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Weak Hard X-Ray Emission from Two Broad Absorption Line Quasars Observed with NuSTAR: Compton-thick Absorption or Intrinsic X-Ray Weakness?

Luo, B. and Harrison, F. A. and Fuerst, F. and Grefenstette, B. W. and Madsen, K. K. and Walton, D. J. and Ogle, P. (2013) Weak Hard X-Ray Emission from Two Broad Absorption Line Quasars Observed with NuSTAR: Compton-thick Absorption or Intrinsic X-Ray Weakness? Astrophysical Journal, 772 (2). Art. No. 153. ISSN 0004-637X. doi:10.1088/0004-637X/772/2/153.

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We 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 ≈400-600 hard X-ray (≳ 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed (N_H ≾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 ≈ 7 × 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 Kα 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%.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Luo, B.0000-0002-9036-0063
Harrison, F. A.0000-0003-2992-8024
Fuerst, F.0000-0003-0388-0560
Grefenstette, B. W.0000-0002-1984-2932
Madsen, K. K.0000-0003-1252-4891
Walton, D. J.0000-0001-5819-3552
Ogle, P.0000-0002-3471-981X
Additional Information:© 2013 The American Astronomical Society. Received 2013 April 3; accepted 2013 June 14; published 2013 July 17. We acknowledge support from the California Institute of Technology (Caltech) NuSTAR subcontract 44A-1092750 (B.L. and W.N.B.), NASA ADP Grant NNX10AC99G (B.L. and W.N.B.), the Leverhulme trust and the Science Technology and Facilities Council (D.M.A.), Basal-CATA Grant PFB-06/2007 and CONICYT-Chile Grants FONDECYT 1101024 and Anillo ACT1101 (F.E.B.), and CONICYT-Chile Grant FONDECYT 3120198 (C.S.). We thank M. Young for help with the planning of this project and K. Forster for help with the NuSTAR data access, and we thank M. Balokovic, K. Boydstun, T. N. Lu, B. P. Miller, Jianfeng Wu, and T. Yaqoob for helpful discussions. We thank the referee, S. C. Gallagher, for carefully reviewing the manuscript and providing helpful comments. This work was supported under NASA contract No. NNG08FD60C, and made use of data from the NuSTAR mission, a project led by Caltech, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of NuSTAR-DAS jointly developed by the ASI Science Data Center (ASDC, Italy) and Caltech (USA).
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Caltech NuSTAR subcontract44A-1092750
Leverhulme TrustUNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1101024
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)Anillo ACT1101
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)3120198
Subject Keywords:accretion, accretion disks – galaxies: active – galaxies: nuclei – quasars: absorption lines – quasars: emission lines – X-rays: general
Issue or Number:2
Record Number:CaltechAUTHORS:20130828-093434856
Persistent URL:
Official Citation:Weak Hard X-Ray Emission from Two Broad Absorption Line Quasars Observed with NuSTAR: Compton-thick Absorption or Intrinsic X-Ray Weakness? B. Luo et al. 2013 ApJ 772 153
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40969
Deposited By: Tony Diaz
Deposited On:30 Aug 2013 18:11
Last Modified:10 Nov 2021 04:24

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