paper

{\it NuSTAR} Reveals an Intrinsically X-ray Weak Broad Absorption Line Quasar in the Ultraluminous Infrared Galaxy Markarian 231

arXiv:1402.4811 · doi:10.1088/0004-637X/785/1/19

Abstract

We present high-energy (3--30 keV) {\it 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 {\it 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 cm) column. The intrinsic X-ray luminosity (L erg s) 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 (). It is a local example of a low-ionization broad absorption line (LoBAL) 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.

15 pages in ApJ style including 6 figures and 1 table. Accepted for publication in ApJ

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