Teng, Stacy H.16; Brandt, W. N.17; Harrison, F. A.18; Luo, B.17; Alexander, D. M.6; Bauer, F. E.7; Boggs, S. E.19; Christensen, Finn Erland1; Comastri, A.9; Craig, W. W.19; Fabian, A. C.10; Farrah, D.11; Fiore, F.12; Gandhi, P.6; Grefenstette, B. W.18; Hailey, C. J.20; Hickox, R. C.21; Madsen, K. K.18; Ptak, A. F.16; Rigby, J. R.16; Risaliti, G.9; Saez, C.7; Stern, D.18; Veilleux, S.22; Walton, D. J.18; Wik, D. R.16; Zhang, W. W.16
1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 NASA Goddard Space Flight Center4 Pennsylvania State University5 California Institute of Technology6 Durham University7 Pontifícia Universidade Católica8 University of California at Berkeley9 National Institute for Astrophysics10 Institute of Astronomy11 Virginia Tech12 Osservatorio Astronomico di Roma13 Columbia University14 Dartmouth College15 University of Maryland16 NASA Goddard Space Flight Center17 Pennsylvania State University18 California Institute of Technology19 University of California at Berkeley20 Columbia University21 Dartmouth College22 University of Maryland
We present high-energy (3-30 keV) NuSTAR observations of the nearest quasar, the ultraluminous infrared galaxy (ULIRG) Markarian 231 (Mrk 231), supplemented with new and simultaneous low-energy (0.5-8 keV) data from Chandra. The source was detected, though at much fainter levels than previously reported, likely due to contamination in the large apertures of previous non-focusing hard X-ray telescopes. The full band (0.5-30 keV) X-ray spectrum suggests the active galactic nucleus (AGN) in Mrk 231 is absorbed by a patchy and Compton-thin ( cm-2) column. The intrinsic X-ray luminosity (L0.5 - 30 keV ~ 1.0 × 1043 erg s-1) is extremely weak relative to the bolometric luminosity where the 2-10 keV to bolometric luminosity ratio is ~0.03% compared to the typical values of 2%-15%. Additionally, Mrk 231 has a low X-ray-to-optical power law slope (αOX ~ -1.7). It is a local example of a low-ionization broad absorption line quasar that is intrinsically X-ray weak. The weak ionizing continuum may explain the lack of mid-infrared [O IV], [Ne V], and [Ne VI] fine-structure emission lines which are present in sources with otherwise similar AGN properties. We argue that the intrinsic X-ray weakness may be a result of the super-Eddington accretion occurring in the nucleus of this ULIRG, and may also be naturally related to the powerful wind event seen in Mrk 231, a merger remnant escaping from its dusty cocoon.