2017ApJ...841...44P

We present an imaging and spectral analysis of the nuclear region of the ultraluminous infrared galaxy merger of Arp 220, using deep Chandra-ACIS observations summing up to ∼300 ks. Narrowband imaging with subpixel resolution of the innermost nuclear region reveals two distinct Fe-K emitting sources, coincident with the infrared and radio nuclear clusters. These sources are separated by 1' (∼380 pc). The X-ray emission is extended and elongated in the eastern (E) nucleus, like the disk emission observed in millimeter radio images, suggesting a starburst dominance in this region. We estimate an Fe-K equivalent width of 1 keV for both sources and observe 2-10 keV luminosities of ∼2×10⁴⁰ erg s^–1 (western, W) and ∼3×10⁴⁰ erg s^–1 (E). In the 6-7 keV band the emission from these regions is dominated by the 6.7 keV Fe XXV line, suggesting a contribution from collisionally ionized gas. The thermal energy content of this gas is consistent with the kinetic energy injection in the interstellar medium by SNe II. However, nuclear winds from a hidden active galactic nucleus (AGN) (υ∼2000 km s^–1) cannot be excluded. The 3σ upper limits on the neutral Fe-Kα flux of the nuclear regions correspond to the intrinsic AGN 2-10 keV luminosities of 1×10⁴² erg s^–1 (W) and 0.4×10⁴² erg s^–1 (E). For typical AGN spectral energy distributions the bolometric luminosities are 3×10⁴³ erg s^–1 (W) and 8×10⁴³ erg s^–1 (E), and black hole masses of 1×10⁵ M_☉ (W) and 5×10⁵ M_☉ (E) are evaluated for Eddington limited AGNs with a standard 10% efficiency.