Issue |
A&A
Volume 584, December 2015
|
|
---|---|---|
Article Number | A82 | |
Number of page(s) | 19 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201526790 | |
Published online | 24 November 2015 |
A variable-density absorption event in NGC 3227 mapped with Suzaku and Swift
1
Dr. Remeis-Sternwarte & Erlangen Centre for Astroparticle
Physics, Universität Erlangen-Nürnberg,
Sternwartstrasse 7,
96049
Bamberg,
Germany
e-mail:
tobias.beuchert@sternwarte.uni-erlangen.de
2
Lehrstuhl für Astronomie, Universität Würzburg,
Emil-Fischer-Straße
31, 97074
Würzburg,
Germany
3
Center for Astrophysics and Space Sciences, University of
California, San Diego, 9500 Gilman
Dr., La Jolla,
CA
92093-0424,
USA
4
Centro de Astrobiología (CSIC–INTA), Dep. de Astrofísica, European
Space Astronomy Centre, PO Box 78, Villanueva de la Cañada,
28691
Madrid,
Spain
5 Instituto de Astronomía, Universidad Nacional Autónoma de
México (UNAM), 04510 Ciudad de México, D.F. México
6
European Space Agency, European Space Astronomy Centre, PO Box 78,
Villanueva de la Cañada, 28691
Madrid,
Spain
7
Physics and Astronomy Department, UCLA, Los
Angeles, CA
90095-1562,
USA
8
Harvard-Smithsonian Center for Astrophysics, 60 Garden St.,
Cambridge,
MA
02138,
USA
9 Instituto de Astronomía, Universidad Nacional Autónoma de
México, Km 103, Carret, Tijuana-Ensenada, 22860 Ensenada, BC, Mexico ( PO Box 439027, San
Ysidro, CA, 92143, USA )
10
Instituto de Astrofísica de Andalucía (CSIC),
Apartado 3004,
18080
Granada,
Spain
Received: 19 June 2015
Accepted: 10 August 2015
Context. The morphology of the circumnuclear gas accreting onto supermassive black holes in Seyfert galaxies remains a topic of much debate. As the innermost regions of active galactic nuclei (AGN) are spatially unresolved, X-ray spectroscopy, and in particular line-of-sight absorption variability, is a key diagnostic to map out the distribution of gas.
Aims. Observations of variable X-ray absorption in multiple Seyferts and over a wide range of timescales indicate the presence of clumps/clouds of gas within the circumnuclear material. Eclipse events by clumps transiting the line of sight allow us to explore the properties of the clumps over a wide range of radial distances from the optical/UV broad line region (BLR) to beyond the dust sublimation radius. Time-resolved absorption events have been extremely rare so far, but suggest a range of density profiles across Seyferts. We resolve a weeks-long absorption event in the Seyfert NGC 3227.
Methods. We examine six Suzaku and 12 Swift observations from a 2008 campaign spanning five weeks. We use a model accounting for the complex spectral interplay of three absorbers with different levels of ionization. We perform time-resolved spectroscopy to discern the absorption variability behavior. We also examine the IR to X-ray spectral energy distribution (SED) to test for reddening by dust.
Results. The 2008 absorption event is due to moderately-ionized (log ξ ~ 1.2–1.4) gas covering 90% of the line of sight. We resolve the density profile to be highly irregular, in contrast to a previous symmetric and centrally-peaked event mapped with RXTE in the same object. The UV data do not show significant reddening, suggesting that the cloud is dust-free.
Conclusions. The 2008 campaign has revealed a transit by a filamentary, moderately-ionized cloud of variable density that is likely located in the BLR, and possibly part of a disk wind.
Key words: galaxies: active / galaxies: Seyfert / galaxies: nuclei
© ESO, 2015
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