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Issue A&A
Volume 398, Number 1, January IV 2003
Page(s) 107 - 111
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20021633



A&A 398, 107-111 (2003)
DOI: 10.1051/0004-6361:20021633

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

V. Braito1, 2, A. Franceschini2, R. Della Ceca3, P. Severgnini3, L. Bassani4, M. Cappi4, G. Malaguti4, G. G. C. Palumbo5, M. Persic6, G. Risaliti7, 8 and M. Salvati7

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

(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 ( $EW \sim 1.4$ keV) Fe emission line at $6.49\pm 0.1$ keV (rest-frame). The X-ray spectrum requires a soft thermal component ( $kT\sim0.9$ keV; $L_{0.5-2}\sim 4\times10^{41}$  erg s -1), likely associated with the starburst, and a hard power-law continuum above 2 keV (observed $L_{2-10}\sim 4\times10^{42}$ 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-K ${\alpha}$ line and other broad band indicators, suggest the presence of a Compton-thick AGN with intrinsic luminosity $\gtrsim$10 44 erg s -1. We show that a Compton-thick model can perfectly reproduce the X-ray spectral properties of this object.


Key words: galaxies: active -- galaxies: starburst -- X-rays: galaxies -- galaxies: individual: IRAS 19254-7245

Offprint request: V. Braito, braito@pd.astro.it

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