Please use this identifier to cite or link to this item: http://hdl.handle.net/2307/362
Title: Unabsorbed Seyfert 2 galaxies: the case of 'naked' AGN
Authors: Panessa, F.
Carrera, F. J.
Bianchi, Stefano
Corral, A.
Gastaldello, F.
Barcons, X.
Bassani, L.
Matt, Giorgio
Monaco, L.
Keywords: ACTIVE GALACTIC NUCLEI
X-RAY-CLUSTERS
ABSORBING COLUMN DENSITIES
H-ALPHA-EMISSION
XMM-NEWTON
SURFACE BRIGHTNESS
ENERGY-DISTRIBUTIONS
COMPTON-THICK
OUTER REGIONS
UNIFIED MODEL
Issue Date: 10-Aug-2009
Publisher: Wiley-Blackwell
Abstract: Hawkins reported on a class of 'naked' active galactic nuclei (AGN)characterized by strong amplitude optical brightness variability and the complete absence of broad emission lines in the optical spectrum. The variability suggests that the nucleus is seen directly, however the absence of broad lines contradicts the simple formulation of Unified Models for AGN. We present the results of quasi-simultaneous spectroscopic observations with XMM-Newton and New Technology Telescope(NTT) (La Silla) of two 'naked' AGN. We confirm the 'naked' nature of Q2131-427 for which no broad emission line components have been detected in the optical spectrum and its X-ray spectrum shows no signs of intrinsic absorption. The optical and X-ray mismatch in this source cannot be ascribed to a high nuclear dust-to-gas ratio and a Compton-thick nature is ruled out on the basis of the high F-X/F-[OIII] ratio. The broad-line region (BLR) may be completely absent in this source, possibly as a consequence of its low Eddington ratio. On the other hand, the optical spectrum of Q2130-431 shows H alpha and H beta broad emission line components, revealing the presence of a BLR. A mild X-ray absorption is expected in intermediate type 1.8 Seyfert galaxies like Q2130-431, however we put a very low upper limit on the column density (<2 x 10(20) cm(-2)), also the low Balmer decrement suggests that the BLR itself does not suffer from reddening. We propose that in this object the BLR is intrinsically weak, making a case of 'true' intermediate Seyfert galaxy. We also report on the X-ray detection of the Abell 3783 galaxy cluster in the XMM-Newton field of view of the Q2131-427 observation.
URI: http://hdl.handle.net/2307/362
ISSN: 0035-8711
DOI: 10.1111/j.1365-2966.2009.15225.x
Appears in Collections:A - Articolo su rivista
X_Dipartimento di Fisica 'Edoardo Amaldi'

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