XMM-Newton spectra of hard spectrum Rosat AGN: X-ray absorption and optical reddening

Free access article

Issue		A&A Volume 420, Number 1, June II 2004


Page(s)		163 - 172
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20035683

A&A 420, 163-172 (2004)
DOI: 10.1051/0004-6361:20035683

XMM-Newton spectra of hard spectrum Rosat AGN: X-ray absorption and optical reddening

F. J. Carrera¹, M. J. Page² and J. P. D. Mittaz³

¹ Instituto de Física de Cantabria (CSIC-UC), Avenida de los Castros, 39005 Santander, Spain
² Mullard Space Science Laboratory-University College London, Surrey RH5 6NT, UK
e-mail: mjp@mssl.ucl.ac.uk
³ University of Huntsville, Alabama, USA
e-mail: mittazj@email.uah.edu

(Received 14 November 2003 / Accepted 3 March 2004)

Abstract
We present the XMM-Newton spectra of three low-redshift intermediate Seyferts (one Sy 1.5, and two Sy 1.8), from our survey of hard spectrum Rosat sources. The three AGN are well fitted by absorbed powerlaws, with intrinsic nuclear photoelectric absorption from column densities between 1.3 and 4.0 $\times$ 10²¹ cm ^-2. In the brightest object the X-ray spectrum is good enough to show that the absorber is not significantly ionized. For all three objects the powerlaw slopes appear to be somewhat flatter ( $\Gamma\sim1.3{-}1.6$ ) than those found in typical unabsorbed Seyferts. The constraints from optical and X-ray emission lines imply that all three objects are Compton-thin. For the two fainter objects, the reddening deduced from the optical broad emission lines in one of them, and the optical continuum in the other, are similar to those expected from the X-ray absorption, if we assume a Galactic gas-to-dust ratio and reddening curve. The broad line region Balmer decrement of our brightest object is larger than expected from its X-ray absorption, which can be explained either by an intrinsic Balmer decrement with standard gas-to-dust ratio, or by a >Galactic gas-to-dust ratio. These $\ge$ Galactic ratios of extinction to photoelectric absorption cannot extend to the high redshift, high luminosity, broad line AGN in our sample, because they have column densities > 10²² cm ^-2, and so their broad line regions would be totally obscured. This means that some effect (e.g., luminosity dependence, or evolution) needs to be present in order to explain the whole population of absorbed AGN.

Key words: galaxies: active -- galaxies: Seyfert -- galaxies: quasars: emission lines -- X-rays: galaxies

Offprint request: F. J. Carrera, carreraf@ifca.unican.es

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