Issue |
A&A
Volume 483, Number 2, May IV 2008
|
|
---|---|---|
Page(s) | 437 - 452 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:200809590 | |
Published online | 26 March 2008 |
An absorption origin for the X-ray spectral variability of MCG–6-30-15
1
Dept. of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK e-mail: lam@astro.ox.ac.uk
2
Dept. of Physics, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
3
Astrophysics Science Division, NASA/GSFC, Greenbelt, MD 20771, USA
4
Astrophysics Group, School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK
Accepted: 19 March 2008
Context.
The Seyfert I galaxy MCG–6-30-15 shows one of the best examples of
a broad “red wing” of emission in its X-ray spectrum at energies
keV, commonly interpreted as being caused by
relativistically-blurred reflection close to the event horizon of
the black hole.
Aims. We aim to test an alternative model in which absorption
creates the observed spectral shape, explains the puzzling
lack of variability of the red wing and reduces the high reflection albedo,
substantially greater than unity, that is otherwise inferred at energies
keV.
Methods. We compiled all the available long-exposure, high-quality data for MCG–6-30-15:
522 ks of Chandra hetgs,
282 ks of XMM-Newton pn/rgs and
253 ks of Suzaku xis/pin data.
This is the first analysis of this full dataset. We investigated
the spectral variability on timescales >20 ks using principal components
analysis and fitted spectral models to “flux state” and mean spectra
over the energy range keV (depending on detector).
The absorber model was based on the zones previously identified
in the high-resolution grating data. Joint fits were carried out to any
data that were simultaneous.
Results. Multiple absorbing zones covering a wide range of ionisation are required by the grating data, including a highly ionised outflowing zone. A variable partial-covering zone plus absorbed low-ionisation reflection, distant from the source, provides a complete description of the variable X-ray spectrum. A single model fits all the data. We conclude that these zones are responsible for the red wing, its apparent lack of variability, the absorption structure around the Fe Kα line, the soft-band “excess” and the high flux seen in the hard X-ray band. A relativistically-blurred Fe line is not required in this model. We suggest the partial covering zone is a clumpy wind from the accretion disk.
Key words: accretion, accretion disks / galaxies: active / galaxies: individual: MCG–6-30-15 / galaxies: Seyfert
© ESO, 2008
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