XMM-Newton observations of ULIRGs: A Compton-thick AGN in IRAS 19254–7245

¹ INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
² Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
³ INAF - Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
⁴ IASF - CNR, Sezione di Bologna, via Gobetti 101, 40129 Bologna, Italy
⁵ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ INAF - Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy
⁷ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138, USA

Corresponding author: V. Braito, braito@pd.astro.it

Received: 6 August 2002
Accepted: 7 November 2002

Abstract

We present the XMM-Newton observation of the merging system IRAS 19254-7245, also known as The Superantennae, whose southern nucleus is classified as a Seyfert 2 galaxy. The XMM- Newton data have allowed us to perform a detailed X-ray imaging and spectral analysis of this system. We clearly detect, for the first time in this system, a strong ( keV) Fe emission line at keV (rest-frame). The X-ray spectrum requires a soft thermal component ( keV;  erg s^-1), likely associated with the starburst, and a hard power-law continuum above 2 keV (observed  erg s^-1 ). We confirm the flatness of this latter component, already noted in previous ASCA data. This flatness, together with the detection of the strong Fe-Kα line and other broad band indicators, suggest the presence of a Compton-thick AGN with intrinsic luminosity ≳10⁴⁴ erg s^-1. We show that a Compton-thick model can perfectly reproduce the X-ray spectral properties of this object.