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Astron. Astrophys. 355, 113-120 (2000)


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A direct view of the AGN powering IRAS12393+3520

M. Guainazzi 1,2, M. Dennefeld  *  3, L. Piro 4, T. Boller 5, P. Rafanelli 6 and M. Yamauchi 7

1 Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
2 XMM SOC, VILSPA, ESA, Apartado 50727, 28080 Madrid, Spain
3 Institut d'Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France
4 Istituto di Astrofisica Spaziale, CNR, Via Fosso del Cavaliere, 00131 Roma, Italy
5 Max-Planck-Institut for Extraterrestrial Physics, 85740 Garching, Germany
6 Università degli Studi di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
7 Astrophysics Laboratory, Department of Applied Physics, Faculty of Engineering, Miyazaki University, 1-1 Gakuen-Kibandai-Nishi, Miyazaki 889-2192, Japan

Received 10 November 1999 / Accepted 21 December 1999

Abstract

We report the first direct X-ray evidence that an AGN is hidden in the center of IRAS12393+3520. An ASCA observation of this target unveiled a bright (0.5-10 keV luminosity [FORMULA] erg s-1) and variable source, with minimum observed doubling/halving time scale comprised in the range 30-75 ks. A model composed by a simple power-law, with photon index [FORMULA]1.8 and an absorption edge, whose threshold energy is consistent with K-shell photoionization of OVII , provides an adequate fit of the spectrum. This suggests that we are observing the emission from the nuclear region through a warm absorber of [FORMULA] a few [FORMULA] cm-2. If it has internal dust with Galactic gas-to-dust ratio, it could explain the lack of broad [FORMULA] emission, even in the episodic presence of a broad [FORMULA] emission line. Optical spectra obtained over several years show indeed variations in the strength of this broad [FORMULA] component. A distribution of dusty, optically thick matter on spatial scales a few hundreds parsec, which does not intercept the line of sight towards the nucleus, is probably required to account simultaneously for the relative [OIII] luminosity deficit in comparison to the X-rays. The high IR to X-ray luminosity ratio is most likely due to intense star formation in the circumnuclear region. IRAS12393+3520 might thus exhibit simultaneously nuclear activity and remarkable star formation.

Key words: X-rays: galaxies – galaxies: active – galaxies: Seyfert – galaxies: individual: IRAS12393+3520 – galaxies: ISM – galaxies: nuclei

* Visiting astronomer, Observatoire de Haute-Provence (OHP), CNRS, France

Send offprint requests to: M. Guainazzi (mguainaz@xmm.vilspa.esa.es)

© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000

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