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Issue A&A
Volume 480, Number 3, March IV 2008
Page(s) 671 - 676
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20078746
Published online 17 January 2008



A&A 480, 671-676 (2008)
DOI: 10.1051/0004-6361:20078746

Heavy absorption and soft X-ray emission lines in the XMM-Newton spectrum of the type 2 radio-loud quasar 3C 234

E. Piconcelli1, S. Bianchi2, G. Miniutti3, F. Fiore1, M. Guainazzi4, E. Jimenez-Bailon5, and G. Matt2

1  Osservatorio Astronomico di Roma (INAF), via Frascati 33, 00040 Monteporzio Catone, Roma, Italy
    e-mail: piconcelli@oa-roma.inaf.it
2  Dipartimento di Fisica, Università degli Studi Roma 3, via della Vasca Navale 84, 00146 Roma, Italy
3  Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
4  European Space Astronomy Center of ESA, Apartado 50727, 28080 Madrid, Spain
5  Instituto de Astronomía, UNAM, Apartado 70264, 04510 Ciudad de México, Mexico

(Received 27 September 2007 / Accepted 20 November 2007)

Abstract
Aims.We report results on a 40 ks XMM-Newton observation of the type 2 quasar 3C 234. Optical spectropolarimetric data have demonstrated the presence of a hidden broad-line region in this powerful (MV $\leq$ -24.2 after reddening and starlight correction) narrow-line FRII radio galaxy. Our analysis is aimed at investigating the X-ray spectral properties of this peculiar source that have remained poorly known so far.
Methods.We analyze the 0.5-10 keV spectroscopic data collected by the EPIC cameras in 2006.
Results.The X-ray spectrum of this radio-loud quasar is typical of a local Compton-thin Seyfert 2 galaxy. It exhibits strong absorption ($N_{\rm H}$ ~ 3.5 $\times$ 1023 cm-2) and a narrow, neutral Fe K$\alpha$ emission line with an equivalent width of $\approx$140 $\pm$ 40 eV.

Our observation also reveals that the soft portion of the spectrum is characterized by strong emission lines with a very low level of scattered primary continuum. A possible explanation of these features in terms of thermal emission from a two-temperature, collisionally ionized plasma emission seems to be unlikely due to the high luminosity estimated for this component (L0.5-2 ~ 6 $\times$ 1042 erg s-1). It is likely that most of the soft X-ray emission originates from a photoionized plasma as commonly observed in obscured, radio-quiet Seyfert-like AGNs.
Conclusions.This X-ray observation has definitively confirmed the presence of a hidden quasar in 3C 234. The line-rich spectrum and the steepness of the hard X-ray continuum ($\Gamma$ $\approx$ 1.7) found in this source weaken the hypothesis that the bulk of the X-ray emission in radio-loud AGNs with high-excitation optical lines arises from jet non-thermal emission.


Key words: galaxies: active -- galaxies: nuclei -- quasars: individual: 3C 234 -- X-rays: galaxies



© ESO 2008


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