We have conducted an extensive X-ray spectral variability study of a sample of 20 Compton-thin type II galaxies using broadband spectra from XMM-Newton, Chandra, and Suzaku. The aim is to study the ...variability of the neutral intrinsic X-ray obscuration along the line of sight and investigate the properties and location of the dominant component of the X-ray-obscuring gas. The observations are sensitive to absorption columns of ∼ 1020.5-24 cm−2 of fully and partially covering neutral and/or lowly ionized gas on timescales spanning days to well over a decade. We detected variability in the column density of the full-covering absorber in 7/20 sources, on timescales of months to years, indicating a component of compact-scale X-ray-obscuring gas lying along the line of sight of each of these objects. Our results imply that torus models incorporating clouds or over-dense regions should account for line-of-sight column densities as low as ∼a few ×1021 cm−2. However, 13/20 sources yielded no detection of significant variability in the full-covering obscurer, with upper limits of ΔNH spanning 1021-23 cm−2. The dominant absorbing media in these systems could be distant, such as kiloparsec-scale dusty structures associated with the host galaxy, or a homogeneous medium along the line of sight. Thus, we find that overall, strong variability in full-covering obscurers is not highly prevalent in Compton-thin type IIs, at least for our sample, in contrast to previous results in the literature. Finally, 11/20 sources required a partial-covering, obscuring component in all or some of their observations, consistent with clumpy near-Compton-thick compact-scale gas.
ABSTRACT
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.
We have carried out an extensive X-ray spectral analysis of a sample of galaxies exhibiting molecular outflows (MOX sample) to characterize the X-ray properties and investigate the effect of active ...galactic nuclei (AGNs) on the dynamical properties of the molecular outflows (MOs). We find that the X-ray bolometric correction (L2-10 keV/LAGN) of these sources ranges from ∼10−4.5 to 10−0.5, with ∼70% of the sources below 10−2, implying a weak X-ray emission relative to the AGN bolometric luminosity (LAGN). However, the upper limit on the 2-10 keV luminosity ( ) obtained from 12 m flux, following the correlation derived by Asmus et al., is ∼0.5-3 orders of magnitude larger than the L2-10 keV values estimated using X-ray spectroscopy, implying a possibility that the MOX sources host normal AGNs (not X-ray weak), and their X-ray spectra are extremely obscured. We find that both L2-10 keV and LAGN correlate strongly with the MO velocity and the mass outflow rates ( ), implying that the central AGN plays an important role in driving these massive outflows. However, we also find statistically significant positive correlations between the starburst emission and MO mass outflow rate, versus , and L0.6-2keV versus , which implies that starbursts can generate and drive the MOs. The correlations of MO velocity and with AGN luminosities are found to be stronger compared to those with the starburst luminosities. We conclude that both starbursts and AGNs play a crucial role in driving the large-scale MO.
The accreting black hole binary XTE J1752-223 was observed in a stable hard state for 25 days by the Rossi X-ray Timing Explorer (RXTE), yielding a 3-140 keV spectrum of unprecedented statistical ...quality. Its published model required a single-Comptonization spectrum reflecting from a disk close to the innermost stable circular orbit. We studied that model as well as a number of other single-Comptonization models (yielding similarly low inner radii), but found they violate a number of basic physical constraints, e.g., their compactness is much above the maximum allowed by pair equilibrium. We also studied the contemporaneous 0.55-6 keV spectrum from the Swift/X-ray Telescope and found it well fitted by an absorbed power law and a disk blackbody with the innermost temperature of 0.1 keV. The normalization of the disk blackbody corresponds to an inner radius of 20 gravitational radii and its temperature, to irradiation of the truncated disk by a hot inner flow. We have also developed a Comptonization/reflection model including the disk irradiation and intrinsic dissipation, but found that it does not yield any satisfactory fits. On the other hand, we found that the ≤10 keV band from RXTE is much better fitted by a reflection from a disk with the inner radius 100 gravitational radii, which model then underpredicts the spectrum at >10 keV by <10%. We argue that the most plausible explanation of the above results is inhomogeneity of the source, with the local spectra hardening with the decreasing radius. Our results support the presence of a complex Comptonization region and a large disk truncation radius in this source.
We have analyzed spectra for all active galactic nuclei (AGNs) in the Rossi X-ray Timing Explorer archive. We present long-term average values of absorption, Fe line equivalent width (EW), Compton ...reflection, and photon index, and calculate 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 1s and 2s 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 report on deep (40ks
$\times$
4) observations of the bright broad line radio galaxy 3C 120 using Suzaku. The observations were spaced one week apart, and sampled a range of continuum fluxes. An ...excellent broadband spectrum was obtained over two decades of frequency (0.6 to 50 keV) within each 40ks exposure. We clearly resolved the iron K emission-line complex, finding that it consists of a narrow K
$\alpha$
core (
$\sigma \simeq$
110 eV or an EW of 60 eV), a 6.9 keV line, and an underlying broad iron line. Our confirmation of the broad line contrasts with the XMM-Newton observation in 2003, where the broad line was not required. The most natural interpretation of the broad line is iron K line emission from a face-on accretion disk that is truncated at ~ 10
r
g
. Above 10 keV, a relatively weak Compton hump was detected (reflection fraction of
R
$\simeq$
0.6), superposed on the primary X-ray continuum of
$\Gamma \simeq$
1.75. Thanks to the good photon statistics and low background of the Suzaku data, we clearly confirm the spectral evolution of 3C 120, whereby the variability amplitude decreases with increasing energy. More strikingly, we discovered that the variability is caused by a steep power-law component of
$\Gamma \simeq$
2.7, possibly related to non-thermal jet emission. We discuss our findings in the context of similarities and differences between radio-loud/quiet objects.
We present detailed time-averaged X-ray spectroscopy in the 0.5–10 keV band of the Seyfert 1.9 galaxy NGC 2992 with the Suzaku X-ray Imaging Spectrometer (XIS). There is an Fe K line emission complex ...that we model with broad and narrow lines and we show that the intensities of the two components are decoupled at a confidence level
$ \gt3\sigma$
. The broad line (
$\mathrm{EW} = 118^{+32}_{-61} \,\mathrm{eV}$
) could originate in an accretion disk (inclined at
$ \gt30^{\circ}$
). The narrow Fe
$\mathrm{K}\alpha$
line (
$\mathrm{EW} =163^{+47}_{-26} \,\mathrm{eV}$
) is unresolved by the XIS at 99% confidence and likely originates in distant matter. A significant (narrow) Fe
$\mathrm{K}\beta$
line is also detected and we describe a new robust method to constrain the ionization state of Fe in the distant line emitter (e.g. the putative obscuring torus). The method does not require any knowledge of possible gravitational and Doppler energy shifts and we deduce that the predominant ionization state of Fe in the distant matter is lower than Fe VIII (at 99% confidence), conservatively taking into account residual calibration uncertainties and theoretical and experimental uncertainties in the Fe K fluorescent line energies. We argue that the narrow Fe
$\mathrm{K}\alpha$
and Fe
$\mathrm{K}\beta$
lines likely originate in a Compton-thin structure.
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