587 research outputs found
Dust lanes, thick absorbers, and the unification model for Seyfert galaxies
A modification of the popular unification model for Seyfert galaxies is
proposed, which takes into account recent observational findings on the
statistical properties of both type 1 and type 2 Seyferts. In the proposed
scenario, Compton-thick Seyfert 2 galaxies are those sources observed through
compact, thick matter (the `torus'), while Compton-thin/intermediate Seyfert
galaxies are obscured by dust lanes at larger distances.Comment: 4 pages, 1 figure. Accepted for publication in A&A Letter
A receding torus model for the Iwasawa-Taniguchi effect for Compton-thick AGN
Recently, Boorman et al. (2018) reported on the discovery of the
Iwasawa-Taniguchi (I-T) effect (a.k.a. X-ray Baldwin effect) for Compton-thick
AGN. They measured a decrease of the 6.4 keV iron line equivalent width with
the 12mu luminosity, assumed as a proxy for the intrinsic X-ray luminosity,
which in Compton-thick AGN is not directly observable. One of the most popular
explanations of the classic I-T effect is the so-called receding torus model,
i.e. the decrease of the covering factor of the molecular `torus' with X-ray
luminosity. In this paper we show that an I-T effect for Compton-thick AGN is
indeed expected in the receding torus model, assuming that the torus is
funnelling the primary X-ray luminosity which is then scattered in a `hot
mirror'. We found that the observed relation is well reproduced provided that
the typical column density of the `hot mirror' is about 7.5x10^{22} cm^{-2}.Comment: 4 pages, 2 figures. Accepted for publication in MNRA
The properties of the absorbing and line emitting material in IGR J16318-4848
We have performed a detailed analysis of the XMM-Newton observation of IGR
J16318-4848, to study the properties of the matter responsible for the
obscuration and for the emission of Fe and Ni lines. Even if the line of sight
material has a column density of about 2x10^24 cm^-2, from the Fe Kalpha line
EW and Compton Shoulder we argue that the matter should have an average column
density of a few x10^23 cm^-2, along with a covering factor of about 0.1-0.2.
The iron Kalpha line varies on time scales as short as 1000 s, implying a size
of the emitting region smaller than about 3x10^13 cm. The flux of the line
roughly follows the variations of the continuum, but not exactly, suggesting a
variation of the geometrical properties of the emitting region on similar time
scales.Comment: accepted for publication in MNRAS, pink page
The iron Kalpha Compton Shoulder in transmitted and reflected spectra
We calculate the Equivalent Widht of the Core and the centroid energy and
relative flux of the 1st order Compton Shoulder of the iron Kalpha 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 XMM-Newton and Chandra
satellites, and the present work aims to provide a tool to derive informations
on the geometry and element abundances of the line emitting matter from Compton
Shoulder measurements.Comment: 4 pages; accepted for publication in MNRA
The Contribution of the Obscuring Torus to the X--Ray Spectrum of Seyfert Galaxies: A Test for the Unification Model
The presence of an obscuring torus around the nucleus of Seyfert galaxies, as
supposed in the popular unification scheme, can strongly modify the X--ray
spectrum for both type 1 and 2 Seyfert galaxies. We find that if the torus is
Compton thick, it can scatter at small angles a significant fraction of the
nuclear radiation, and contribute to the continuum of Seyfert 1 galaxies above
10 keV, and to the fluorescence iron line at 6.4 keV. At large
inclination angles and for large torus column densities, the spectrum is
attenuated by photoabsorption and Compton scattering, while the iron
fluorescence line produced by the torus can have large equivalent widths. Even
after dilution by the continuum scattered by the warm material outside the
torus, this iron line could be strong enough to explain the ``cold" component
in the spectrum of NGC 1068. We stress that the complex pattern of the
predicted variability can be a powerful tool for constraining the parameters of
the model, such as the column density of the torus, its inclination and the
amount of warm scattering material.Comment: 19 pages, Plain Tex, SISSA ref. 175/93/
X-ray spectra transmitted through Compton-thick absorbers
X-ray spectra transmitted through matter which is optically thick to Compton
scattering are computed by means of Monte Carlo simulations. Applications to
the BeppoSAX data of the Seyfert 2 galaxy in Circinus, and to the spectral
modeling of the Cosmic X-ray Background, are discussed.Comment: 10 pages. Accepted for publication in New Astronom
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