NuSTAR Reveals an Intrinsically X-Ray Weak Broad Absorption Line Quasar in the Ultraluminous Infrared Galaxy Markarian 231

Creators: Teng, Stacy H.; Harrison, F. A.; Grefenstette, B. W.; Madsen, K. K.; Walton, D. J.

Abstract

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 (N_H ~ 1.2^(+0.3)_(-0.3) x 10^(23) cm^(–2)) column. The intrinsic X-ray luminosity (L_(0.5 – 30 keV) ~ 1.0 × 10^(43) 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 (α_(OX) ~ –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.

Additional Information

© 2014 American Astronomical Society. Received 2013 August 14; accepted 2014 February 18; published 2014 March 21. We are grateful to the anonymous referee for providing useful comments which improved our manuscript. We thank Wayne Baumgartner, Bret Lehmer, Richard Mushotzky, Jeremy Schnittman, Tahir Yaqoob, and Andreas Zezas for useful discussions. We would also like to thank Lee Armus who provided useful comments in the early planning phase of the NuSTAR ULIRG program. We also thank Roberto Maiolino, David Rupke, and Eckhard Sturm who are co-investigators of the Chandra program. This work was supported under NASA Contract No.NNG08FD60C, and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). The scientific results reported in this article are based in part on observations made by the Chandra X-Ray Observatory and data obtained from the Chandra Data Archive published previously in cited articles. This work, in part, made use of observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). We made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, Caltech, under contract with NASA. S.H.T. is supported by a NASA Postdoctoral Program (NPP) Fellowship. W.N.B. and B.L. acknowledge support by California Institute of Technology (Caltech) NuSTAR subcontract 44A-1092750 and NASA ADP grant NNX10AC99G. F.E.B. acknowledges support from Basal-CATA (PFB-06/2007) and CONICYT-Chile (under grants FONDECYT 1101024 and Anillo ACT1101). A.C. acknowledges support from ASI/INAF grant I/037/12/0-011/13. P.G. acknowledges support from STFC grant reference ST/J003697/1. Facilities: NuSTAR, CXO

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