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 } \sim 1.2 ^ { +0.3 } _ { -0.3 } \times 10 ^ { 23 } cm ^ { -2 } ) column .
The intrinsic X-ray luminosity ( L _ { 0.5 - 30 ~ { } keV } \sim 1.0 \times 10 ^ { 43 } erg s ^ { -1 } ) is extremely weak relative to the bolometric luminosity where the 2–10 keV to bolometric luminosity ratio is \sim 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 } \sim - 1.7 ) .
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 .