A Chandra observation of the ultraluminous infrared galaxy IRAS 19254-7245 (The Superantennae): X-ray emission from the Compton-thick active galactic nucleus and the diffuse starburst

Abstract

We present a Chandra observation of IRAS 19254-7245, a nearby ultraluminous infrared galaxy also known as the Superantennae. The high spatial resolution of Chandra allows us to disentangle for the first time the diffuse starburst (SB) emission from the embedded Compton-thick active galactic nucleus (AGN) in the southern nucleus. No AGN activity is detected in the northern nucleus. The 2-10keV spectrum of the AGN emission is fitted by a flat power law (Γ = 1.3) and an He-like Fe Kα line with equivalent width 1.5keV, consistent with previous observations. The Fe Kα line profile could be resolved as a blend of a neutral 6.4keV line and an ionized 6.7keV (He-like) or 6.9keV (H-like) line. Variability of the neutral line is detected compared with the previous XMM-Newton and Suzaku observations, demonstrating the compact size of the iron line emission. The spectrum of the galaxy-scale extended emission excluding the AGN and other bright point sources is fitted with a thermal component with a best-fit kT of 0.8 keV. The 2-10keV luminosity of the extended emission is about one order of magnitude lower than that of the AGN. The basic physical and structural properties of the extended emission are fully consistent with a galactic wind being driven by the SB. A candidate ultraluminous X-ray source is detected 8″ south of the southern nucleus. The 0.3-10keV luminosity of this off-nuclear point source is 6 × 10 40ergs-1 if the emission is isotropic and the source is associated with the Superantennae. © 2012. The American Astronomical Society. All rights reserved..