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The XMM-Newton view of Mrk 3 and IXO 30
Abstract
{{We present the analysis of the XMM-Newton European Photon Imaging Camera (EPIC) pn spectrum of the Seyfert 2 galaxy Mrk 3. We confirm that the source is dominated by a pure Compton reflection component and an iron K alpha line, both produced as a reflection from a Compton-thick torus, likely responsible also for the large column density (1.36(-0.04)(+0.03) x 10(24) cm(-2)) which is pierced by the primary power law only at high energies. A low inclination angle and an iron underabundance of a factor similar or equal to 0.82, suggested by the amount of reflection and the depth of the iron edge, are consistent with the iron K alpha line equivalent width with respect to the Compton reflection component, which is 610(-50)(+30) eV. Moreover, the iron linewidth
... Previously in X-ray spectral data fits (e.g. Bianchi et al. 2005), the assumed model for the zeroth-order continuum was an absorbed power law and the model for the scattered component was approximated by using simplistic models viz. reflection from infinite slab (Magdziarz & Zdziarski 1995). ...
Numerous X-ray spectral models have been developed to model emission reprocessed by the torus of an active galactic nucleus (AGN), e.g., UXCLUMPY, CTORUS, and MYTORUS. They span a range of assumed torus geometries and morphologies-some posit smooth gas distributions, and others posit distributions of clouds. It is suspected that given the quality of currently available data, certain model parameters, such as coronal power law photon index and parameters determining the morphology of the AGN torus, may be poorly constrained due to model degeneracies. In this work, we test the reliability of these models in terms of recovery of parameters and the ability to discern the morphology of the torus using XMM-Newton and NuSTAR spectral data. We perform extensive simulations of X-ray spectra of Compton-thick AGNs under six X-ray spectral models of the torus. We use Bayesian methods to investigate degeneracy between model parameters, distinguish models and determine the dependence of the parameter constraints on the instruments used. For typical exposure times and fluxes for nearby Compton-thick AGN, we find that several parameters across the models used here cannot be well constrained, e.g., the distribution of clouds, the number of clouds in the radial direction, even when the applied model is correct. We also find that Bayesian evidence values can robustly distinguish between a correct and a wrong model only if there is sufficient energy coverage and only if the intrinsic flux of the object is above a particular value determined by the instrument combination and the model considered.
... In obscured AGNs, the softest X-rays are typically dominated by scattered nuclear flux and diffuse plasma emission (e.g. Bianchi et al. 2005;Miniutti et al. 2007;Winter et al. 2008). In order to confirm that this is also the case in ESO 033-G002 as well, we extracted light curves in a variety of different energy bands. ...
We present the first high signal-to-noise broad-band X-ray spectrum of the radio-quiet type-2 Seyfert ESO 033-G002, combining data from XMM–Newton and NuSTAR. The nuclear X-ray spectrum is complex, showing evidence for both neutral and ionized absorption, as well as reflection from both the accretion disc and more distant material, but our broad-band coverage allows us to disentangle all of these different components. The total neutral column during this epoch is NH ∼ (5−6) × 1022 $\rm \, cm^{-2}$, consistent with the optical classification of ESO 033-G002 as a type-2 Seyfert but not so large as to prevent us from robustly determining the properties of the innermost accretion flow. The ionized absorption – dominated by lines from Fe xxv and Fe xxvi – reveals a moderately rapid outflow (vout ∼ 5400 $\rm \, km~s^{-1}$) which has a column comparable to the neutral absorption. We find the disc reflection from the innermost regions to be extreme, with a reflection fraction of Rfrac ∼ 5. This requires strong gravitational lightbending and, in turn, both an extremely compact corona (within ∼2 RG of the black hole) and a rapidly rotating black hole (a* > 0.96). Despite this tight size constraint, with a temperature of kTe = 40–70 keV the X-ray corona in ESO 033-G002 appears similar to other active galactic nucle in terms of its placement in the compactness–temperature plane, consistent with sitting close to the limit determined by runaway pair production. Finally, combining X-ray spectroscopy, timing, and updated optical spectroscopy, we also estimate the mass of the black hole to be log[MBH/M⊙] ∼ 7.0–7.5.
... Most of the previous works on Cases A, B, C, and D, both theoretical and observational, focused on the optical, ultraviolet, and infrared regimes (Menzel 1937;Menzel & Baker 1937;Chamberlain 1953;Soifer et al. 1981;Malkan & Sargent 1982;Hummer & Storey 1987;Keel & Windhorst 1991;Ferland 1999;Sánchez et al. 2007;Stelzer et al. 2012;Mennickent et al. 2016;Peimbert et al. 2017), with a small number of studies on X-rays - Storey & Hummer (1988, 1995 for one-electron ions and Porter & Ferland (2007) for two-electron ions. Some other previous studies on soft X-ray spectra are Paerels & Kahn (2003), Bianchi et al. (2005), Cappi et al. (2006), Guainazzi & Bianchi (2007), and Mao et al. (2018). Note that Kinkhabwala et al. (2002) have outlined many of the physical processes discussed in this paper, focusing on second-and third-row elements. ...
Future microcalorimeter X-ray observations will resolve spectral features in unmatched detail. Understanding of line formation processes in X-rays deserves much attention. The purpose of this paper is to discuss such processes in the presence of a photoionizing source. Line formation processes in one- and two-electron species are broadly categorized into four cases. Case A occurs when the Lyman line optical depths are very small and photoexcitation does not occur. Line photons escape the cloud without any scattering. Case B occurs when the Lyman line optical depths are large enough for photons to undergo multiple scatterings. Case C occurs when a broadband continuum source strikes an optically thin cloud. The Lyman lines are enhanced by induced radiative excitation of the atoms/ions by continuum photons, also known as continuum pumping. A fourth, less studied scenario, where the Case B spectrum is enhanced by continuum pumping, is called Case D. Here, we establish the mathematical foundation of Cases A, B, C, and D in an irradiated cloud with Cloudy. We also show the total X-ray emission spectrum for all four cases within the energy range 0.1–10 keV at the resolving power of XRISM around 6 keV. Additionally, we show that the combined effect of electron scattering and partial blockage of continuum pumping reduces the resonance line intensities. Such reduction increases with column density and can serve as an important tool to measure the column density/optical depth of the cloud.
... Most of the previous works on Case A, B, C, and D, both theoretical and observational, were focused on the optical, ultraviolet, and infrared regime (Menzel 1937;Menzel & Baker 1937;Chamberlain 1953;Soifer et al. 1981;Malkan & Sargent 1982;Hummer & Storey 1987;Keel & Windhorst 1991;Ferland 1999;Sánchez et al. 2007;Stelzer et al. 2012;Mennickent et al. 2016;Peimbert et al. 2017), with a small number of studies on the X-rays - Storey & Hummer (1988) and Storey & Hummer (1995) for oneelectron and Porter & Ferland (2007) for two-electron ions. Some other previous studies on soft X-ray spectrum are Paerels & Kahn (2003), Bianchi et al. (2005), Cappi et al. (2006), Guainazzi & Bianchi (2007), Mao et al. (2018). Note that, Kinkhabwala et al. (2002) outlined many of the physical processes discussed in this paper, focusing on second and third-row elements. ...
Future microcalorimeter X-ray observations will resolve spectral features in unmatched detail. Understanding the line formation processes in the X-rays deserves much attention. The purpose of this paper is to discuss such processes in the presence of a photoionizing source. Line formation processes in one and two-electron species are broadly categorized into four cases. Case A occurs when the Lyman line optical depths are very small and photoexcitation does not occur. Line photons escape the cloud without any scattering. Case B occurs when the Lyman-line optical depths are large enough for photons to undergo multiple scatterings. Case C occurs when a broadband continuum source strikes an optically thin cloud. The Lyman lines are enhanced by induced radiative excitation of the atoms/ions by continuum photons, also known as continuum pumping. A fourth less-studied scenario, where the Case B spectrum is enhanced by continuum pumping, is called Case D. Here, we establish the mathematical foundation of Cases A, B, C, and D in an irradiated cloud with Cloudy. We also show the total X-ray emission spectrum for all four cases within the energy range 0.1 - 10 keV at the resolving power of XRISM around 6 keV. Additionally, we show that a combined effect of electron scattering and partial blockage of continuum pumping reduces the resonance line intensities. Such reduction increases with column density and can serve as an important tool to measure the column density/optical depth of the cloud.
... The AGN nuclear emission can heat up its circumnuclear gas, and can result in narrow radiative recombination continua (RRC) as well as recombination lines of highly-ionised atomic species. This kind of photoionized spectra have been found in several sources, e.g., the Circinus Galaxy (Sambruna et al. 2001), Mrk 3 (Sako et al. 2000;Bianchi et al. 2005;Pounds & Page 2005), NGC 1068 (Kinkhabwala et al. 2002;Young et al. 2001), NGC 4151 (Schurch et al. 2004). In a XMM-Newton survey of obscured AGNs (Guainazzi & Bianchi 2007), photoionization signature was found in 36% of the sample. ...
We present a multi-epoch X-ray spectroscopy analysis of the nearby narrow-line Seyfert I galaxy NGC 5506. For the first time, spectra taken by Chandra, XMM-Newton, Suzaku, and NuSTAR - covering the 2000-2014 time span - are analyzed simultaneously, using state-of-the-art models to describe reprocessing of the primary continuum by optical thick matter in the AGN environment. The main goal of our study is determining the spin of the supermassive black hole (SMBH). The nuclear X-ray spectrum is photoelectrically absorbed by matter with column density $\simeq 3 \times 10^{22}$~cm$^{-2}$. A soft excess is present at energies lower than the photoelectric cut-off. Both photo-ionized and collisionally ionized components are required to fit it. This component is constant over the time-scales probed by our data. The spectrum at energies higher than 2 keV is variable. We propose that its evolution could be driven by flux-dependent changes in the geometry of the innermost regions of the accretion disk. If we take this hypothesis into account, the black hole spin in NGC 5506 is constrained to be comprised between $0.91<a<0.98$ at 90\% confidence level for one interesting parameter.
Numerous X-ray spectral models have been developed to model emission reprocessed by the torus of an active galactic nucleus (AGN), e.g. UXCLUMPY, CTORUS, MYTORUS. They span a range of assumed torus geometries and morphologies — some posit smooth gas distributions, and others posit distributions of clouds. It is suspected that given the quality of currently available data, certain model parameters, such as coronal power-law photon index and parameters determining the morphology of the AGN torus, may be poorly constrained due to model degeneracies. In this work, we test the reliability of these models in terms of recovery of parameters and the ability to discern the morphology of the torus using XMM-Newton and NuSTAR spectral data. We perform extensive simulations of X-ray spectra of Compton-thick AGNs under six X-ray spectral models of the torus. We use Bayesian methods to investigate degeneracy between model parameters, distinguish models and determine the dependence of the parameter constraints on the instruments used. For typical exposure times and fluxes for nearby Compton-thick AGN, we find that several parameters across the models used here cannot be well constrained, e.g. the distribution of clouds, the number of clouds in the radial direction, even when the applied model is correct. We also find that Bayesian evidence values can robustly distinguish between a correct and a wrong model only if there is sufficient energy coverage and only if the intrinsic flux of the object is above a particular value determined by the instrument combination and the model considered.
Context. The supergiant X-ray binary Vela X−1 represents one of the best astrophysical sources to investigate the wind environment of an O/B star irradiated by an accreting neutron star. Previous studies and hydrodynamic simulations of the system have revealed a clumpy environment and the presence of two wakes: an accretion wake surrounding the compact object and a photoionisation wake trailing it along the orbit.
Aims. Our goal is to conduct, for the first time, high-resolution spectroscopy on Chandra /HETGS data at the orbital phase φ orb ≈ 0.75, when the line of sight is crossing the photoionisation wake. We aim to conduct plasma diagnostics, inferring the structure and the geometry of the wind.
Methods. We performed a blind search employing a Bayesian block algorithm to find discrete spectral features and identify them thanks to the most recent laboratory results or through atomic databases. Plasma properties were inferred both with empirical techniques and with photoionisation models within CLOUDY and SPEX.
Results. We detect and identify five narrow radiative recombination continua (Mg XI-XII , Ne IX-X , O VIII ) and several emission lines from Fe, S, Si, Mg, Ne, Al, and Na, including four He-like triplets (S XV , Si XIII , Mg XI , and Ne IX ). Photoionisation models reproduce the overall spectrum well, except for the near-neutral fluorescence lines of Fe, S, and Si.
Conclusions. We conclude that the plasma is mainly photoionised, but more than one component is most likely present, which is consistent with a multi-phase plasma scenario, where denser and colder clumps of matter are embedded in the hot, photoionised wind of the companion star. Simulations with the future X-ray satellites Athena and XRISM show that a few hundred seconds of exposure is sufficient to disentangle the lines of the Fe K α doublet and the He-like Fe XXV , improving, in general, the determination of the plasma parameters.
We present a large compilation of reddening estimates from broad-line Balmer decrements for active galactic nuclei (AGNs) with measured X-ray column densities. The median reddening is E(B − V) ≈ 0.77 ± 0.10 for type-1 to type-1.9 AGNs with reported column densities. This is notably higher than the median reddening of AGNs from the SDSS. We attribute this to the selection bias of the SDSS towards blue AGNs. For other AGNs, we find evidence of a publication bias against reporting low column densities. We find a significant correlation between NH and E(B − V) but with a large scatter of ±1 dex. On average, the X-ray columns are consistent with those predicted from E(B − V) for a solar neighbourhood dust-to-gas ratio. We argue that the large scatter of column densities and reddenings can be explained by X-ray column density variability. For AGNs with detectable broad-line regions (BLRs) that have undergone significant changes of Seyfert type (‘changing-look’ AGNs), we do not find any statistically significant differences in NH or E(B − V) compared to standard type-1 to type-1.9 AGNs. There is no evidence for any type-1 AGNs being Compton thick. We also analyse type-2 AGNs and find no significant correlation between NH and narrow-line region reddening. We find no evidence for a previously claimed anticorrelation. The median column density of LINERs is 22.68 ± 0.75 compared to a column density of 22.90 ± 0.28 for type-2 AGNs. We find the majority of low column density type-2 AGNs are LINERs, but NH is probably underestimated because of scattered light.
We present the results obtained from a detailed X-ray timing and spectral analysis of Seyfert 2 galaxy NGC 6300 by using observations with the {\it Suzaku}, {\it Chandra} and {\it NuSTAR} observatories between 2007 and 2016. We calculate variance, rms fractional variability of the source in different energy bands and find variabilities in various energy bands. Spectral properties of the source are studied by using various phenomenological and physical models. The properties of the Compton clouds, reflection, Fe K$\alpha$ line emission and soft X-ray excess are studied in detail. Several physical parameters of the source are extracted and investigated to establish the presence/absence of any correlation between them. We also investigate the nature of the circumnuclear `torus' and find that the torus is not uniform, rather clumpy. The observed changes in the line-of-sight column density can be explained in terms of transiting clouds. The iron line emitting region is found to be different in the different epoch of observations. We also observe that the torus and the nucleus independently evolve over the years.
The observed spatial and kinematic overlap between soft X-ray emission and the Narrow Line Region (NLR) in obscured Active Galactic Nuclei (AGN) yields compelling evidence that relatively low-density gas co-exists with higher density gas on scales as large as 100s of pc. This is commonly interpreted as evidence for a constant gas pressure multiphase medium, likely produced by thermal instability. Alternatively, Radiation Pressure Compression (RPC) also leads to a density distribution, since a gas pressure (and hence density) gradient must arise within each cloud to counteract the incident ionising radiation pressure. RPC leads to a well-defined ionization distribution, and a Differential Emission Measure (DEM) distribution with a universal slope of ∼−0.9, weakly dependent on the gas properties and the illuminating radiation field. In contrast, a multiphase medium does not predict the form of the DEM. The observed DEMs of obscured AGN with XMM-Newton RGS spectra (the CHRESOS sample) are in striking agreement with the predicted RPC DEM, providing a clear signature that RPC is the dominant mechanism for the observed range of densities in the X-ray NLR. In contrast with the constant gas pressure multiphase medium, RPC further predicts an increasing gas pressure with decreasing ionization, which can be tested with future X-ray missions using density diagnostics.
We present a uniform broadband X-ray (0.5-100.0 keV) spectral analysis of 12 Swift/Burst Alert Telescope (BAT) selected Compton-thick ($\log N_{\mathrm{H}}/\mathrm{cm}^{-2} \geq 24$) Active Galactic Nuclei (CTAGNs) observed with Suzaku. The Suzaku data of 3 objects are published here for the first time. We fit the Suzaku and Swift spectra with models utilizing an analytic reflection code and those utilizing the Monte Carlo based model from an AGN torus by Ikeda et al. 2009. The main results are as follows. (1) The estimated intrinsic luminosity of a CTAGN strongly depends on the model; applying Compton scattering to the transmitted component in an analytic model may largely overestimates the intrinsic luminosity at large column densities. (2) Unabsorbed reflection components are commonly observed, suggesting that the tori are clumpy. (3) Most of CTAGNs show small scattering fractions (<0.5%) implying a buried AGN nature. (4) Comparison with the results obtained for Compton-thin AGNs (Kawamuro et al. 2016) suggests that the properties of these CTAGNs can be understood as a smooth extension from Compton-thin AGNs with heavier obscuration; we find no evidence that the bulk of the population of hard X-ray selected CTAGN is different from less obscured objects.
We study the prototypical Seyfert 2 galaxy, Markarian 3, based on imaging and high-resolution spectroscopy observations taken by the Chandra X-ray Observatory. We construct a deconvolved X-ray image, which reveals the S-shaped morphology of the hot gas in the narrow line region (NLR). While this morphology is similar to the radio and [O III] emission, the distribution of the X-ray gas is broader than that obtained at these other wavelengths. By mapping the density and temperature distribution of the hot gas in the NLR, we demonstrate the presence of shocks towards the west ($M=2.5^{+1.0}_{-0.6}$) and east ($M=1.5^{+1.0}_{-0.5}$). Moreover, we compute the flux ratios between the [O III] and $0.5-2$ keV band X-ray luminosity and show that it is non-uniform in the NLR with the western side of the NLR being more highly ionized. In addition, based on the Chandra grating data we investigate the line ratios of the Si XIII triplet, which are not consistent with pure photoionization. Based on these results, we suggest that in the NLR of Mrk 3 both photoionization and collisional ionization act as excitation mechanisms. We conclude that the canonical picture, in which photoionization is solely responsible for exciting the interstellar medium in the NLR of Seyfert galaxies, may be overly simplistic. Given that weak and small-scale radio jets are commonly detected in Seyfert galaxies, it is possible that shock heating plays a non-negligible role in the NLR of these galaxies.
We present the imaging and spectroscopic analysis of the combined Chandra ACIS-S observations of the Compton-thick Seyfert 2 galaxy NGC 4945. We performed a spatially-resolved spectroscopy of the circumnuclear environment of the source, picturing the innermost 200 parsecs around the highly absorbed nucleus. The additional 200 ks ACIS-S data with respect to the previous campaign allowed us to map with even greater detail the central structure of this source and to discover an enhanced iron emission in the innermost nuclear region, with respect to the associated Compton reflection continuum. We revealed that the Equivalent Width of the iron K$\alpha$ line is spatially variable (ranging from 0.5 to 3 keV), on scales of tens of parsecs, likely due to the ionization state and orientation effects of the reprocessing material, with respect to the central X-ray illuminating source. A clump of highly ionized Fe XXV He-$\alpha$ is also detected, 40 parsecs east to the nucleus. When observations taken years apart are considered, the central unresolved reflected emission is found to remain constant.
Fairall 9 is one of several type 1 active galactic nuclei for which it has been claimed that the angular momentum (or spin) of the supermassive black hole can be robustly measured, using the Fe K$\alpha$ emission line and Compton-reflection continuum in the X-ray spectrum. The method rests upon the interpretation of the Fe K$\alpha$ line profile and associated Compton-reflection continuum in terms of relativistic broadening in the strong gravity regime in the innermost regions of an accretion disc, within a few gravitational radii of the black hole. Here, we re-examine a Suzaku X-ray spectrum of Fairall 9 and show that a face-on toroidal X-ray reprocessor model involving only nonrelativistic and mundane physics provides an excellent fit to the data. The Fe K$\alpha$ line emission and Compton reflection continuum are calculated self-consistently, the iron abundance is solar, and an equatorial column density of $\sim 10^{24} \ \rm cm^{-2}$ is inferred. In this scenario, neither the Fe K$\alpha$ line, nor the Compton-reflection continuum provide any information on the black-hole spin. Whereas previous analyses have assumed an infinite column density for the distant-matter reprocessor, the shape of the reflection spectrum from matter with a finite column density eliminates the need for a relativistically broadened Fe K$\alpha$ line. We find a 90 per cent confidence range in the Fe K$\alpha$ line FWHM of $1895$-$6205 \ \rm km \ s^{-1}$, corresponding to a distance of $\sim 3100$ to $33,380$ gravitational radii from the black hole, or $0.015$-$0.49$ pc for a black-hole mass of $\sim 1-3 \times 10^{8} \ M_{\odot}$.
Orientation, together with accretion and evolution, is one of the three main drivers in the Grand Unification of Active Galactic
Nuclei (AGN). Being unresolved, determining the true inclination of those powerful sources is always difficult and indirect,
yet it remains a vital clue to apprehend the numerous, panchromatic and complex spectroscopic features we detect. There are
only a hundred inclinations derived so far; in this context, can we be sure that we measure the true orientation of AGN? To
answer this question, four methods to estimate the nuclear inclination of AGN are investigated and compared to inclination-dependent
observables (hydrogen column density, Balmer linewidth, optical polarization, and flux ratios within the IR and relative to
X-rays). Among these orientation indicators, the method developed by Fisher, Crenshaw, Kraemer et al., mapping and modeling
the radial velocities of the [O iii] emission region in AGN, is the most successful. The [O iii]-mapping technique shows highly statistically significant correlations at > 95% confidence level for rejecting null hypothesis
for all the test cases. Such results confirm that the Unified Model is correct at a scale ranging from kiloparsec to a fraction
of a parsec. However, at a radial distance less than 0.01 pc from the central black hole, warps and misalignments may change
this picture.
In this paper we report the results of an X-ray monitoring campaign on the heavily obscured Seyfert galaxy Markarian 3 carried
out between the fall of 2014 and the spring of 2015 with NuSTAR, Suzaku and XMM-Newton. The hard X-ray spectrum of Markarian 3 is variable on all the time scales probed by our campaign, down to a few days. The
observed continuum variability is due to an intrinsically variable primary continuum seen in transmission through a large,
but still Compton-thin column density (NH∼0.8-1.1× 1024 cm−2). If arranged in a spherical-toroidal geometry, the Compton scattering matter has an opening angle ≃66°, and is seen at a
grazing angle through its upper rim (inclination angle ≃70°). We report a possible occultation event during the 2014 campaign.
If the torus is constituted by a system of clouds sharing the same column density, this event allows us to constrain their
number (17 ± 5) and individual column density, [≃(4.9 ± 1.5) × 1022 cm−2]. The comparison of IR and X-ray spectroscopic results with state-of-the art “torus” models suggests that at least two thirds
of the X-ray obscuring gas volume might be located within the dust sublimation radius. We report also the discovery of an
ionized absorber, characterized by variable resonant absorption lines due to He- and H-like iron. This discovery lends support
to the idea that moderate column density absorbers could be due to clouds evaporated at the outer surface of the torus, possibly
accelerated by the radiation pressure due to the central AGN emission leaking through the patchy absorber.
Mkn 3 is a Seyfert 2 galaxy that is widely regarded as an exemplary
Compton-thick AGN. We study the Suzaku X-ray spectrum using models of the X-ray
reprocessor that self-consistently account for the Fe K$\alpha$ fluorescent
emission line and the associated Compton-scattered, or reflection, continuum.
We find a solution in which the average global column density,
$0.234^{+0.012}_{-0.010} \times 10^{24} \ \rm cm^{-2}$, is very different to
the line-of-sight column density, $0.902^{+0.012}_{-0.013} \times 10^{24} \ \rm
cm^{-2}$. The global column density is $\sim 5$ times smaller than that
required for the matter distribution to be Compton-thick. Our model accounts
for the profiles of the Fe K$\alpha$ and Fe K$\beta$ lines, and the Fe K edge
remarkably well, with a solar abundance of Fe. The matter distribution could
consist of a clumpy medium with a line-of-sight column density higher than the
global average. A uniform, spherically-symmetric distribution alone cannot
simultaneously produce the correct fluorescent line spectrum and reflection
continuum. Previous works on Mkn 3, and other AGN, that assumed a reflection
continuum from matter with an infinite column density could therefore lead to
erroneous or "puzzling" conclusions if the matter out of the line-of-sight is
really Compton-thin. Whereas studies of samples of AGN have generally only
probed the line-of-sight column density, with simplistic, one-dimensional
models, it is important now to establish the global column densities in AGN. It
is the global properties that affect the energy budget in terms of reprocessing
of X-rays into infrared emission, and that constrain population synthesis
models of the cosmic X-ray background.
We present an updated mid-infrared (MIR) versus X-ray correlation for the
local active galactic nuclei (AGN) population based on the high angular
resolution 12 and 18um continuum fluxes from the AGN subarcsecond MIR atlas and
2-10 keV and 14-195 keV data collected from the literature. We isolate a sample
of 152 objects with reliable AGN nature and multi-epoch X-ray data and minimal
MIR contribution from star formation. Although the sample is not homogeneous or
complete, we show that our results are unlikely to be affected by biases. The
MIR--X-ray correlation is nearly linear and within a factor of two independent
of the AGN type and the wavebands used. The observed scatter is <0.4 dex. A
possible flattening of the correlation slope at the highest luminosities probed
(~ 10^45 erg/s) is indicated but not significant. Unobscured objects have, on
average, an MIR--X-ray ratio that is only <= 0.15 dex higher than that of
obscured objects. Objects with intermediate X-ray column densities (22 < log
N_H < 23) actually show the highest MIR--X-ray ratio on average. Radio-loud
objects show a higher mean MIR--X-ray ratio at low luminosities, while the
ratio is lower than average at high luminosities. This may be explained by
synchrotron emission from the jet contributing to the MIR at low-luminosities
and additional X-ray emission at high luminosities. True Seyfert 2 candidates
and double AGN do not show any deviation from the general behaviour. Finally,
we show that the MIR--X-ray correlation can be used to verify the AGN nature of
uncertain objects. Specifically, we give equations that allow to determine the
intrinsic 2-10 keV luminosities and column densities for objects with complex
X-ray properties to within 0.34 dex. These techniques are applied to the
uncertain objects of the remaining AGN MIR atlas, demonstrating the usefulness
of the MIR--X-ray correlation as an empirical tool.
We present a spectral and imaging analysis of the XMM–Newton and Chandra observations of the Seyfert 2 galaxy ESO138-G001, with the aim of characterizing the circumnuclear material responsible for
the soft (0.3–2.0 keV) and hard (5–10 keV) X-ray emission. We confirm that the source is absorbed by Compton-thick gas. However,
if a self-consistent model of reprocessing from cold toroidal material is used (mytorus), a possible scenario requires the absorber to be inhomogenous, its column density along the line of sight being larger than
the average column density integrated over all lines of sight through the torus. The iron emission line may be produced by
moderately ionized iron (Fe xii-Fe xiii), as suggested by the shifted centroid energy and the low K β/K α flux ratio. The soft X-ray emission is dominated by emission
features, whose main excitation mechanism appears to be photoionization, as confirmed by line diagnostics and the use of self-consistent
models (cloudy).
Variability across the electromagnetic spectrum is a property of AGN that can
help constraining the physical properties of these galaxies. This is the third
of a serie of papers with the aim of studying the X-ray variability of
different families of AGN. The main purpose of this work is to investigate the
variability pattern in a sample of optically selected type 2 Seyfert galaxies.
We use the 26 Seyferts in the Veron-Cetty and Veron catalogue with data
available from Chandra and/or XMM-Newton public archives at different epochs,
with timescales ranging from a few hours to years. All the spectra of the same
source are simultaneously fitted and we let different parameters to vary in the
model. Whenever possible, short-term variations and/or long-term UV flux
variations are studied. We divide the sample in Compton-thick, Compton-thin,
and changing-look candidates. Short-term variability at X-rays is not found.
From the 25 analyzed sources, 11 show long-term variations; eight (out of 11)
are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look
candidates are also variable. The main driver for the X-ray changes is related
to the nuclear power (nine cases), while variations at soft energies or related
with absorbers at hard X-rays are less common, and in many cases these
variations are accompained with variations of the nuclear continuum. At UV
frequencies nuclear variations are nor found. We report for the first time two
changing-look candidates, MARK273 and NGC7319. A constant reflection component
located far away from the nucleus plus a variable nuclear continuum are able to
explain most of our results; the Compton-thick candidates are dominated by
reflection, which supresses their continuum making them seem fainter, and not
showing variations, while the Compton-thin and changing-look candidates show
variations.
We present far-infrared (FIR) and submillimetre photometry from the Herschel Space Observatory's Spectral and Photometric Imaging Receiver (SPIRE) for 313 nearby (z < 0.05) active galactic nuclei (AGN). We selected AGN from the 58 month Swift Burst Alert Telescope (BAT) catalogue, the result of an all-sky survey in the 14–195 keV energy band, allowing for a reduction
in AGN selection effects due to obscuration and host galaxy contamination. We find 46 per cent (143/313) of our sample is
detected at all three wavebands and combined with our Photoconductor Array Camera and Spectrometer (PACS) observations represents
the most complete FIR spectral energy distributions of local, moderate-luminosity AGN. We find no correlation among the 250,
350, and 500 μm luminosities with 14–195 keV luminosity, indicating the bulk of the FIR emission is not related to the AGN.
However, Seyfert 1s do show a very weak correlation with X-ray luminosity compared to Seyfert 2s and we discuss possible explanations.
We compare the SPIRE colours (F250/F350 and F350/F500) to a sample of normal star-forming galaxies, finding the two samples are statistically similar, especially after matching
in stellar mass. But a colour–colour plot reveals a fraction of the Herschel-BAT AGN are displaced from the normal star-forming galaxies due to excess 500 μm emission (E500). Our analysis shows E500 is strongly correlated with the 14–195 keV luminosity and 3.4/4.6 μm flux ratio, evidence the excess is related to the AGN.
We speculate these sources are experiencing millimetre excess emission originating in the corona of the accretion disc.
All galaxies beyond the Magellanic clouds with detected H2O maser emission so far are investigated and their X-ray observations are collected in detail to probe the X-ray properties of this special kind of galaxies. The soft excess and the strong iron emission line are commonly presented in their X-ray spectrum. Similar to the spectra of normal Seyfert 2 galaxies, the X-ray soft components are usually explained well by two alternative models or their combination: the absorbed power law model and the thermal emission model. The hard X-ray continua are usually flat, which should be caused by the increase of the reflection component, with the increase of the absorbing material density. Modeling their X-ray spectra shows that high absorbing column density is prevalent in our H2O megamaser host AGNs. Further, we investigate a possible relation between the iron line emission and the nuclear X-ray emission. It shows no significant correlation between the equivalent width (EW) of the neutral FeKα emission line (~ 6.4 keV) and the intrinsic nuclear X-ray luminosity. However, one trend appears clearly — the EW of the iron line decreases with the increase of the observed X-ray luminosity for our H2O maser galaxies. We also estimate the accretion rate of H2O maser host AGNs and the results show that maser galaxies may have a higher accretion rate than nonmaser Seyfert galaxies. In addition, possible relations between the EW of the iron line with the accretion rate and the central black hole mass are investigated and no significant trend of correlation can be found between them.
We report results from multi-epoch X-ray observations of the Seyfert 1.5 galaxy ESO 362−G18 performed between 2005 November
and 2010 June. ESO 362−G18 generally exhibits the typical X-ray spectrum of type 1 active galactic nuclei. A disc-reflection
component accounts for broad residuals in the iron K band and above 10 keV, as well as for a significant soft excess. From our best-fitting reflection model, we measure a black
hole spin a ≥ 0.92 at the 99.99 per cent confidence level. ESO 362−G18 is also (typically) mildly absorbed by a column of neutral gas.
The absorber is variable and one observation, performed ∼2 months after a typical mildly absorbed one, is heavily absorbed
by a cold column density of ∼ 3-4 × 1023 cm−2, nearly two orders of magnitude higher than that during any other observation. UV variability between the heavily absorbed
observation and the others suggests that the absorber can be identified with a dusty, clumpy torus. The absorption variability
time-scale enables us to locate the X-ray-emitting region within the innermost ∼50 gravitational radii. Such result holds
not only for the X-ray continuum, but also for the soft excess.
Active Galactic Nuclei (AGN) are axisymmetric systems to first order; their
observed properties are likely strong functions of inclination with respect to
our line of sight, yet the specific inclinations of all but a few AGN are
generally unknown. By determining the inclinations and geometries of nearby
Seyfert galaxies using the kinematics of their narrow-line regions (NLRs), and
comparing them with observed properties, we find strong correlations between
inclination and total hydrogen column density, infrared color, and H-beta
full-width at half maximum (FWHM). These correlations provide evidence that the
orientation of AGN with respect to our line of sight affects how we perceive
them, beyond the Seyfert type dichotomy. They can also be used to constrain 3D
models of AGN components such as the broad-line region and torus. Additionally,
we find weak correlations between AGN luminosity and several modeled NLR
parameters, which suggests that the NLR geometry and kinematics are dependent
to some degree on the AGN's radiation field.
We report results from multi-epoch X-ray observations of the polar-scattered
Seyfert 1 galaxy ESO 323-G77. The source exhibits remarkable spectral
variability from months to years timescales. The observed spectral variability
is entirely due to variations of the column density of a neutral absorber
towards the intrinsic nuclear continuum. The column density is generally
Compton-thin ranging from a few times 10$^{22}$ cm$^{-2}$ to a few times
10$^{23}$ cm$^{-2}$. However, one observation reveals a Compton-thick state
with column density of the order of 1.5 $\times$ 10$^{24}$ cm$^{-2}$. The
observed variability offers a rare opportunity to study the properties of the
X-ray absorber(s) in an active galaxy. We identify variable X-ray absorption
from two different components, namely (i) a clumpy torus whose individual
clumps have a density of $\leq$ 1.7 $\times$ 10$^8$ cm$^{-3}$ and an average
column density of $\sim$ 4 $\times$ 10$^{22}$ cm$^{-2}$, and (ii) the broad
line region (BLR), comprising individual clouds with density of 0.1-8 $\times$
10$^9$ cm$^{-3}$ and column density of 10$^{23}$-10$^{24}$ cm$^{-2}$. The
derived properties of the clumpy torus can also be used to estimate the torus
half-opening angle, which is of the order of 47 $^\circ$. We also confirm the
previously reported detection of two highly ionized warm absorbers with outflow
velocities of 1000-4000 km s$^{-1}$. The observed outflow velocities are
consistent with the Keplerian/escape velocity at the BLR. Hence, the warm
absorbers may be tentatively identified with the warm/hot inter-cloud medium
which ensures that the BLR clouds are in pressure equilibrium with their
surroundings. The BLR line-emitting clouds may well be the cold, dense clumps
of this outflow, whose warm/hot phase is likely more homogeneous, as suggested
by the lack of strong variability of the warm absorber(s) properties during our
monitoring.
We report on the X-ray observation of the Seyfert 1 galaxy ESO 323−G077 performed with XMM–Newton. The EPIC spectra show a complex spectrum with conspicuous absorption and emission features. The continuum emission can be
modelled with a power law with an index of 1.99 ± 0.02 in the whole XMM–Newton energy band, marginally consistent with typical values of type I objects. An absorption component with an uncommonly high
equivalent hydrogen column (nH= 5.82+0.12−0.11× 1022cm−2) is affecting the soft part of the spectrum. Additionally, two warm absorption components are also present in the spectrum.
The lower ionized one, mainly imprinting the soft band of the spectrum, has an ionization parameter of log U= 2.14+0.06−0.07 and an outflowing velocity of v= 3200+600−200 km s−1. Two absorption lines located at ∼6.7 and ∼7.0 keV can be modelled with the highly ionized absorber. The ionization parameter
and outflowing velocity of the gas measured are log U= 3.26+0.19−0.15 and v= 1700+600−400 km s−1, respectively. Four emission lines were also detected in the soft energy band. The most likely explanation for these emission
lines is that they are associated with an outflowing gas with a velocity of ∼2000 km s−1. The data suggest that the same gas which is causing the absorption could also being responsible of these emission features.
Finally, the XMM–Newton spectrum shows the presence of a relativistic iron emission line likely originated in the accretion disc of a Kerr black
hole with an inclination of ∼25°. We propose a model to explain the observed X-ray properties which invokes the presence of
a two-phase outflow with cone-like structure and a velocity of the order of 2000– 4000 km s−1. The inner layer of the cone would be less ionized, or even neutral, than the outer layer. The inclination angle of the source
would be lower than the opening angle of the outflowing cone.
We have studied the relationship between the [O iv] 25.89 mu m emission- line luminosities, obtained from Spitzer spectra, the X- ray continua in the 2Y10 keV band, primarily from ASCA, and the 14Y195 keV band obtained with the SWIFT Burst Alert Telescope ( BAT), for a sample of nearby ( z < 0: 08) Seyfert galaxies. For comparison, we have examined the relationship between the [ O iii] k5007, the 2Y10 keV, and the 14Y195 keV luminosities for the same set of objects. We find that both the [ O iv] and [ O iii] luminosities are well correlated with the BAT luminosities. When comparing [ O iv] and [ O iii] luminosities for the different types of galaxies, we find that the Seyfert 2s have significantly lower [ O iii] to [ Oiv] ratios than the Seyfert 1s. We suggest that this is due to more reddening of the narrowline region ( NLR) of the Seyfert 2s, since the [ O iv] 25.89 mu m emission line is much less affected by extinction. The combined effects of reddening and the X- ray absorption is the probable reason why the [ O iii] versus 2Y10 keV correlation is better than the [ O iv] versus 2Y10 kev correlation. Based on photoionization models, we find that the [ O iv] comes from higher ionization states and lower density regions than previous studies had determined for [ O iii]. Overall, we find the [ O iv] to be an accurate indicator of the power of the AGN.
The properties of a sample of extragalactic H2O maser sources over a wide spectral range are discussed. Based on a sample of 81 maser galaxies it is shown that mega- and
kilomasers have completely different properties. In particular, for megamasers the strongest observed relationships are between
the parameters of the H2O line and the mass of the galactic nucleus, while the parameters of the line are uncorrelated with the x-ray, infrared, and
radio emission. A weak correlation between megamaser emission and the surface (column) density of hydrogen is observed. As
for kilomasers, their H2O luminosity depends weakly on the x-ray emission, although in the case of soft x rays this dependence is significant. The
H2O luminosity of kilomasers is moderately correlated with the infrared and radio continuum luminosities, but the line parameters
are independent of the mass of the nucleus and the surface density of hydrogen.
We present a new XMM-Newton spectrum of the Seyfert 2 nucleus of IC 2560, which hosts H2O maser emission from an inclined Keplerian accretion disk. The X-ray spectrum shows soft excess due to multitemperature ionized plasma, a hard continuum, and strong emission features, from Mg, Si, S, Ca, Fe, and Ni, mainly due to fluorescence. It is consistent with reflection of the continuum from a mostly neutral medium and obscuration due to a high column density, >1024 cm-2. The amplitude of the reflected component may exceed 10% of the central unobscured luminosity. This is higher than the reflected fraction of a few percent observed in other Seyfert 2 sources such as NGC 4945. We observe an emission line at 6.7 keV, possibly due to Fe XXV, undetected in previous Chandra observations. The absorption column density associated with this line is less than 1023 cm-2, which is lower than the obscuration of the central source. We hypothesize that this highly ionized Fe line emission originates in warm gas, which is also responsible for a scattered component of continuum emission that may dominate the spectrum between 1 and 3 keV. We compare X-ray and maser emission characteristics of IC 2560 and other AGNs that exhibit water maser emission originating in disk structures around central engines. The temperature for the region of the disk associated with maser action is consistent with the expected 400-1000 K range. The clumpiness of disk structures (inferred from the maser distribution) may depend on the unobscured luminosities of the central engines.
We have analyzed spectra for all active galactic nuclei in the Rossi X-ray
Timing Explorer (RXTE) archive. We present long-term average values of
absorption, Fe line equivalent width, Compton reflection and photon index, as
well as calculating fluxes and luminosities in the 2-10 keV band for 100 AGN
with sufficient brightness and overall observation time to yield high quality
spectral results. We compare these parameters across the different
classifications of Seyferts and blazars. Our distributions of photon indices
for Seyfert 1's and 2's are consistent with the idea that Seyferts share a
common central engine, however our distributions of Compton reflection hump
strengths do not support the classical picture of absorption by a torus and
reflection off a Compton-thick disk with type depending only on inclination
angle. We conclude that a more complex reflecting geometry such as a combined
disk and torus or clumpy torus is likely a more accurate picture of the
Compton-thick material. We find that Compton reflection is present in ~85% of
Seyferts and by comparing Fe line EW's to Compton reflection hump strengths we
have found that on average 40% of the Fe line arises in Compton thick material,
however this ratio was not consistent from object to object and did not seem to
be dependent on optical classification.
We obtained a wide-band spectrum of the Compton-thick Seyfert2 galaxy
Mkn3 with Suzaku. The observed spectrum was clearly resolved into
weak, soft power-law emission, a heavily absorbed power-law component,
cold reflection, and many emission lines. The heavily absorbed
component, absorbed by gas with a column density of 1.1 ×
1024 cm-2, has an intrinsic 2-10keV luminosity of
˜1.6×1043 ergs-1, and is considered to
be direct emission from the Mkn3 nucleus. The reflection component was
interpreted as being the reflection of direct light off a cold, thick
material; the reflection fraction, R, was 1.36±0.20. The cold
material is inferred to be located > 1 pc from the central black
hole of Mkn3, due to the low ionization parameter of iron (xi <
1ergcms-1) and the narrow iron line width (σ <
22eV). The weak, soft power-law emission is considered to be scattered
light by ionized gas with a scattering fraction of 0.9±0.2%. The
existence of many highly ionized lines in the observed spectrum
indicates that the ionized gas has a broad ionized structure, with xi =
10--1000 erg cm s-1. This high-quality spectrum obtained by
Suzaku can be considered to be a template for studies of Seyfert2
galaxies.
Recent results, mainly from Chandra and XMM-Newton observations, on the
inner regions of AGN are reviewed. In particular, two topics are
discussed: the innermost regions of the accretion disc, as probed by
relativistic iron line features; and the obscured AGN, with particular
emphasis on the pc-scale torus.
Seyfert galaxies are a subclass of active galaxies and are categorized
as nearby, low luminosity, radio-quiet Active Galactic Nuclei (AGN)
hosted in spiral or lenticular galaxies. Demographically, Seyfert
galaxies may account for ~ 10% of the entire population of active
galaxies in the nearby universe. Seyfert galaxies are classified mainly
into two subclasses named as `type 1' and `type 2' Seyferts, based on
the presence and absence of broad permitted emission lines in their
optical spectra, respectively. Detection of broad permitted emission
lines in some Seyfert type 2s observed in the polarized light laid the
foundation of the Seyfert unification scheme, which hypothesizes that
Seyfert type 1s and type 2s belong to the same parent population and
appear different solely due to the differing orientations of the
obscuring material having a torus-like geometry around the AGN
(Antonucci and Miller 1985; Antonucci 1993).
The primary objective of this thesis work is to examine the validity and
limitations of the orientation and obscuration based Seyfert unification
scheme using multiwavelength (mainly X-ray and radio) observations. The
key issue in testing the Seyfert unification scheme has been acquiring a
well defined rigorously selected Seyfert sample. I have argued that the
Seyfert samples based on flux limited surveys at optical, IR, UV and
X-ray are likely to be biased against obscured and faint sources. In
order to test the predictions of Seyfert unification scheme I use a
sample based on properties (i.e., cosmological redshift, [OIII] emission
line luminosity, absolute bulge magnitude, absolute stellar magnitude of
the host galaxy and the Hubble stage of the host galaxy) that are
independent to the orientation of the obscuring torus, host galaxy and
the AGN axis. Furthermore, two Seyfert subtypes of our sample have
matched distributions in the orientation-independent properties and this
ensures the intrinsic similarity between two Seyfert subtypes within the
framework of the unification scheme. In other words, it is ensured that
the two subtypes being compared are not selected from entirely different
parts of the evolution function (redshift, luminosity, bulge magnitude,
stellar luminosity of the host galaxy and Hubble type of the host
galaxy).
To study the X-ray spectral properties of two Seyfert subtypes I use the
XMM-Newton pn data. The 0.5 - 10 keV X-ray spectra of
Seyfert galaxies are generally best fitted with a model consists of: an
absorbed power law with exponential cut-off which contains
cold absorption from the Galactic hydrogen column density together with
absorption from neutral gas at the redshift of the source; a narrow
Gaussian line fitted to the Fe K_alpha line at 6.4 keV; a
soft excess component characterized by either a steep power law and/or a
thermal plasma model with temperature kT and in some cases, reflection
component characterized by the reflection from an isotropically
illuminated cold slab, (model `pexrav' in XSPEC) is required. Partial
covering of the primary AGN power law component is also required for the
best fit in some sources. There are several type 2 sources in our sample
in which the hard (2.0 - 10.0 keV) part of the X-ray spectrum is best
fitted with a reflection component alone (`pexrav' model). The
statistical comparisons of the X-ray spectral properties show that in
compared to Seyfert type 1s, the type 2s exhibit lower X-ray
luminosities in soft (0.5 - 2.0 keV) and hard (2.0 -
10.0) X-ray bands, higher X-ray absorbing column densities, higher
equivalent widths of Fe K line, and lower flux ratios of hard
X-ray (2.0 - 10.0 keV) to [OIII]. In both the Seyfert subtypes, the
X-ray luminosity is moderately correlated with the pc-scale, kpc-scale
radio luminosities and [OIII] line luminosity, in a similar fashion. A
large fraction ~ 60 - 70% of type 2 Seyferts of our sample are likely to
be Compton-thick and as a case study of a Compton-thick AGN, we studied
the broad-band 0.5 - 50 keV X-ray spectral properties of NGC 5135 using
Suzaku (XIS and HID) data to unveil the nature and geometry of obscuring
torus.
To test the predictions of the Seyfert unification scheme in the radio
regime, I studied the radio properties of Seyfert galaxies using Giant
Meterwave Radio Telescope (GMRT) observations carried out at 240 MHz/610
MHz, and NRAO VLA Sky Survey observations at 1.4 GHz and VLA 5 GHz
observations from the literature. The four point (240 MHz, 610 MHz, 1.4
GHz, 5.0 GHz) integrated radio spectra of the two Seyfert subtypes are
similar and fairly steep (i.e., spectral index ~ -0.7). Radio luminosity
distributions at 240 MHz, 610 MHz, 1.4 GHz and 5.0 GHz are also similar
for the Seyfert type 1s and type 2s. The study on radio - IR luminosity
correlations shows that for both the Seyfert subtypes, the total 610 MHz
and 240 MHz radio luminosities are moderately correlated with near-IR,
mid-IR luminosities while the correlation becomes poorer with far-IR
luminosities. Furthermore, the 12 micron, 25 micron, 60 micron and 100
micron IR luminosity distributions are also statistically simil!
ar for the Seyfert type 1s and type 2s. I conclude that the statistical
comparisons of the X-ray, radio and IR properties of the two Seyfert
subtypes of our sample are consistent with the obscuration and
orientation based unification scheme.
We present the results of timing analysis of XMM-Newton observations of Seyfert 2 galaxies in order to search for differences in the mean properties of Seyfert 1 galaxies and Seyfert 2 galaxies. We selected 13 Seyfert 2 galaxies from the XMM-Newton archive that have hard X-ray components in their spectra and calculated the excess variance (σ) in the 2-10 keV band. We found that six Seyfert 2 galaxies (3C 98, IRAS 05189-2524, MCG -5-23-16, NGC 6300, UGC 4203, and PKS 1814-637) have buried luminous nuclei and that the nuclei have timing properties similar to those of Seyfert 1 nuclei. This indicates that these galaxies are candidates for having buried Seyfert 1 nuclei as expected by the unified Seyfert model. The first five galaxies show significant time variability. The amplitude of the time variability of IRAS 05189-2524 is similar to that of narrow-line Seyfert 1 galaxies. In contrast, the amplitude of variability of the seven other galaxies is quite small, much smaller than that of Seyfert 1 galaxies with similar X-ray luminosity. The lack of short time variability in these objects is explained by the dominance of the reflection component in three galaxies (Mrk 3, Mrk 463, and NGC 7582), and by the presence of very massive black holes and an inferred low accretion rate in the other three galaxies (NGC 1052, NGC 4507, and NGC 7172). For Mrk 348, the significant time variability that is expected based on the estimate of the central black hole mass was not detected.
We present the results of the simultaneous deep XMM-Newton and Chandra observations of the bright Seyfert 1.9 galaxy MCG -5-23-16, which is thought to have one of the best known examples of a relativistically broadened iron Kα line. The time-averaged spectral analysis shows that the iron K-shell complex is best modeled with an unresolved narrow emission component (FWHM < 5000 km s-1, EW ~ 60 eV) plus a broad component. This latter component has FWHM ~ 44,000 km s-1 and EW ~ 50 eV. Its profile is well described by an emission line originating from an accretion disk viewed with an inclination angle ~40°, with the emission arising from within a few tens of gravitational radii of the central black hole. The time-resolved spectral analysis of the XMM-Newton EPIC pn spectrum shows that both the narrow and broad components of the Fe K emission line appear to be constant in time within the errors. We detected a narrow sporadic absorption line at 7.7 keV, which appears to be variable on a timescale of 20 ks. If associated with Fe XXVI Lyα, this absorption is indicative of a possibly variable, high-ionization, high-velocity outflow. The variability of this absorption feature appears to rule out a local (z = 0) origin. The analysis of the XMM-Newton RGS spectrum reveals that the soft X-ray emission of MCG -5-23-16 is likely dominated by several emission lines superimposed on an unabsorbed scattered power-law continuum. The lack of strong Fe L-shell emission, together with the detection of a strong forbidden line in the O VII triplet, is consistent with a scenario in which the soft X-ray emission lines are produced in a plasma photoionized by the nuclear emission.
From the literature, we construct a sample of 25 Seyfert 2 galaxies (S2s) with a broad line region (BLR) detected in near infrared (NIR) spectroscopy and 29 with NIR BLRs which were not detected. We find no significant difference between the nuclei luminosity (extinction-corrected [OIII] 5007) and infrared color f60/f25 between the two populations, suggesting that the non-detections of NIR BLRs could not be due to low AGN luminosity or contamination from the host galaxy. As expected, we find significantly lower X-ray obscurations in Seyfert 2s with NIR BLR detection, supporting the unification scheme. However, such a scheme was challenged by the detection of NIR BLRs in heavily X-ray obscured sources, especially in six of them with Compton-thick X-ray obscuration. The discrepancy could be solved by the clumpy torus model and we propose a toy model demonstrating that IR-thin X-ray-thick S2s could be viewed at intermediate inclinations and compared with those IR-thick X-ray-thick S2s. We note that two of the IR-thin X-ray-thick S2s (NGC 1386 and NGC 7674) experienced X-ray transitions, i.e. from Compton-thin to Compton-thick appearance or vice versa based on previous X-ray observations, suggesting that X-ray transitions could be common in this special class of objects.
We aim at constraining the geometry of the reprocessing matter in the nearby
prototypical Seyfert 2 Galaxy Markarian 3 by studying the time evolution of
spectral components associated to the primary AGN emission and to its
Compton-scattering. We have analyzed archival spectroscopic observations of
Markarian 3 taken over the last 12 years with the XMM-Newton, Suzaku and Swift
observatories, as well as data taken during a monitoring campaign activated by
us in 2012. The timescale of the Compton-reflection component variability
(originally discovered by ASCA in the mid-'90s) is ~64 days. This upper limit
improves by more than a factor of 15 previous estimates of the
Compton-reflection variability timescale for this source. When the light curve
of the Compton-reflection continuum in the 4-5 keV band is correlated with the
15-150 keV Swift/BAT curve a delay ~1200 days is found. The cross-correlation
results are dependent on the model used to fit the spectra, although the
detection of the Compton-reflection component variability is independent of the
range of models employed to fit the data. Reanalysis of an archival Chandra
image of Markarian 3 indicates that the Compton-reflection and the Fe K-alpha
emitting regions are extended to the North up to ~300 pc. The combination of
these findings suggests that the optically-thick reprocessor in Markarian 3 is
clumpy. There is mounting experimental evidence for the structure of the
optically-thick gas and dust in the nuclear environment of nearby heavily
obscured AGN to be extended and complex. We discuss possible modifications to
the standard unification scenarios encompassing this complexity. Markarian 3,
exhibiting X-ray absorption and reprocessing on widely different spatial
scales, is an ideal laboratory to test these models (abridged).
We present monitoring analysis of 8 XMM-Newton observations of the Seyfert 2 galaxy Mrk 3, spanning a period of ∼19 months. The continuum flux in the 3–12 keV band remains constant during this observing period. The X-ray spectrum is well described, in agreement with previous works, by a highly absorbed (NH > 1024 cm–2) power law model, with a photon index Γ = 1.9 and a strong reflection component. A strong Fe Kα line at 6.4 keV with an equivalent width of ∼500 eV is detected in the X-ray spectrum. When we consider the co-added spectrum we also detect a weaker emission line at 7.4 keV corresponding to neutral Ni Kα emission and weak evidence for the presence of an ionized Fe Kα line at 6.7 keV. Direct comparison with the results obtained from an earlier XMM-Newton observation of Mrk 3, shows a decrease in the continuum flux of ∼30 per cent followed by a similar decrease in the reflected component. Both emission line components at 6.4 and 6.7 keV do not vary. However we find that an alternative model where the NH varies by 20 per cent is also plausible. In this case both the continuum and the reflected emission do not change. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
A spectral variability study of the two Narrow Line Seyfert 1 galaxies NGC 4051 and IRAS13224–3809 is presented. Both sources show a high degree of flux and spectral variability. The nuclear emission, lightly absorbed by warm material, has been decomposed into a direct power law emission and an ionized disc reflection plus constant emission from distant material. The ionized disc reflection component does not follow the variations of the primary component. Its flux is linearly correlated with the one of the power law component only at low fluxes, while it is almost constant at medium high-flux. This behavior is expected when the light bending effect is important. If so, most of the primary emission comes from only a few gravitational radii from the black hole. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
This paper reviews results obtained by the ESA observatory XMM-Newton in the field of Active Galactic Nuclei (AGN) research. I will cover six main areas: a) relativistic spectroscopy; b) soft excess; c) the quest for relativistic outflows; d) obscured AGN; e) scaling laws between Galactic and supermassive black holes, and f) AGN evolution and their contribution to the Cosmic X-ray Background.
We analysed the spectra from the XMM-Newton and the three longest Chandra observations of the Circinus Galaxy, the X-ray brightest, Compton-thick Seyfert 2 galaxy, to derive the physical and morphological parameters of the circumnuclear matter. We compare the line and continuum parameters with extensive calculations performed with the well-known photoionisation code CLOUDY. The line spectrum cannot be explained by a single zone, as three different reflecting regions are required. The first has low ionisation, accounting for the prominent iron K alpha line, and is likely to be identified with the "torus" envisaged in unification models for Seyfert galaxies; a lower limit of 0.05 pc to the distance of this matter from the nucleus has been estimated, using new constraints on the ionisation state of iron (<= FeX). The second zone is moderately ionised and optically thin (tau similar or equal to 0.2), and it accounts for the
We present a detailed analysis of the XMM-Newton Reflection Grating Spectrometer (RGS) high-resolution X-ray spectra of the Seyfert 2 galaxy, Mrk 573. This analysis is complemented by the study of the Chandra image and its comparison to optical (Hubble Space Telescope) and radio (Very Large Array) data. The soft X-ray emission is mainly due to gas photoionized by the central active galactic nucleus, as indicated by the detection of radiative recombination continua from O vii and O viii as well as by the prominence of the O vii forbidden line. This result is confirmed by the best fit obtained with a self-consistent cloudy photoionization model. However, a collisionally excited component is also required, in order to reproduce the Fe xvii lines, accounting for about one-third of the total luminosity in the 15-26 A band. Once the same model in the Chandra Advanced CCD Imaging Spectrometer (ACIS) data is adopted, another photoionized component, with a higher ionization parameter, is needed to take into account emission from higher Z metals. The broad-band ACIS spectrum also confirms the Compton-thick nature of the source. The imaging analysis shows the close morphological correspondence between the soft X-ray and the [O iii] emission. The radio emission appears much more compact, although clearly aligned with the narrow-line region. The collisional phase of the soft X-ray emission may be due to starburst, requiring a star formation rate of similar or equal to 5-9 M(circle dot) yr-1, but there is no clear evidence of this kind of activity from other wavelengths. On the other hand, it may be related to the radio ejecta, responsible for the heating of the plasma interacting with the outflow, but the estimated pressure of the hot gas is much larger than the pressure of the radio jets, assuming equipartition and under reasonable physical parameters.
We have performed a detailed analysis of the Chandra and Hubble Space Telescope (HST) images of the Seyfert 2 galaxy NGC 7582. The dust lane, as mapped by the HST near-infrared and optical images, strongly influences the morphology of the soft X-ray emission, being spatially coincident
with excess of X-ray absorption. Two ‘hotspots’, i.e. regions where emission from higher ionization stages of O and Ne is
stronger, are observed in the soft X-ray image. They can be tracers of variations of the ionization parameter, even if, at
least for one of them, absorption may be the dominant effect. The positions of the ‘hotspots’ suggest that they are not affected
by the star formation regions observed with HST, being located far away from them. Therefore the starburst does not seem to play an important role in the photoionization
of the soft X-ray emitting gas. The resulting picture is consistent with modified unification scenarios, where the Compton-thick
torus coexists with a large-scale Compton-thin material associated with the dust lane and circumnuclear gas is photoionized
by the active galactic nucleus along torus-free lines of sight.
We report results from the XMM–Newton observation of IRAS 13197−1627, a luminous infrared (IR) galaxy with a Seyfert 1.8 nucleus. The hard X-ray spectrum is steep
(Γ∼ 2.5) and is absorbed by Compton-thin (NH∼ 4 × 1023 cm−2) neutral gas. We detect a Fe Kα emission line at 6.4 keV, consistent with transmission through the absorber. The most striking
result of our spectral analysis is the detection of a dominant X-ray reflection component and broad Fe line from the inner
accretion disc. The reflection-dominated hard X-ray spectrum is confirmed by the strong Compton hump seen in a previous BeppoSAX observation and could be the sign that most of the primary X-rays are radiated from a compact corona (or base of the jet)
within a few gravitational radii from the black hole. We also detect a relatively strong absorption line at 6.81 keV which,
if interpreted as Fe xxv resonant absorption, implies an outflow with velocity ∼5 × 103 km s−1. In the soft energy band, the high-resolution gratings and the CCD-resolution data show the presence of both photoionized
gas and thermal plasma emission, the latter being most likely associated with a recent starburst of 15–20 M⊙ yr−1.
We revisit the relation between H2O maser detection rate and nuclear
obscuration for a sample of 114 Seyfert galaxies, drawn from the CfA, 12um and
IRAS F25/F60 catalogs. These sources have mid-infrared spectra from the Spitzer
Space Telescope and they are searched for X-ray and [O III], 5007Angstrom
fluxes from the literature. We use the strength of the [O IV], 25.9um emission
line as tracer for the intrinsic AGN strength. After normalization by [O IV]
the observed X-ray flux provides information about X-ray absorption. The
distribution of X-ray / [O IV] flux ratios is significantly different for
masers and non-masers: The maser detected Seyfert-2s (Sy 1.8-2.0) populate a
distinct X-ray / [O IV] range which is, on average, about a factor four lower
than the range of Seyfert-2 non-masers and about a factor of ten lower than the
range of Seyfert-1s (Sy 1.0-1.5). Non-masers are almost equally distributed
over the entire X-ray / [O IV] range. This provides evidence that high nuclear
obscuration plays a crucial role for the probability of maser detection.
Furthermore, after normalization with [O IV], we find a similar but weaker
trend for the distribution of the maser detection rate with the absorption of
the 7um dust continuum. This suggests that the obscuration of the 7 um
continuum occurs on larger spatial scales than that of the X-rays. Hence, in
the AGN unified model, at moderate deviation from edge-on, the 7um dust
absorption may occur without proportionate X-ray absorption. The absorption of
[O III] appears unrelated to maser detections. The failure to detect masers in
obscured AGN is most likely due to insufficient observational sensitivity.
Aims: The unification scheme of Seyfert galaxies predicts that the observed
differences between type 1 and type 2 Seyfert galaxies are solely due to the
differing orientations of the toroidal-shaped obscuring material around AGN.
The observed X-ray spectra of Seyfert type 2s compared to type 1s are expected
to be affected by higher absorbing column density due to the edge-on view of
the obscuring torus. We study the 0.5 - 10 keV X-ray spectral properties of
Seyfert type 1s and type 2s with the aim to test the predictions of Seyfert
unification scheme in the X-ray regime. Methods: We use an optically selected
Seyfert sample in which type 1s and type 2s have matched distributions in the
orientation independent parameters of AGN and host galaxy. Results: The 0.5 -
10 keV XMM-Newton pn X-ray spectra of Seyfert galaxies are in general best
fitted with a model consists of an absorbed power-law, a narrow Gaussian fitted
to the Fe K{\alpha} emission line and an often seen soft excess component
characterized by either a thermal plasma model with temperature kT \sim 0.1 -
1.0 keV and/or a steep power-law. The 2.0 - 10 keV hard X-ray continuum
emission in several Seyfert type 2s is reflection dominated and suggests the
Compton-thick obscuration. Results on the statistical comparison of the
distributions of the observed X-ray luminosities in the soft (0.5 - 2.0 keV)
and hard (2.0 - 10.0 keV) bands, the X-ray absorbing column densities, the
equivalent widths of Fe K{\alpha} line and the flux ratios of hard X-ray to
[OIII] {\lambda}5007{\AA} for the two Seyfert subtypes are consistent with the
obscuration and orientation based unification scheme.
We present the XMM-Newton RGS and EPIC pn spectra of a long (\simeq 100 ks) observation of one of the soft X-ray brightest Compton-thick Seyfert 2 galaxies, NGC 424. As a first step, we performed a phenomenological analysis of the data to derive the properties of all the spectral components. On the basis of these results, we fitted the spectra with self-consistent photoionisation models, produced with CLOUDY. The high-energy part of the spectrum is dominated by a pure neutral Compton reflection component and a neutral iron K-alpha line, together with K-alpha emission from neutral Ni, suggesting a significant Ni/Fe overabundance. The soft X-ray RGS spectrum comes mostly from line emission from H-like and He-like C, N, O, and Ne, as well as from the Fe L-shell. The presence of narrow RRC from O VIII, O VII, and C VI, the last two with resolved widths corresponding to temperatures around 5-10 eV, is a strong indication of a gas in photoionisation equilibrium, as confirmed by the prevalence of the forbidden component in the O VII triplet. Two gas phases with different ionisation parameters are needed to reproduce the spectrum with a self-consistent photoionisation model, any contribution from a gas in collisional equilibrium being no more than 10% of the total flux in the 0.35-1.55 keV band. When this self-consistent model is applied to the 0.5-10 keV band of the EPIC pn spectrum, a third photoionised phase is needed to account for emission lines with higher ionisation potential, although K-alpha emission from S XV and Fe XXVI remains under-predicted. Comment: 9 pages, 6 figures, accepted for publication in Astronomy and Astrophysics
We performed a blind search for narrow absorption features at energies greater than 6.4 keV in a sample of 42 radio-quiet AGNs observed with XMM-Newton. We detect 36 narrow absorption lines on a total of 101 XMM-Newton EPIC pn observations. The number of absorption lines at rest-frame energies E>7 keV is 22. Their global probability to be generated by random fluctuations is very low, less than 3x10^-8, and their detection have been independently confirmed by a spectral analysis of the MOS data, with associated random probability <10^-7. We identify the lines as Fe XXV and Fe XXVI K-shell resonant absorption. They are systematically blue-shifted, with a velocity distribution ranging from zero up to 0.3c, with a peak and mean value at 0.1c. We detect variability of the lines on both EWs and blue-shifted velocities among different observations even on time-scales as short as a few days, possibly suggesting somewhat compact absorbers. Moreover, we find no significant correlation between the cosmological red-shifts of the sources and the lines blue-shifted velocities, ruling out any systematic contamination by local absorption. If we define Ultra-fast Outflows (UFOs) those highly ionized absorbers with outflow velocities higher than 10^4 km/s, then the majority of the lines are consistent with being associated to UFOs and the fraction of objects with detected UFOs in the whole sample is at least 35%. This fraction is similar for Type 1 and Type 2 sources. The global covering fraction of the absorbers is consequently estimated to be in the range C=0.4-0.6, thereby implying large opening angles. These lines indicate that UFOs are a rather common phenomenon observable in the central regions of these sources and they are probably the direct signature of AGN accretion disk winds/ejecta. The detailed photo-ionization modeling of these absorbers is presented in a companion paper. Comment: 35 pages, accepted for publication in Astronomy & Astrophysics; corrected references
The physical conditions of the gas forming the narrow line regions (NLR) in active galactic nuclei (AGN) have been extensively studied in the optical band. We take advantage of the spectacular extension ($\sim$15") of the NLR in the type II Seyfert galaxy NGC 5252 and of the complementary characteristics of $XMM$--$Newton$ and $Chandra$ to investigate the physical conditions of the gas in this galaxy. The X-ray data from $XMM$--$Newton$ are used to define the spectral properties of the ionising nuclear source. The $Chandra$ data are used to trace the spatial characteristics of the soft X-ray emission. This information is then compared to the HST characteristics. The X-ray spectrum of the nucleus of NGC 5252 is intrinsically flat and absorbed by neutral gas with a column density N~10$^{22}$ cm$^{-2}$. Below 1 keV a soft excess is detected. The high-resolution spectrum obtained with the XMM-Newton RGS shows the presence, in the 0.2-1.5 keV range, of emission lines which strongly indicate that the soft X-ray component is due to ionised gas. Moreover, the soft X-ray emission is spatially resolved around and well overlaps the images obtained in narrow [OIII] optical band. The [OIII]/soft-X flux ratios along the ionisation cones is basically constant. This indicates that the electron density does not significantly deviates from the r$^{-2}$ law (constant ionisation parameter). This result combined with previous optical studies suggest two plausible but different scenarios in the reconstruction of the last 30000 years history of the central AGN. The most promising one is that the source is indeed a "quasar relic" with steady and inefficient energy release from the accretion of matter onto the central super-massive black-hole. This scenario is suggested also by the flat nuclear X-ray spectrum that suggests an advection dominate accretion flow (ADAF) like emission mechanism. Comment: Accepted for publication in A&A
We present a study of the resolved emission-line regions and an inner dust/gas disk in the Seyfert 2 galaxy Mrk 3, based on Hubble Space Telescope observations. We show that the extended narrow-line region (ENLR), spanning ~4 kpc, is defined by the intersection of the ionizing bicone of radiation from the AGN and the inner disk, which is not coplanar with the large-scale stellar disk. This intersection leads to different position and opening angles of the ENLR compared to the narrow-line region (NLR). A number of emission-line arcs in the ENLR appear to be continuations of dust lanes in the disk, supporting this geometry. The NLR, which consists of outflowing emission-line knots spanning the central ~650 pc, is in the shape of a backwards S. This shape may arise from rotation of the gas, or it may trace the original fueling flow close to the nucleus that was ionized after the AGN turned on. Comment: 22 page, 7 figures, accepted for publication in the Astronomical Journal
We present the results from ROSAT PSPC soft X-ray (0.1-2.0 keV)
observations of six Seyfert 2 galaxies, chosen from the brightest
Seyfert 2's detected with the Einstein Imaging Proportional Counter. All
of the targets were detected with the ROSAT PSPC. Spatial analysis shows
that the source density within a few arcminutes of each Seyfert 2 galaxy
is a factor of ˜8 higher than in the rest of the inner field of
view of the PSPC images. In NGC 1365 it appears that the serendipitous
sources may be X-ray binary systems in the host galaxy. The proximity of
the serendipitous sources, typically within a few arcminutes of the
target Seyfert 2, means that previous X-ray observations of the Seyfert
2 galaxies have been significantly contaminated, and that source
confusion is important on a spatial scale of ˜1'. Some spectra,
most notably Mrk 3 and NGC 1365, indicate the presence of a high
equivalent width soft X-ray line blend consistent with unresolved iron L
and oxygen K emission.
An observational review on H I in the Galaxy is presented. Attention is given to observations of interstellar atomic hydrogen from Lyman-alpha and the 21-cm line through indirect tracers such as dust and gamma rays; to what can be learned from such observations; to what the H I sky looks like; and to the state of knowledge in this area and the future prospects. Consideration is also given to results from recent H I investigations that bear on two important areas: the spatial organization of interstellar H I and its vertical distribution in the Galaxy.
The European Photon Imaging Camera (EPIC) consortium has provided the focal plane instruments for the three X-ray mirror systems on XMM-Newton. Two cameras with a reflecting grating spectrometer in the optical path are equipped with MOS type CCDs as focal plane detectors (Turner [CITE]), the telescope with the full photon flux operates the novel pn-CCD as an imaging X-ray spectrometer. The pn-CCD camera system was developed under the leadership of the Max-Planck-Institut für extraterrestrische Physik (MPE), Garching. The concept of the pn-CCD is described as well as the different operational modes of the camera system. The electrical, mechanical and thermal design of the focal plane and camera is briefly treated. The in-orbit performance is described in terms of energy resolution, quantum efficiency, time resolution, long term stability and charged particle background. Special emphasis is given to the radiation hardening of the devices and the measured and expected degradation due to radiation damage of ionizing particles in the first 9 months of in orbit operation.
The EPIC focal plane imaging spectrometers on XMM-Newton use CCDs to record the images and spectra of celestial X-ray sources focused by the three X-ray mirrors. There is one camera at the focus of each mirror; two of the cameras contain seven MOS CCDs, while the third uses twelve PN CCDs, defining a circular field of view of 30$^{\prime}$ diameter in each case. The CCDs were specially developed for EPIC, and combine high quality imaging with spectral resolution close to the Fano limit. A filter wheel carrying three kinds of X-ray transparent light blocking filter, a fully closed, and a fully open position, is fitted to each EPIC instrument. The CCDs are cooled passively and are under full closed loop thermal control. A radio-active source is fitted for internal calibration. Data are processed on-board to save telemetry by removing cosmic ray tracks, and generating X-ray event files; a variety of different instrument modes are available to increase the dynamic range of the instrument and to enable fast timing. The instruments were calibrated using laboratory X-ray beams, and synchrotron generated monochromatic X-ray beams before launch; in-orbit calibration makes use of a variety of celestial X-ray targets. The current calibration is better than 10% over the entire energy range of 0.2 to 10 keV. All three instruments survived launch and are performing nominally in orbit. In particular full field-of-view coverage is available, all electronic modes work, and the energy resolution is close to pre-launch values. Radiation damage is well within pre-launch predictions and does not yet impact on the energy resolution. The scientific results from EPIC amply fulfil pre-launch expectations.
A detailed analysis of the radiative and Auger de-excitation channels of K-shell vacancy states in Fe ii–Fe ix has been carried out. Level energies, wavelengths, $A$-values, Auger rates and fluorescence yields have been calculated for the lowest fine-structure levels populated by photoionization of the ground state of the parent ion. Different branching ratios, namely K$\alpha_2$/K$\alpha_1$, K$\beta$/K$\alpha$, KLM/KLL, KMM/KLL, and the total K-shell fluorescence yields, $\omega_{\rm K}$, obtained in the present work have been compared with other theoretical data and solid-state measurements, finding good general agreement with the latter. The K$\alpha_2$/K$\alpha_1$ ratio is found to be sensitive to the excitation mechanism. From these comparisons it has been possible to estimate an accuracy of ~10% for the present transition probabilities.
Results are presented from a study of soft X-ray spectra of 75 Seyfert galaxies observed by the Einstein Observatory IPC. The spectra in this sample (mostly high-luminosity Seyfert type 1s) are found to be consistent with a single power-law index alpha = 81. The AGN spectra observed with the IPC are compared with those from higher energy experiments, where AGN spectra have power law indices alpha = 0.7. It is found that the IPC spectra are systematically steeper than the HEAO 1 A-2 spectra of the same Seyfert galaxies, indicating a flattening toward higher energies.
We have used the ROSAT High Resolution Imager (HRI) to examine the distribution of soft X-rays in three nearby Seyfert galaxies with approximately 4 to 5 arcsecs FWHM spatial resolution. A feature of our analysis is an attempt to remove errors in the aspect solution using a method developed by one of us (J.M.). NGC 4151 shows resolved X-ray emission that is spatially correlated with the optical extended narrow-line region (ENLR), confirming the results obtained with the Einstein HRI by Elvis, Briel, & Henry. NGC 3516 is elongated along a position angle of approximately 40 to 220 deg, similar to the direction of the Z-shaped narrow-line region. MRK 3 is very faint in our HRI image and is probably spatially unresolved. We detect the faint X-ray source approximately 2 arcmins west of the MRK 3 nucleus previously found by Turner, Urry, & Mushotzky. We also detected the BL Lac object BL 1207 + 39 approximately 5 arcmins north-northwest of NGC 4151. This object appears spatially unresolved, but some excess X-ray emission may be observed in the azimuthally averaged radial brightness profile of BL 1207 + 39 between radii of 10 arcsecs and 30 arcsecs when compared to a calibration source. A much deeper image is necessary to confirm this result.
We present a detailed re-analysis of the two ASCA Performance Verification observations of the nearby Seyfert 1 galaxy MCG-6-30-15. Confirming the results of Fabian et al. (1994), we find definite evidence for the O vii and O viii K-shell absorption edges of the warm absorber and a doubling of the warm absorber column density within the 3 weeks separating the two observations. No intra-day flux-correlated variability of the warm absorber is found. However, we report the discovery of an `event' in which the warm absorber parameters temporarily change for ~10000 s before returning to their original values. Possible interpretations are discussed but a contradiction remains: the constancy of the ionization state of the warm absorber argues that it lies at large distances from the central source whereas the short term change in column density argues for small distances. Fluorescent iron emission is examined. As found by Fabian et al. (1994), the iron line is broad and strong ...
ROSAT, and now Chandra, X-ray images allow studies of extranuclear X-ray point sources in galaxies other than our own. X-ray observations of normal galaxies with ROSAT and Chandra have revealed that off-nuclear, compact, Intermediate-luminosity (Lx[2-10 keV] >= 1e39 erg/s) X-ray Objects (IXOs, a.k.a. ULXs [Ultraluminous X-ray sources]) are quite common. Here we present a catalog and finding charts for 87 IXOs in 54 galaxies, derived from all of the ROSAT HRI imaging data for galaxies with cz <= 5000 km/s from the Third Reference Catalog of Bright Galaxies (RC3). We have defined the cutoff Lx for IXOs so that it is well above the Eddington luminosity of a 1.4 Msun black hole (10^38.3 erg/s), so as not to confuse IXOs with ``normal'' black hole X-ray binaries. This catalog is intended to provide a baseline for follow-up work with Chandra and XMM, and with space- and ground-based survey work at wavelengths other than X-ray. We demonstrate that elliptical galaxies with IXOs have a larger number of IXOs per galaxy than non-elliptical galaxies with IXOs, and note that they are not likely to be merely high-mass X-ray binaries with beamed X-ray emission, as may be the case for IXOs in starburst galaxies. Approximately half of the IXOs with multiple observations show X-ray variability, and many (19) of the IXOs have faint optical counterparts in DSS optical B-band images. Follow-up observations of these objects should be helpful in identifying their nature. Comment: 29 pages, ApJS, accepted (catalog v2.0) (full resolution version of paper and future releases of catalog at http://www.xassist.org/ixocat_hri)
We report the detection of a narrow Fe-K emission line in the Seyfert 1 galaxy NGC 5548 with the Chandra High-Energy Transmission Gratings. In the galaxy frame we measure a center energy of 6.40 \pm 0.03 keV, a FWHM of 4515 (+3525,-2645) km/s, and an equivalent width of 133 (+62,-54) eV. The line energy is consistent with an origin in cold, neutral matter, but ionization states up to ~Fe XVIII are not ruled out. Assuming Keplerian motion, the velocity width is consistent with the line being produced in the outer optical/UV broad-line region (BLR) at about a light-month from the central X-ray source. We cannot rule out some contribution to the Fe-K line from a putative, parsec-scale obscuring torus. The continuum intensity during the Chandra observation was a factor ~2 less than typical historical levels. If the X-ray continuum was > than a factor 2 higher in the recent past before the Chandra observation and the narrow Fe-K line intensity had not yet responded, then the predicted line equivalent width and intensity for an origin in the BLR is within the 90% measurement errors. Retroactive spectral fitting of archival ASCA data shows evidence that the narrow Fe-K has a variable intensity. It will be important to measure the non-disk component of the Fe-K line in other AGN to obtain a more complete understanding of the total Fe-K line emission. Measurement of the narrow-line parameters provides powerful diagnostics of conditions beyond the accretion disk and is necessary to properly deconvolve the broad, relativistic Fe-K line. Comment: 35 pages including 3 figures. Latex file picks up figures. (Accepted for Publication in the Astrophysical Journal)
We present He-like line ratios (resonance, intercombination and forbidden lines) for totally and partially photoionized media. For solar plasmas, these line ratios are already widely used for density and temperature diagnostics of coronal (collisional) plasmas. In the case of totally and partially photoionized plasmas, He-like line ratios allow for the determination of the ionization processes involved in the plasma (photoionization with or without an additional collisional ionization process), as well as the density and the electronic temperature. With the new generation of X-ray satellites, Chandra/AXAF, XMM and Astro-E, it will be feasible to obtain both high spectral resolution and high sensitivity observations. Thus in the coming years, the ratios of these three components will be measurable for a large number of non-solar objects. In particular, these ratios could be applied to the Warm Absorber-Emitter, commonly present in Active Galactic Nuclei (AGN). A better understanding of the Warm Absorber connection to other regions (Broad Line Region, Narrow Line Region) in AGN (Seyferts type-1 and type-2, low- and high-redshift quasars...) will be an important key to obtaining strong constraints on unified schemes. We have calculated He-like line ratios, for Z=6, 7, 8, 10, 12 and 14, taking into account the upper level radiative cascades which we have computed for radiative and dielectronic recombinations and collisional excitation. The atomic data are tabulated over a wide range of temperatures in order to be used for interpreting a large variety of astrophysical plasmas. Comment: 23 pages, 11 figures, 14 tables. A&AS, in press
We present spatially resolved Chandra HETGS observations of the Seyfert 2 galaxy NGC 1068. X-ray imaging and high resolution spectroscopy are used to test the Seyfert unification theory. Fe K-alpha emission is concentrated in the nuclear region, as are neutral and ionized continuum reflection. This is consistent with reprocessing of emission from a luminous, hidden X-ray source by the obscuring molecular torus and X-ray narrow-line region (NLR). We detect extended hard X-ray emission surrounding the X-ray peak in the nuclear region, which may come from the outer portion of the torus. Detailed modeling of the spectrum of the X-ray NLR confirms that it is excited by photoionization and photoexcitation from the hidden X-ray source. K-shell emission lines from a large range of ionization states of H-like and He-like N, O, Ne, Mg, Al, Si, S, and Fe XVII-XXIV L-shell emission lines are modeled. The emission measure distribution indicates roughly equal masses at all observed ionization levels in the range log xi=1-3. We separately analyze the spectrum of an off-nuclear cloud. We find that it has a lower column density than the nuclear region, and is also photoionized. The nuclear X-ray NLR column density, optical depth, outflow velocity, and electron temperature are all consistent with values predicted by optical spectropolarimetry for the region which provides a scattered view of the hidden Seyfert 1 nucleus. Comment: 17 pages, 10 figures, accepted for publication in Astronomy and Astrophysics
We report on a dramatic flux (50 % increase in the LECS and MECS band) and spectral variation between two BeppoSAX observations of the Circinus Galaxy performed almost three years apart. Through the analysis of all Chandra observations available in the archive, including a new DDT observation on May 2001, we show that a high flux state of an extremely variable Ultra Luminous X-ray source (CG X-1: Bauer et al. 2001}, which is within the adopted BeppoSAX source extraction region of 2", is the most likely explanation for most of the observed variation. However, the presence of a high flux 6.7 keV line and the spectral variation of the PDS in the new BeppoSAX data could be partly due to intrinsic variation of the nucleus. Comparing the longest Chandra observation and the BeppoSAX one, we find that the long-term flux variability of CG X-1 is not accompanied by a significant spectral variability. We also re-analysed the Chandra HEG nuclear spectra and report on the presence of a Compton shoulder with a flux of about 20% the line core, in agreement with theoretical expectations for Compton-thick matter. Comment: 7 pages, 3 figures, accepted for publication on A&A
We present Rossi X-ray Timing Explorer monitoring observations of the type 2 Seyfert galaxy Markarian 3 spanning a 200-d period during which time the source flux
varied by a factor of ∼2 in the 4–20 keV bandpass. In broad agreement with earlier Ginga results, the average spectrum can be represented in terms of a simple spectral model consisting of a very hard power-law
continuum (Γ≈1.1) modified below ∼6 keV by a high absorbing column (NH∼6×1023 cm−2) together with a high equivalent width Fe K emission feature at 6.4 keV. The abnormally flat spectral index is probably the
signature of a strong reflection component and we consider two models incorporating such emission. In the first the reflected
signal suffers the same absorption as the intrinsic continuum, whereas in the second the reflection is treated as an unabsorbed
spectral component. In the former case, we require a very strong reflection signal (R≲3) in order to match the data; in addition variability of both the intrinsic power-law and the reflection components is required. The unabsorbed reflection model requires a somewhat higher
line-of-sight column density to the nuclear source (∼1024 cm−2), but in this case the reflected signal remains constant whilst the level of the intrinsic continuum varies. The latter description
is consistent with the reflection originating from the illuminated far inner wall of a molecular torus, the near side of which
screens our direct view of the central continuum source.
A new BeppoSAX broad-band (0.6-150 keV) spectrum of the Seyfert 2 galaxy Mkn 3 is presented. The spectrum provides a direct measurement of a large, neutral column of gas with Nh~10**24 cm**-2 in the source direction. The source, as bright as 3C 273 above 10 keV, has a steep (Gamma~1.8) spectrum without any evidence of a high-energy cutoff up to at least 150 keV. At lower energies, the data are best modeled with the addition of an unabsorbed reflection component. Combining these data with previous Ginga and ASCA observations, the Fe K$_{\alpha}$ and reflection continuum indicate that the reprocessed emission is responding slower than the intrinsic continuum variations suggesting a size of the reprocessor >= 2 pc. Identifying such a reprocessor with a (close to edge-on) obscuring torus, the overall result fits well into unified models since, presumably, one can interpret the strong absorption as due to transmission through the rim of the torus and the unabsorbed (directly viewed) reflection component as due to reprocessing from the torus inner surface.
Evidence is mounting that some Ultra-luminous X-ray sources (ULXs) may contain accreting intermediate-mass black holes (IMBHs). We review the current observational evidence for IMBH-ULXs. While low-luminosity ULXs with L_X <~ 10^39.5 erg/s (assuming isotropic emission) are consistent with mildly X-ray beamed high-mass X-ray binaries, there are a considerable number of ULXs with larger X-ray luminosities that are not easily explained by these models. Recent high-S/N XMM X-ray spectra are showing an increasing number of ULXs with ``cool disks'' -- accretion disks with multi-color blackbody inner disk temperatures kT_in ~ 0.1-0.2 keV, consistent with accreting IMBHs. Optical emission-line studies of ULX nebulae provide useful measurements of X-ray energetics, and can thus determine if the X-rays are emitted isotropically. Analysis of an optical spectrum of the Ho II ULX nebulae implies an X-ray energy source with ~10^40 erg/s is present, suggesting an isotropically-emitting IMBH. The spatial coincidence of ULXs with dense star clusters (young clusters and globular clusters) suggests that IMBHs formed in these clusters could be the compact objects in the associated ULXs. Quasi-periodic oscillations and frequency breaks in XMM power-density spectra of ULXs also suggest that the black hole masses are more consistent with IMBHs than stellar-mass black holes. Since _all_ of these ULXs with evidence for IMBHs are high-luminosity ULXs, i.e., L_X >~ 10^40 ergs, we suggest that this class of ULXs is generally powered by accreting IMBHs.
We present and discuss the high energy (E>4 keV) XMM-Newton spectrum of the Seyfert 2 galaxy, NGC 1068. Possible evidence for flux variability in both the neutral and ionized reflectors with respect to a BeppoSAX observation taken 3.5 years before is found. Several Fe and Ni emission lines, from both neutral and highly ionized material, are detected. The intensity of the iron K$\alpha$ Compton shoulder implies that the neutral reflector is Compton--thick, likely the visible inner wall of the $N_H > 10^{25}$ cm$^{-2}$ absorber. From the equivalent width of the ionized iron lines a column density of a few $\times 10^{21}$ cm$^{-2}$ is deduced for the hot ionized reflector. Finally, an iron (nickel) overabundance, when compared to solar values, of about 2 (4) with respect to lower Z elements, is found. Comment: accepted for publication in A&A
Inconsistencies in accepted values (in x units) of x-ray reference lines have recently been demonstrated, although all are supposedly based on "good" calcite crystals. Factors supporting the selection of the W Kα1 line as the X-Ray Wavelength Standard are critically discussed. A review is given of the experimental measurements which are used to establish the wavelength of this line on an absolute angstrom basis. Its value is λ W Kα1=(0.2090100±5 ppm) Å. This may be used to define a new unit, denoted by Å*, such that the W Kα1 wavelength is exactly 0.2090100 Å*; hence 1Å*=1ű5 ppm. The wavelengths of the Ag Kα1, Mo Kα1, Cu Kα1, and the Cr Kα2 have been established as secondary standards with probable error of approximately one part per million. Sixty-one additional x-ray lines have been used as reference values in a comprehensive review and reevaluation of more than 2700 emission and absorption wavelengths. The recommended wavelength values are listed in Å* units together with probable errors; corresponding energies are given in keV. A second table lists the wavelengths in numerical order, and likewise includes their energies in keV.
We present high signal-to-noise ratio spectropolarimetric observations
of 10 Seyfert 2 galaxies known to harbor obscured broad-line regions.
Most of the data, covering the spectral range λλ3200-7400
at moderate resolution, were obtained with the Kast double spectrograph
in combination with the CCD polarimeter on the Shane 3 m telescope at
Lick Observatory. Optical polarimetric imaging was also obtained with
the same telescope for one object (Mrk 463), and narrowband imaging
observations were made for four galaxies using the Nickel 1 m telescope.
We describe methods of data reduction and those used to correct the
polarimetry data for contamination from Galactic interstellar
polarization as well as dilution from unpolarized starlight in the
Seyfert host galaxies. From a comparison of various spectral properties,
we found that the hidden Seyfert 1 galaxies do not appear to differ
significantly from the normal Seyfert 1 galaxies, although the apparent
lack of Fe II emission in the polarized flux spectra of most of them is
intriguing.
This new, much enlarged catalogue has been made necessary by the
explosive growth of extragalactic astronomy over the last 15 years. With
data on more than 23,000 galaxies, it includes all galaxies with
apparent diameters larger than one arc minute, magnitudes brighter than
about magnitude 15.5, and redshifts not larger than 15,000 km/sec, as
well as many other objects of interest. Vol. I contains the explanations
and references, Vol. II and III contain the catalogue proper. The
catalogue gives for each galaxy its position, names, type and luminosity
class, optical diameter and axis ratio, position angle, optical,
infrared, and neutral hydrogen magnitudes, optical color indices and
surface brightnesses, neutral hydrogen indices and line widths, and
radial velocities.
Sixteen Seyfert galaxies, including 9 Seyfert 2 galaxies, were observed
with the Ginga satellite. Thirteen of the Seyfert galaxies in the sample
have been detected, and the Fe line and K-edge structure for these
galaxies investigated. Twelve of the 13 detected galaxies also have a
detected Fe line. The equivalent width of a Seyfert 1 galaxy is
distributed around a mean value of about 173 eV, with a standard
deviation of about 40 eV; that for a Seyfert 2 galaxy is scattered from
less than 80 eV to 1300 eV. Most of the detected galaxies show an
absorption feature at the energy of the iron K-edge. The iron column
density determined from the iron K-edge structure ranges from less than
10 to the 17.5th/sq cm to 2 x 10 to the 19th/sq cm. Using a Monte Carlo
simulation, it is found that isotropic X-ray emission within a uniformly
distributed gas cannot explain the observed result. The overall
distribution of the iron line and the K-edge intensity for all of the
galaxies in the sample could be reproduced by using an accretion torus
model with a single parameter: the viewing angle of the active galactic
nucleus within a accretion torus.
The reflection of the X-rays in K lines of heavy elements from a cold
surface is calculated. The radiative transfer is treated rigorously,
with the albedo in K lines expressed in terms of the H-function for
isotropic scattering. This approach is also applied to evaluate the
spectral shape of the low-energy wing of the line formed by the singly
scattered K photons. A detailed discussion is given of the main
characteristics of K-emission from the X-ray binaries. The prospects of
observations of the narrow K-alpha lines in X-ray binaries are analyzed,
with special attention paid to the information that can be obtained from
such observations. The minimum equivalent width which one could expect
in the case of the iron K-alpha line is evaluated for a number of
well-known X-ray binaries.
Spectropolarimetry was used to study eight high-polarization Seyfert 2
galaxies. In four of them (Mrk 3, Mrk 348, Mrk 463E, and NGC 7674),
evidence was found for a hidden broad-line region (BLR), visible only in
the polarized flux spectrum. The other four objects, Mrk 78, Mrk 1066,
NGC 591, and NGC 7672, may also have hidden BLRs, but at a flux level
below the detection threshold. The properties of the hidden BLRs are
consistent with their normal Seyfert 1 nuclei. If all Seyfert 2 galaxies
are in reality Seyfert 1 galaxies in which the nuclei are hidden from
direct view and seen only in scattered light, then one might expect that
many Seyfert 2 galaxies have polarizations of their featureless continua
greater than 50 percent. Such high polarization are not seen, perhaps
indicating a particular geometry, in which nearly edge-on obscuring tori
also block light from the scattering region. This model predicts that,
in edge-on cases, little or no featureless continua in the spectra of
the objects will be detected. Arguments are presented that objects with
high luminosity, such as QSOs, have geometrically thin tori and hence
are much less likely to have obscured continua and BLRs.
We present our analysis of the EXOSAT medium energy (ME) archival data
on dwarf novae. Many dwarf novae were observed with EXOSAT;
unfortunately, a significant fraction resulted in nondetection or
marginal detection with the ME instrument. Our analysis of the brightest
dwarf nova, SS Cyg, shows little correlation between the count rate and
the hardness ratio, contrary to an earlier report. This is likely to be
the result of a slight error in background subtraction performed. The
apparent lack of correlation favors a compact boundary layer between the
accretion disk and the white dwarf as the hard X-ray emitting region,
rather than an extended "corona." According to our spectral fit, all
dwarf nova data are compatible with a single temperature (2- > 20
keV) bremsstrahlung continuum with an iron emission line near 6.7 keV.
However, several sources show significant epoch-to-epoch variability,
the origin of which is poorly understood at the moment. Better hard
X-ray data are needed to advance our understanding of dwarf novae. With
this knowledge, we investigate the contribution of dwarf novae to the
Galactic ridge X-ray emission. They are found to be spectrally similar;
using a reasonable estimate of the spatial distribution of dwarf novae,
these systems appear to be a major, if not the dominant, component of
the ridge emission.
We calculate the intensities of the fluorescent and resonantly scattered
iron Kalpha lines in those active galactic nuclei (AGN) in which the
primary radiation at the line energy is completely blocked by
intervening matter along the line of sight (the so-called
`Compton-thick' Seyfert 2 galaxies). In the framework of unification
models for Seyfert galaxies, both a `cold' fluorescent line from the
obscuring torus and highly ionized lines from the warm material
responsible for the scattering and polarization of optical photons are
expected. The neutral iron line from the obscuring torus has an
equivalent width, with respect to the continuum reflected by the same
matter, of order 1-2 keV, provided that the matter is Compton thick. The
line emission from the warm material, in the optically thin regime for
all relevant processes, is dominated by the resonantly scattered lines.
However, for plausible physical conditions of this matter, the resonant
lines are likely to be optically thick in their centres. In this case,
the resonant line intensity can significantly decrease, and for
tau_T>~0.1 the fluorescent/recombination lines dominate the resonant
lines. We present analytical formulae for the equivalent widths of iron
lines in the optically thin case, and numerical results (obtained by
means of Monte Carlo simulations) for the optically thick case. We apply
the theoretical results to the most famous Compton-thick source, the
Seyfert 2 galaxy NGC 1068. The large uncertainties in the continuum
spectral shape and line equivalent widths prevent any definite
conclusions, but the application can be regarded as an example of how
the results presented in this paper could be used to estimate physical
and geometrical quantities in obscured AGN.
We have calculated the equivalent widths of the absorption lines produced by Fe xxv and Fe xxvi in a Compton-thin, low-velocity photoionized material illuminated by the nuclear continuum in active galactic nuclei. The results, plotted against the ionization parameter and the column density of the gas, are a complement to those presented by Bianchi & Matt for the emission lines from the same ionic species. As an extension to the work by Bianchi & Matt, we also present a qualitative discussion on the different contributions to the He-like iron emission line complex in the regimes where recombination or resonant scattering dominates, providing a useful diagnostic tool to measure the column density of the gas. Future high-resolution missions (e.g. Astro-E2) will allow us to fully take advantage of these plasma diagnostics. In the meantime, we compare our results with an up-to-date list of Compton-thick and unobscured (at least at the iron line energy) Seyfert galaxies with emission and/or absorption lines from H- and He-like iron observed with Chandra and XMM–Newton.
We present results from an XMM–Newton observation of the nearby Seyfert 2 galaxy NGC 5643. The nucleus exhibits a very flat X-ray continuum above 2 keV, together with a prominent Kα fluorescent iron line. This indicates heavy obscuration. We measure an absorbing column density NH in the range 6–10 × 1023 cm−2, either directly covering the nuclear emission, or covering its Compton reflection. In the latter case, we might be observing a rather unusual geometry for the absorber, whereby reflection from the inner far side of a torus is in turn obscured by its near side outer atmosphere. The nuclear emission might be then either covered by a Compton-thick absorber, or undergoing a transient state of low activity. A second source (christened ‘X-1’ in this paper) at the outskirts of the NGC 5643 optical surface outshines the nucleus in X-rays. If belonging to NGC 5643, it is the third brightest (LX∼ 4 × 1040 erg s−1) known ultraluminous X-ray source. Comparison with past large aperture spectra of NGC 5643 unveils dramatic X-ray spectral changes above 1 keV. We interpret these as due to variability of the active nucleus and of source X-1 intrinsic X-ray powers by factors of ≥10 and 5, respectively.
We calculate the equivalent width of the core, and the centroid energy and relative flux of the first-order Compton shoulder of the iron Kα emission line from neutral matter. The calculations are performed with Monte Carlo simulations. We explore a large range of column densities for both transmitted and reflected spectra, and study the dependence on the iron abundance. The Compton shoulder is now becoming observable in many objects thanks to the improved sensitivity and/or energy resolution of the XMM–Newton and Chandra satellites, and the present work aims to provide a tool to derive information on the geometry and element abundances of the line-emitting matter from Compton shoulder measurements.
A short Chandra ACIS-S observation of the Seyfert 2 galaxy IC 2560, which hosts a luminous nuclear water megamaser, shows (1) that the X-ray emission is extended; (2) that the X-ray spectrum displays emission features in the soft (E < 2 keV) X-ray band (this is the major component of the extended emission); and (3) a very strong (EW ∼ 3.6 keV) iron Kα line at 6.4 keV on a flat continuum. This last feature clearly indicates that the X-ray source is hidden behind Compton-thick obscuration, so that the intrinsic hard X-ray luminosity must be much higher than that observed, probably close to ∼3 × 1042 erg s−1. We briefly discuss the implications for powering of the maser emission and the central source.
I present the fundamental concepts of X-ray spectral formation in X-ray photoionized plasmas and transient plasmas, emphasizing the role of atomic kinetics in determining the attendant spectral characteristics.
Objects which harbor compact sites of hard X-ray production — active galactic nuclei, X-ray binaries, and cataclysmic variables — are the domains of photoionized plasmas. With a focus on the basic elements of discrete spectroscopy, I discuss the unique properties of X-ray spectra in such environments. As a prelude, an introduction to the theory of C,omptonization is provided, including a full derivation of the Kompaneets Equation, and its application to heating and cooling in X-ray nebulae. In the discussions on line spectroscopy, the mechanisms behind various plasma diagnostics are described, including recombination continua, Δn = 0 dielectronic recombination, density diagnostics, and Kα fluorescence.
The second topic of this chapter, the effect on X-ray spectra of time-dependent ionization conditions, is restricted to ionizing plasmas dominated by electron-ion impact processes. This scenario is motivated by impulsively heated plasmas, such as occur in supernova remnants and solar flares. Treated in this way, transient ionization is an extension of collisional ionization equilibrium. I present the fundamentals of ionization dynamics, followed by a numerical solution of the ionization equations for oxygen, a case study intended to illustrate the spectroscopic consequences of rapid ionization.
New abundance tables have been compiled for Cl chondrites and the solar photosphere and corona, based on a critical review of the literature to mid-1988. The meteorite data are generally accurate to ± 5–10%. Significant discrepancies between Sun and meteorites occur only for Fe, Mn, Ge, Pb, and W; other well-determined elements agree to ±9% on the average. There is no evidence for group fractionations in Cl chondrites of cosmochemically similar elements (refractories, siderophiles, volatiles, etc.), but a selective fractionation of Fe cannot be ruled out. Abundances of odd-A nuclides between A = 65 and 209 show a generally smooth trend, with elemental abundances conforming to the slope defined by isotopic abundances. Significant irregularities occur in the NdSmEu region, however, suggesting that the abundance curve is dependably smooth only down to the ∼20% level.
Seyfert galaxies are classified as type 1 or 2 according to the presence or absence of broad emission lines in the optical spectrum. The high velocities indicated by the broad lines in Seyfert 1 galaxies are taken to be good evidence of a compact, massive object, as are the strong and variable hard X-ray sources that are also generally observed in these objects. In contrast, Seyfert 2 galaxies possess neither of these characteristics, so the theory that they too have an accreting massive blackhole is less compelling. Since the discovery by spectropolarimetry of a 'hidden' Seyfert 1 nucleus in the prototypical Seyfert 2, NGC1068, the long-standing hope that the two classes may be unified has been revived. Here from observations by the Ginga satellite that another Seyfert 2, Mkn3, has the X-ray spectral signature of a hidden type 1 nucleus.
We report preliminary results of an ASCA observation of the Seyfert 2 galaxy Markarian 3 (Mkn 3). Comparison with previous Ginga and Broad-Band X-ray Telescope (BBXRT) observations shows that the observed hard X-ray luminosity above 4 keV decreased by a factor of approximately 3 (intrinsic luminosity by almost a factor of 6) in a period of approximately 3.6 yr. On the other hand, the soft luminosity has not varied significantly in approximately 13 yr, lending support to the extended nature of the soft emission, perhaps dominated by scattering of the nuclear X-rays. ASCA resolves the Fe K line emission into at least two components for the first time. The dominant component at 6.4 keV has an equivalent width of approximately 860 eV and full width at half maximum (FWHM) approximately equals 10(exp 4) km/sec, while the second component has an equivalent width of approximately 190 eV and appears to be narrower than the first. The total intensity of the Fe K emission decreased by factor of over 3 in response to the decrease in the continuum level, implying that a substantial part of the dominant Fe K emission must originate in a region smaller than that responsible for the soft emission. The variability provides direct evidence that the hard X-ray continuum and Fe K line in this Seyfert 2 are being observed directly through the nuclear obscuring material, not in scattered light.
We present a preliminary analysis of the first high-resolution X-ray spectrum of a Seyfert 2 galaxy, Mkn 3, obtained with the High Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory. The high-energy spectrum (lambda < 4 Ang) is dominated by reflection of the AGN continuum radiation in a cold optically thick medium and contains bright K-alpha fluorescent lines from iron and silicon, as well as weak, blended lines from sulfur and magnesium. The soft X-ray emission (4 < lambda < 23 Ang) is spatially extended along the [O III] ionization cone and shows discrete signatures of emission following recombination and photoexcitation produced in a warm photoionized region. The measured iron L line fluxes indicate that emission from collisionally ionized plasma is almost completely negligible, and does not contribute significantly to the total energy budget of the X-ray emission. We find that significant fractions of the H- and He-like resonance lines, as well as the observed iron L lines are produced through re-emission from the warm absorbing medium observed in Seyfert 1 galaxies. Its X-ray spectral properties are qualitatively consistent with those of a typical Seyfert 1 galaxy viewed at a different orientation, and provide further convincing evidence for the existence of an obscured Seyfert 1 nucleus in Mkn 3. Comment: 16 pages, including 1 table and 2 figures
We discuss the iron and nickel properties in the nuclear X-ray reflecting region of the Circinus Galaxy, studied with XMM-Newton. The main results are: a) from the depth of the Fe Kalpha edge, a value of A_Fe=1.7 in number with respect to the cosmic value (as for Anders & Grevesse 1989) is measured, if the (not directly visible) illuminating spectrum is assumed to be that measured by BeppoSAX. If the slope of the primary power law is left free to vary, a steeper spectrum and a lower iron abundance (about 1.2) are found. b) From the Ni to Fe Kalpha lines flux ratio, a nickel-to-iron abundance ratio of 0.055-0.075 is found. c) The Fe Kbeta/Kalpha flux ratio is slightly lower than expected, possibly due to a mild ionization of iron (which however cannot be much more ionized than X). d) The presence of the Fe Kalpha Compton Shoulder, already discovered by Chandra, is confirmed, its relative flux implying Compton-thick matter. This further supports the identification of the reflecting region with the absorber. Comment: To appear in MNRAS pink pages
We present a XMM–Newton observation of Markarian 304, a Seyfert 1 galaxy at z= 0.066. The EPIC data show that MKN 304 is affected by heavy (NH≈ 1023 cm−2) obscuration arising from ionized gas. A two-phase warm absorber provides an adequate parametrization of this gas. The ionization
parameter of the two components is ξ≈ 6 erg cm−2 s−1 and ξ≈ 90 erg cm−2 s−1, respectively. The observed continuum photon index (Γ≈ 1.9) is typical for Seyfert 1 galaxies. Two significant emission lines
are detected at 0.57 keV and 6.4 keV, respectively. The former is mostly likely due to He-like oxygen triplet emission arising
from an ionized plasma (maybe the warm absorber itself). The latter is due to fluorescent emission of K-shell iron in a low-ionization
state (Fe i–xv). The upper limit for the line width of σKα < 0.18 keV most likely rules out an origin in the inner parts of the accretion disc. Interestingly, the strength of such
line is consistent with the possibility that the emission is produced in the warm absorber itself. However, a substantial
contribution from the torus is plausible too. We have also found a weak (4 per cent of the primary continuum) soft excess
emission component. The presence of this excess could be explained by either emission/scattering from a warm gas or partial
covering, or a combination of them.
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