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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Teng, S.H., Brandt, W.N., Harrison, F.A., Luo, B., Alexander, D.M., Bauer, F.E., Boggs, S.E., Christensen, F.E., Comastri, A., Craig, W.W., Fabian, A.C., Farrah, D., Fiore, F., Gandhi, P., Grefenstette, B.W., Hailey, C.J., Hickox, R.C., Madsen, K.K., Ptak, A., Rigby, J.R., Risaliti, G., Saez, C., Stern, D., Veilleux, S., Walton, D.J., Wik, D.R. & Zhang, W.W. (2014). NuSTAR Reveals an Intrinsically X-ray Weak Broad Absorption Line Quasar in the Ultraluminous Infrared Galaxy Markarian 231. The Astrophysical Journal 785(1): 19.

Author(s) from Durham


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 ($N_{\rm H} \sim 1.2^{+0.3}_{-0.3}\times 10^{23}$ cm–2) column. The intrinsic X-ray luminosity (L 0.5 – 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.