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Several nearby clusters exhibit an excess of soft X-ray radiation that cannot be attributed to the hot virialized intracluster medium. There is no consensus to date on the origin of the excess emission: it could be either of thermal origin or due to an inverse Compton scattering of the cosmic microwave background. Using high-resolution XMM-Newton data of Sersic 159-03 we first show that strong soft excess emission is detected out to a radial distance of 0.9 Mpc. The data are interpreted using the two viable models available, i.e., by invoking either a warm reservoir of thermal gas or relativistic electrons that are part of a cosmic-ray population. The thermal interpretation of the excess emission, slightly favored by the goodness-of-fit analysis, indicates that the warm gas responsible for the emission is high in mass and low in metallicity.

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 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.

The Crab nebula and pulsar have been widely used as a calibration source for X-ray instruments. The in-flight effective area calibration of the Reflection Grating Spectrometers (RGS) of XMM-Newton depends upon the availability of reliable calibration sources. We analyse RGS observations of the Crab using different instrument configurations and spatial offsets, and make use of previous determinations of the continuum spectrum of the nebula plus pulsar. Due to the high spectral resolution of the RGS, we resolve the main absorption edges. We get an excellent fit to the Crab spectrum using this fixed continuum and the absorption spectrum determined by RGS. We get accurate column densities for the neutral atoms of H, N, O, Ne, Mg and Fe as well as a clear detection of Fe II and firm upper limits for other ions (O II, Mg II). We find solar-like abundances for N, O and Mg, and Fe (adding Fe I and Fe II), while Ne is overabundant. Finally, we show how we can determine the absolute flux of Crab with high accuracy by combining RGS and Chandra LETGS spectra of different sources.