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 similar to 1.2(-0.3)(+0.3) Chi 10(23) cm(-2)) column. The intrinsic X-ray luminosity (L0.5-30 keV similar to 1.0 Chi 10(43) erg s(-1)) is extremely weak relative to the bolometric luminosity where the 2-10 keV to bolometric luminosity ratio is similar to 0.03% compared to the typical values of 2%-15%. Additionally, Mrk 231 has a low X-ray-to-optical power law slope (alpha(OX) similar to -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.