Weak hard X-ray emission from two broad absorption line quasars observed with NuSTAR: Compton-thick absorption or intrinsic X-ray weakness?

Virginia TechLuo, B.Brandt, W. N.Alexander, D. M.Harrison, F. A.Stern, D.Bauer, F. E.Boggs, S. E.Christensen, F. E.Comastri, A.Craig, W. W.Fabian, A. C.Farrah, D.Fiore, F.Fuerst, F.Grefenstette, B. W.Hailey, C. J.Hickox, R.Madsen, K. K.Matt, G.Ogle, P.Risaliti, G.Saez, C.Teng, S. H.Walton, D. J.Zhang, W. W.2014-02-252014-02-252013-08B. Luo et al. 2013. "Weak hard X-ray emission from two broad absorption line quasars observed with NuSTAR: Compton-thick absorption or intrinsic X-ray weakness?," ApJ 772 153 doi:10.1088/0004-637X/772/2/1530004-637Xhttp://hdl.handle.net/10919/25553We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain approximate to 400-600 hard X-ray (greater than or similar to 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed (N-H less than or similar to 10(24) cm(-2)). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N-H approximate to 7 x 10(24) cm(-2) if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe K alpha line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.en-USIn Copyrightaccretion, accretion disksgalaxies: activegalaxies: nucleiquasars:absorption linesquasars: emission linesx-rays: generalactive galactic nucleidigital sky surveyspectralenergy-distributionsoptically selected quasarsxmm-newtonspectroscopyhubble-space-telescopeaccretion disk windsradio-loudquasarsseyfert 1 galaxies7th data releaseWeak hard X-ray emission from two broad absorption line quasars observed with NuSTAR: Compton-thick absorption or intrinsic X-ray weakness?Article - Refereedhttp://m.iopscience.iop.org/0004-637X/772/2/153/pdf/0004-637X_772_2_153.pdfAstrophysical Journalhttps://doi.org/10.1088/0004-637x/772/2/153