XMM-Newton Reflection Grating Spectrometer Observations of Discrete Soft X-Ray Emission Features from NGC 1068

By A. Kinkhabwala, M. Sako, Eda Behar, S. Kahn, F. Paerels, A. Brinkman, J. Kaastra, M. Gu, D. Liedahl. 2002

267 citations recorded by the source corpus.

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 (ξ = LX/ner2) is necessary, spanning log ξ = 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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/8e4235ce3677a3d04aefcb453e4d5546edc87280

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Nuclear and High Energy Physics

Citations in the corpus

Revisiting the Unified Model of Active Galactic Nuclei (2015, methodology): “…NLRs supplemented by Chandra and XMM-Newton high resolution spectroscopy, clearly indicate X-ray line emission, mostly Ovii570 eV , that generally overlaps with the [O iii] bicone (Sako et al. 2000; Ogle et al. 2000; Kinkhabwala et al. 2002; Bianchi, Guainazzi & Chiaberge 2006; Wang et al. 2011a).”
On the origin of soft X-rays in obscured AGN: answers from high-resolution spectroscopy with XMM–Newton (2006, background): “High-resolution spectra unveiled signatures of photoionized plasma in a few bright objects: NGC 1068 (Kinkhabwala et al. 2002; Young et al. 2001), the Circinus Galaxy (Sambruna et al. 2001), Mkn 3 (Sako et al. 2000; Bianchi et al. 2005; Pounds et al. 2005); NGC 4151 (Schurch et al. 2004).”
The Parsec-Scale Radio Structure of NGC 1068 and the Nature of the Nuclear Radio Source (2004, methodology): “To quantify better the limits on the scattered light fraction in the soft X-ray band, we added and scaled the total (AGN continuum plus model S1 disk) spectrum that would be seen by the scattering mirror to the mean continuum level of the XMMNewton RGS spectrum of Kinkhabwala et al. (2002).”
X-ray spectral survey with XMM-Newton of a complete sample of nearby Seyfert galaxies (2005, methodology): “The XMM–Newton observation of this source was published by Kinkhabwala et al. (2002), who focused their analysis on the RGS study, and by Matt et al. (2004), who focused their analysis on the E > 4 keV data.”
An XMM-Newton hard X-ray survey of ultraluminous infrared galaxies (2003, background): “One possibility to explain it would be a reflected component by photoionized gas, as found for example in the type 2 Seyfert galaxy NGC 1068 (Kinkhabwala et al. 2002; Brinkman et al. 2002).”
X-ray obscuration and obscured AGN in the local universe (2005, background): “In a few bright, nearby Seyfert 2s, for which high resolution spectroscopic measurements have been possible (Sako et al. 2000, Sambruna et al. 2001, Kinkhabwala et al. 2002), soft X-rays are dominated by emission lines from highly ionized species due mainly to recombination and resonant scattering…”
The Ionized Gas and Nuclear Environment in NGC 3783. IV. Variability and Modeling of the 900 Kilosecond Chandra Spectrum (2003, background): “Kinkhabwala et al. (2002) revisited the thermal stability issue in NGC 1068 and showed that a wide range of Uox is needed to account for the observed X-ray emission lines.”
The nature and origin of Seyfert warm absorbers (2004, background): “So, the gas in the UV NLR (which has been associated with the X-ray NLR, e.g. Kinkhabwala et al. 2002) does appear to be an outflow, plausibly accelerated by radiation from the central engine.”
EVIDENCE FOR ULTRA-FAST OUTFLOWS IN RADIO-QUIET ACTIVE GALACTIC NUCLEI. II. DETAILED PHOTOIONIZATION MODELING OF Fe K-SHELL ABSORPTION LINES (2011, background): “ABSORPTION LINES Due to the intense X-ray luminosity of the central source, absorbers in the inner regions of AGNs are mainly photo-ionized by this radiation instead of being locally ionized by thermal collisions (e.g., Kinkhabwala et al. 2002; Crenshaw et al. 2003).”
The Compact, Conical, Accretion-Disk Warm Absorber of the Seyfert 1 Galaxy NGC 4051 and Its Implications for IGM-Galaxy Feedback Processes (2007, background): “Proposals span a factor > 106 in radius and include (a) the Narrow Line Region1(e.g. Kinkhabwala et al. 2002; Ogle et al. 2004), (b) the inner edge of the ‘obscuring torus’ (Krolik & Kriss 2001) , and (c) the accretion disk itself (Elvis 2000).”
The soft X-ray/NLR connection: a single photoionized medium? (2005, background): “This would imply a range in density and temperature at any given location, as already suggested, for exam- ple, by Kinkhabwala et al. (2002) and Ogle et al. (2003).”
Nuclear Activity in Nearby Galaxies (2008, background): “Starling et al. note that this may be a property unique to LINERs, as thermal gas in luminous Seyferts is usually photoionized rather than collisionally ionized (e.g., Kinkhabwala et al. 2002).”