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

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 \simm 1.4 keV) Fe emission line at 6.49+/- 0.1 keV (rest-frame). The X-ray spectrum requires a soft thermal component (kT\simm0.9 keV; L_0.5-2\simm 4*E⁴¹ erg s^-1), likely associated with the starburst, and a hard power-law continuum above 2 keV (observed L_2-10\simm 4*E⁴² 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.