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Register a new userSoft X-ray Spectroscopy of NGC 1068 with XMM-Newton RGS and Chandra LETGS
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We present high-resolution soft-X-ray spectra of the prototypical Seyfert 2 galaxy, NGC 1068, taken with XMM-Newton RGS and Chandra LETGS. Its rich emission-line spectrum is dominated by recombination in a warm plasma (bright, narrow radiative recombination continua provide the ``smoking gun), which is photoionized by the inferred nuclear power-law continuum. Radiative decay following photoexcitation of resonant transitions is also significant. A self-consistent model of an irradiated cone of gas is capable of reproducing the hydrogenic/heliumlike ionic line series in detail. The radial ionic column densities we infer are consistent with absorption measurements (the warm absorber) in Seyfert 1 galaxies. This strongly suggests that the emission spectrum we observe from NGC 1068 emanates from its warm absorber. The observed extent of the ionization-cone/warm absorber in NGC 1068 of about 300 pc implies that a large fraction of the gas associated with generic warm absorbers may typically exist on the hundreds-of-parsec scale rather than much closer to the nucleus (e.g., less than a parsec). Spatially-resolved spectroscopy using the LETGS of two distinct emission regions yields two noticeably different spectra. We show that these differences are solely due to differing radial column densities. A fairly flat distribution in ionization parameter is necessary to explain the inferred radial ionic column densities of all spectra. This must primarily be due to a broad density distribution at each radius, spanning roughly 0.1-100 cm$^{-3}$. (Abridged)
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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. 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 (RRC) for several ions are also present, implying that most of the observed soft-X-ray emission arises in low-temperature (few eV) plasma. This plasma is photoionized by the inferred nuclear continuum (obscured along our line of sight), as in the unified model of active galactic nuclei (AGN). We find excess emission (compared with pure recombination) in all resonance lines (np to 1s) 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/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 ($xi=L_X/n_e r^2$) is necessary, spanning $logxi=0$--3. This suggests either radially-stratified ionization zones or the existence of a broad density distribution (spanning a few orders of magnitude) at each radius.
We report on a detailed study of the X-ray spectrum of the nearby eclipsing spectroscopic binary YY Gem. Observations were obtained simultaneously with both large X-ray observatories, XMM-Newton and Chandra. We compare the high-resolution spectra acquired with the Reflection Grating Spectrometer onboard XMM-Newton and with the Low Energy Transmission Grating Spectrometer onboard Chandra, and evidence in direct comparison the good performance of both instruments in terms of wavelength and flux calibration. The strongest lines in the X-ray spectrum of YY Gem are from oxygen. Oxygen line ratios indicate the presence of a low-temperature component (1-4 MK) with density n_e < 2 10^{10} cm^-3. The X-ray lightcurve reveals two flares and a dip corresponding to the secondary eclipse. An increase of the density during phases of high activity is suggested from time-resolved spectroscopy. Time-resolved global fitting of the European Photon Imaging Camera CCD spectrum traces the evolution of temperature and emission measure during the flares. These medium-resolution spectra show that temperatures > 10^7 K are relevant in the corona of YY Gem although not as dominant as the lower temperatures represented by the strongest lines in the high-resolution spectrum. Magnetic loops with length on the order of 10^9 cm, i.e., about 5 % of the radius of each star, are inferred from a comparison with a one-dimensional hydrodynamic model. This suggests that the flares did not erupt in the (presumably more extended) inter-binary magnetosphere but are related to one of the components of the binary.
We present results from Chandra HETGS (250 ks over two epochs) and XMM-Newton EPIC and RGS (60 ks) observations of NGC 2110, which has been historically classified as a Narrow Emission Line Galaxy galaxy. Our results support the interpretation that the source is a Seyfert 2 viewed through a patchy absorber. The nuclear X-ray spectrum of the source is best described by a power law of photon index $Gamma$ ~1.7, modified by absorption from multiple layers of neutral material at a large distance from the central supermassive black hole. We report the strong detections of Fe K$alpha$ and Si K$alpha$ lines, which are marginally resolved with the Chandra HETGS, and we constrain the emission radius of the fluorescing material to >1 pc. There is some evidence for modest additional broadening at the base of the narrow Fe K$alpha$ core with a velocity ~4500 km s$^{-1}$. We find tentative evidence for ionized emission (O VIII Ly $alpha$, an O VIII RRC feature, and possibly a Ne IX forbidden line) in the Chandra MEG and XMM-Newton RGS spectra, which could be associated with the known extended X-ray emission that lies ~160 pc from the nucleus. We suggest that the $10^{23}$ cm$^{-2}$ partially covering absorber originates in broad-line region clouds in the vicinity of the AGN, and that the $3times10^{22}$ cm$^{-2}$ coverer is likely to have a more distant origin and have a flattened geometry in order to allow the small-scale radio jet to escape.
We utilize the complimentary capabilities of XMM-Newton and Chandra, to conduct a detailed imaging and spectral study of the nearby galaxy NGC 4945 focussing on its nucleus and immediate surroundings (within ~1 kpc of the nucleus). A complex morphology is revealed including a predominantly hard, but partially resolved, nuclear source plus a spectrally soft, conically shaped X-ray plume, which extends 30 (500 pc) to the northwest. In NGC 4945 our direct view of the active galactic nucleus (AGN) is blocked below ~10 keV by extremely heavy line-of-sight absorption and the observed X-ray spectrum is dominated by multi-temperature thermal emission associated with the nuclear starburst and the X-ray plume. Nevertheless the signature of the AGN is present in the form of a neutral Compton reflection component and a 6.4 keV fluorescent iron Ka line. We conjecture that the site of the continuum reprocessing is the far wall of a highly inclined molecular torus, a geometry which is consistent with the presence of H2O megamaser emission in this source. The soft spectrum (~0.6 keV) and limb-brightened appearance of the X-ray plume suggest an interpretation in terms of a mass-loaded superwind emanating from the nuclear starburst.
First results from high-resolution coronal spectroscopy of flares with the Reflection Grating Spectrometers on board the textit{XMM-Newton} satellite are reviewed. Rotational modulation in the X-ray light curve of HR 1099 is discussed. Results from time-dependent spectroscopy of flares in the active stars HR 1099, AB Dor, YY Gem are also presented. Variations in the shape of the emission measure distributions, in the abundances and in the average density of the cool plasma are discussed.
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