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Weak Hard X-Ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-Ray Weakness

Luo, B. and Brandt, W. N. and Alexander, D. M. and Stern, D. and Teng, S. H. and Arévalo, P. and Bauer, F. E. and Boggs, S. E. and Christensen, F. E. and Comastri, A. and Craig, W. W. and Farrah, D. and Gandhi, P. and Hailey, C. J. and Harrison, F. A. and Koss, M. and Ogle, P. and Puccetti, S. and Saez, C. and Scott, A. E. and Walton, D. J. and Zhang, W. W. (2014) Weak Hard X-Ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-Ray Weakness. Astrophysical Journal, 794 (1). Art. No. 70. ISSN 0004-637X. doi:10.1088/0004-637X/794/1/70.

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We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z = 0.148–1.223, are among the optically brightest and most luminous BAL quasars known at z < 1.3. However, their rest-frame ≈2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with ≲45 counts in the 3–24 keV band, and the other three are not detected. The hard X-ray (8–24 keV) weakness observed by NuSTAR requires Compton-thick absorption if these objects have nominal underlying X-ray emission. However, a soft stacked effective photon index (Γ_eff ≈ 1.8) for this sample disfavors Compton-thick absorption in general. The uniform hard X-ray weakness observed by NuSTAR for this and the pilot samples selected with <10 keV weakness also suggests that the X-ray weakness is intrinsic in at least some of the targets. We conclude that the NuSTAR observations have likely discovered a significant population (≳33%) of intrinsically X-ray weak objects among the BAL quasars with significantly weak <10 keV emission. We suggest that intrinsically X-ray weak quasars might be preferentially observed as BAL quasars.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Luo, B.0000-0002-9036-0063
Brandt, W. N.0000-0002-0167-2453
Alexander, D. M.0000-0002-5896-6313
Stern, D.0000-0003-2686-9241
Bauer, F. E.0000-0002-8686-8737
Boggs, S. E.0000-0001-9567-4224
Christensen, F. E.0000-0001-5679-1946
Comastri, A.0000-0003-3451-9970
Farrah, D.0000-0003-1748-2010
Gandhi, P.0000-0003-3105-2615
Harrison, F. A.0000-0003-2992-8024
Koss, M.0000-0002-7998-9581
Ogle, P.0000-0002-3471-981X
Puccetti, S.0000-0002-2734-7835
Walton, D. J.0000-0001-5819-3552
Zhang, W. W.0000-0002-1426-9698
Additional Information:© 2014. The American Astronomical Society. Received 21 May 2014, accepted for publication 14 August 2014. Published 24 September 2014. We acknowledge support from the California Institute of Technology (Caltech) NuSTAR subcontract 44A-1092750 (B.L., W.N.B.), NASA ADP grant NNX10AC99G (B.L., W.N.B.), NASA Postdoctoral Program (S.H.T.), CONICYT-Chile FONDECYT 1140304 (P.A.) and 1141218 (F.E.B.), "EMBIGGEN" Anillo ACT1101 (P.A., F.E.B.), Basal-CATA PFB-06/2007 (F.E.B.), Project IC120009 "Millennium Institute of Astrophysics (MAS)" of Iniciativa Científica Milenio del Ministerio de Economía, Fomento y Turismo (F.E.B.), ASI/INAF grant I/037/12/0-011/13 (A.C.), STFC grant ST/J003697/1 (P.G.), and the Swiss National Science Foundation (NSF) grant PP00P2 138979/1 (M.K.). We thank K. Forster for help with the observation planning, and we thank T. Yaqoob for helpful discussions. We thank the referee 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 NuSTARDAS 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
NASA Postdoctoral ProgramUNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1140304
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1141218
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
Agenzia Spaziale Italiana (ASI)I/037/12/0-011/13
Science and Technology Facilities Council (STFC)ST/J003697/1
Swiss National Science Foundation (SNSF)PP00P2 138979
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords:accretion, accretion disks; galaxies: active; galaxies: nuclei; quasars: absorption lines; quasars: emission lines; X-rays: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20141106-132623873
Persistent URL:
Official Citation:Weak Hard X-Ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-Ray Weakness B. Luo et al. 2014 ApJ 794 70
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51379
Deposited On:06 Nov 2014 23:08
Last Modified:10 Nov 2021 19:10

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