Ehud Behar

XMM-Newton reflection grating spectrometer observations of discrete soft-x-ray emission features from NGC 1068

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, nar- row 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 (kTea few eV). This plasma is photoion- ized 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 cas- cade 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 distribu- tion in the logarithm of the ionization parameter (� ¼ LX=ner 2 ) is necessary, spanning log � ¼ 0-3. This sug- gests 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. Subject headings: galaxies: individual (NGC 1068) — galaxies: Seyfert — line: formation — X-rays: galaxies

High-Resolution X-Ray Spectroscopy and Modeling of the Absorbing and Emitting Outflow in NGC 3783

The high-resolution X-ray spectrum of NGC 3783 shows several dozen absorption lines and a few emission lines from the H-like and He-like ions of O, Ne, Mg, Si, and S, as well as from Fe XVII-Fe XXIII L-shell transitions. We have reanalyzed the Chandra HETGS spectrum using better flux and wavelength calibrations, along with more robust methods. Combining several lines from each element, we clearly demonstrate the existence of the absorption lines and determine that they are blueshifted relative to the systemic velocity by -610 ? 130 km s-1. We find the Ne absorption lines in the High-Energy Grating spectrum to be resolved with FWHM = 840 km s-1; no other lines are resolved. The emission lines are consistent with being at the systemic velocity. We have used regions in the spectrum where no lines are expected to determine the X-ray continuum, and we model the absorption and emission lines using photoionized-plasma calculations. The model consists of two absorption components, with different covering factors, which have an order-of-magnitude difference in their ionization parameters. The two components are spherically outflowing from the active galactic nucleus, and thus contribute to both the absorption and the emission via P Cygni profiles. The model also clearly requires O VII and O VIII absorption edges. The low-ionization component of our model can plausibly produce UV absorption lines with equivalent widths consistent with those observed from NGC 3783. However, we note that this result is highly sensitive to the unobservable UV to X-ray continuum, and the available UV and X-ray observations cannot firmly establish the relationship between the UV and X-ray absorbers. We find good agreement between the Chandra spectrum and simultaneous ASCA and RXTE observations. The 1 keV deficit previously found when modeling ASCA data probably arises from iron L-shell absorption lines not included in previous models. We also set an upper limit on the FWHM of the narrow Fe K? emission line of 3250 km s-1. This is consistent with this line originating outside the broad-line region, possibly from a torus.

High-Resolution Observations of the Elliptical Galaxy NGC 4636 with the Reflection Grating Spectrometer on Board XMM-Newton

We present the first high spectral resolution X-ray observation of the giant elliptical galaxy NGC 4636, obtained with the reflection grating spectrometer on board the XMM-Newton Observatory. The resulting spectrum contains a wealth of emission lines from various charge states of oxygen, neon, magnesium, and iron. Examination of the cross-dispersion profiles of several of these lines provides clear, unambiguous evidence of resonance scattering by the highest oscillator strength lines, as well as a weak temperature gradient in the inner regions of the interstellar medium. We invoke a sophisticated new Monte Carlo technique that allows us to properly account for these effects in performing quantitative fits to the spectrum. Our spectral fits are not subject to many of the systematics that have plagued earlier investigations. The derived metal abundances are higher than have usually been inferred from prior, lower spectral resolution observations of this source, but are still incompatible with conventional chemical-enrichment models of elliptical galaxies. In addition, our data are incompatible with standard cooling-flow models for this system; our derived upper limit to the mass deposition rate is below the predicted value by a factor of 3-5.

First light measurements with the XMM-Newton reflection grating spectrometers: Evidence for an inverse first ionisation potential effect and anomalous Ne abundance in the Coronae of HR 1099

The RS CVn binary system HR 1099 was extensively observed by the XMM-Newton observatory in February 2000 as its first-light target. A total of 570 ks of exposure time was accumulated with the Reflection Grating Spectrometers (RGS). The integrated X-ray spectrum between 5-38A is of unprecedented quality and shows numerous features attributed to transitions of the elements C, N, O, Ne, Mg, Si, S, Fe. Ni, and probably others. We perform an in-depth study of the elemental composition of the average corona of this system, and find that the elemental abundances strongly depend on the first ionisation potential (FIP) of the elements. But different from the solar coronal case, we find an inverse FIP effect, i.e., the abundances (relative to oxygen) increase with increasing FIP. Possible scenarios, e.g., selective enrichment due to Ne-rich flare-like events, are discussed.

Soft X-Ray Absorption by Fe0+ to Fe15+ in Active Galactic Nuclei

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.

X-ray spectroscopy of NGC 5548

We analyze the high-resolution X-ray spectrum of the Seyfert 1 galaxy NGC 5548, for the full 0:1{10 keV band, using improved calibration results of the Chandra-LETGS instrument. The warm absorber consists of at least three ionization components, with a low, medium and high ionization parameter. The X-ray absorbing material, from an outflowing wind, covers the full range of velocity components found from UV absorption lines. The presence of redshifted emission components for the strongest blue-shifted resonance absorption lines indicate that the absorber is located at a distance larger than the edge of the accretion disk. We derive an upper limit to the edge of the accretion disk of 1 light year. Absorption lines from ions of at least ten chemical elements have been detected, and in general there are no strong deviations from solar abundances. The narrow emission lines from the O vii and Ne ix forbidden and intercombination lines probably originate from much larger distances to the black hole. We nd evidence for weak relativistically broadened oxygen and nitrogen emission lines from the inner parts of the accretion disk, but at a much smaller flux level than those observed in some other active galactic nuclei. In addition, there is a broad, non-relativistic C vi Ly emission line that is consistent with emission lines from the inner part of the optical/UV broad line region.

The Chandra Iron-L X-Ray Line Spectrum of Capella

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.

Inner-Shell 1s-2p Soft X-Ray Absorption Lines

The HULLAC atomic code is used to compute wavelengths and oscillator strengths for the 1s-np inner-shell absorption lines in Li-like to F-like ions of neon, magnesium, aluminum, silicon, sulfur, argon, calcium, and iron. Many of these lines are expected to be observed in Chandra and XMM-Newton high-resolution X-ray spectra of active galaxies. The new atomic data are incorporated in the ION code for spectral modeling of photoionized plasmas. The calculated spectra are subsequently compared with the spectrum of NGC 3783 and show very good agreement. The usefulness of these lines as diagnostics for the ionization state, column densities, and velocities in line-of-sight photoionized gas is highlighted.

High-resolution X-ray spectroscopy of Procyon by Chandra and XMM-Newton

We report the analysis of the high-resolution soft X-ray spectrum of the nearby F-type star Procyon in the wavelength range from 5 to 175 A obtained with the Low Energy Transmission Grating Spectrometer (LETGS) on board Chandra and with the Reflection Grating Spectrometers (RGS) and the EPIC-MOS CCD spectrometers on board XMM-Newton. Line fluxes have been measured separately for the RGS and LETGS. Spectra have been tted globally to obtain self-consistent temperatures, emission measures, and abundances. The total volume emission measure is 4:1 10 50 cm 3 with a peak between 1 and 3 MK. No indications for a dominant hot component (T > 4 MK) were found. We present additional evidence for the lack of a solar-type FIP-eect, conrming earlier EUVE results.

The soft X-ray spectrum from NGC 1068 observed with LETGS on Chandra

Using the combined spectral and spatial resolving power of the Low Energy Transmission Grating (LETGS) on board Chandra, we obtain separate spectra from the bright central source of NGC 1068 (Primary region), and from a fainter bright spot 4”u2000to the NE (Secondary region). Both spectra are dominated by discrete line emission from H- and He-like ions of C through S, and from Fe L-shell ions, but also include narrow radiative recombination continua (RRC), indicating that most of the observed soft X-ray emission arises in low-temperature (kT_e ~ few eV) photoionized plasma. We confirm the conclusions of Kinkhabwala et al. ([CITE]), based on XMM-Newton Reflection Grating Spectrometer (RGS) observations, that the entire nuclear spectrum can be explained by recombination/radiative cascade following photoionization, and radiative decay following photoexcitation, with no evidence for the presence of hot, collisionally ionized plasma. In addition, we show that this same model also provides an excellent fit to the spectrum of the Secondary region, albeit with radial column densities roughly a factor of three lower, as would be expected given its distance from the source of the ionizing continuum. The remarkable overlap and kinematical agreement of the optical and X-ray line emission, coupled with the need for a distribution of ionization parameter to explain the X-ray spectra, collectively imply the presence of a distribution of densities (over a few orders of magnitude) at each radius in the ionization cone. Relative abundances of all elements are consistent with Solar abundance, except for N, which is 2–3 times Solar. Finally, the long wavelength spectrum beyond 30 Au2000is rich of L-shell transitions of Mg, Si, S, and Ar, and M-shell transitions of Fe. The velocity dispersion decreases with increasing ionization parameter, which has been deduced from the measured line intensities of particularly these long wavelength lines in conjunction with the Fe-L shell lines.