in Seyfert 1 galaxies. Previous Chandra imaging revealed a large (extending out to ~500 pc) ionization cone containing most of the X-ray flux, implying that the warm absorber in NGC 1068 is a large-scale outflow. To explain the ionic column densities, a broad, flat distribution in the logarithm of the ionization parameter (x = LX/ner2) is necessary, spanning log x = 0-3. This suggests either radially stratified ionization zones, the existence of a broad density distribution (spanning a few orders of magnitude) at each radius, or some combination of both.

A full set of calculations is presented for inner-shell n = 2-3 photoexcitation of the 16 iron charge states: Fe0+ (Fe I) through Fe15+ (Fe XVI). The blend of the numerous absorption lines arising from these excitations (mainly 2p-3d) forms an unresolved transition array (UTA), which has been recently identified as a prominent feature between 16 and 17 A in the soft X-ray spectra of active galactic nuclei (AGNs). Despite the blending within charge states, the ample separation between the individual-ion features enables precise diagnostics of the ionization range in the absorbing medium. Column density and turbulent velocity diagnostics are also possible, albeit to a lesser accuracy. An abbreviated set of atomic parameters useful for modeling the Fe 2p-3d UTA is given. It is shown that the effects of accompanying photoexcitation to higher levels (n [?] 4), as well as the associated photoionization edges, may also be relevant to AGN spectra.

We present a long-term multiwavelength light curve of Galactic black hole candidate GRS 1758-258 by combining previously published and archival data from Granat, ROSAT, the Compton Gamma Ray Observatory, the Rossi X-Ray Timing Explorer, BeppoSAX, ASCA, EXOSAT, and the Very Large Array. In addition, we include the first spectral results from the balloon-borne Gamma-Ray Arcminute Telescope Imaging System (GRATIS). In light of divergent analyses of the 1991-1993 ROSAT observations, we have reanalyzed these data; we find that the soft X-rays track the hard X-rays and that the fits require no blackbody component--indicating that GRS 1758-258 did not go to the high state in 1993. We offer an interpretation of these long-baseline data based on the advection-dominated accretion flow (ADAF) model for a system withimg1.gif [?] img1.gifcrit. We find that the 1990-1993 coeval hard and soft X-ray observations support the ADAF predictions. We discuss a new way to constrain black hole mass with spectral data and the ADAF theory and apply this technique to GRS 1758-258 to find M1 [?] 8-9 M at an assumed distance of 8.5 kpc. Further investigations of the ADAF model allow us to evaluate the model critically against the 1996 data and flux-flux diagram of Barret, McClintock, & Grindlay and to understand the limits of the latter's "X-ray burster box."

An analysis of the iron L-shell emission in the publicly available spectrum of the Capella binary system, as obtained by the High Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory, is presented. The atomic-state model, based on the HULLAC code, is shown to be especially adequate for analyzing high-resolution X-ray spectra of this sort. Almost all of the spectral lines in the 10-18 Å wavelength range are identified. It is shown that, for the most part, these lines can be attributed to emission from L-shell iron ions in the Capella coronae. Possibilities for electron temperature diagnostics using line ratios of Fe16+are demonstrated. It is shown that the observed iron-L spectrum can be reproduced almost entirely by assuming a single electron temperature of kTe= 600 eV. This temperature is consistent both with the measured fractional ion abundances of iron and with the temperature derived from ratios of Fe16+lines. A volume emission measure of 1053cm-3is calculated for the iron L-shell emitting regions of the Capella coronae, indicating a rather small volume of 1029cm3for the emitting plasma if an electron density of 1012cm-3is assumed.

An analysis of the iron L-shell emission in the publicly available spectrum of the Capella binary system, as obtained by the High Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory, is presented. The atomic-state model, based on the HULLAC code, is shown to be especially adequate for analyzing high-resolution X-ray spectra of this sort. Almost all of the spectral lines in the 10-18 A wavelength range are identified. It is shown that, for the most part, these lines can be attributed to emission from L-shell iron ions in the Capella coronae. Possibilities for electron temperature diagnostics using line ratios of Fe16+ are demonstrated. It is shown that the observed iron-L spectrum can be reproduced almost entirely by assuming a single electron temperature of kTe = 600 eV. This temperature is consistent both with the measured fractional ion abundances of iron and with the temperature derived from ratios of Fe16+ lines. A volume emission measure of 1053 cm-3 is calculated for the iron L-shell emitting regions of the Capella coronae, indicating a rather small volume of 1029 cm3 for the emitting plasma if an electron density of 1012 cm-3 is assumed.

We find resolved interstellar O K, Ne K, and Fe L absorption spectra in the Chandra X-Ray Observatory Low-Energy Transmission Grating Spectrometer (LETGS) spectrum of the low-mass X-ray binary X0614+091. We measure the column densities in O and Ne and find direct spectroscopic constraints on the chemical state of the interstellar O. These measurements probably probe a low-density line of sight through the Galaxy, and we discuss the results in the context of our knowledge of the properties of interstellar matter in regions between the spiral arms.