1ES 1927+654: Persistent and rapid X-ray variability in an AGN with low intrinsic neutral X-ray absorption and narrow optical emission lines

Free access article

Issue		A&A Volume 397, Number 2, January II 2003


Page(s)		557 - 564
Section		Galactic structure and dynamics
DOI		http://dx.doi.org/10.1051/0004-6361:20021520

A&A 397, 557-564 (2003)
DOI: 10.1051/0004-6361:20021520

1ES 1927+654: Persistent and rapid X-ray variability in an AGN with low intrinsic neutral X-ray absorption and narrow optical emission lines

Th. Boller¹, W. Voges¹, M. Dennefeld², I. Lehmann¹, P. Predehl¹, V. Burwitz¹, E. Perlman^{3, 4}, L. Gallo¹, I. E. Papadakis⁵ and S. Anderson⁶

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
² Institut d'Astrophysique de Paris, 98 bis Bd Arago, 75014 Paris, France
³ Johns Hopkins University, Department of Physics and Astronomy, Baltimore, USA
⁴ University of Maryland, Baltimore County, 1000 Hilltop Circle Baltimore, MD 21250, USA
⁵ University of Crete, IESL, FORTH-hellas, 711 10 Heraklion, Crete, Greece
⁶ University of Washington, Dept. of Astronomy, Box 351580, Seattle, WA 98195, USA

(Received 14 June 2002 / Accepted 15 October 2002 )

Abstract
We present X-ray and optical observations of the X-ray bright AGN 1ES 1927+654. The X-ray observations obtained with ROSAT and Chandra reveal persistent, rapid and large scale variations, as well as steep 0.1-2.4 keV ( $\rm\Gamma = 2.6 \pm 0.3$ ) and 0.3-7.0 keV ( $\rm\Gamma = 2.7 \pm 0.2$ ) spectra. The measured intrinsic neutral X-ray column density is approximately $\rm 7 \times 10^{20}\ cm^{-2}$ . The X-ray timing properties indicate that the strong variations originate from a region, a few hundred light seconds from the central black hole, typical for type 1 AGN.

High quality optical spectroscopy reveals a typical Seyfert 2 spectrum with some host galaxy contamination and no evidence of Fe II multiplets or broad hydrogen Balmer wings. The intrinsic optical extinction derived from the BLR and NLR are $A_V \ge 3.7$ and A_V=1.7, respectively. The X-ray observations give an A_V value of less than 0.58, in contrast to the optical extinction values.

We discuss several ideas to explain this apparent difference in classification including partial covering, an underluminous BLR or a high dust to gas ratio.

Key words: galaxies: active -- galaxies: Seyfert -- galaxies: individual: 1ES 1927+654 -- X-rays: galaxies

Offprint request: Th. Boller, bol@mpe.mpg.de

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