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NuSTAR Observations of Heavily Obscured Quasars at z ~ 0.5

Lansbury, G. B. and Baloković, M. and Grefenstette, B. W. and Harrison, F. A. (2014) NuSTAR Observations of Heavily Obscured Quasars at z ~ 0.5. Astrophysical Journal, 785 (1). Art. No. 17. ISSN 0004-637X.

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We present NuSTAR hard X-ray observations of three Type 2 quasars at z ≈ 0.4-0.5, optically selected from the Sloan Digital Sky Survey. Although the quasars show evidence for being heavily obscured, Compton-thick systems on the basis of the 2-10 keV to [O III] luminosity ratio and multiwavelength diagnostics, their X-ray absorbing column densities (N_H) are poorly known. In this analysis, (1) we study X-ray emission at >10 keV, where X-rays from the central black hole are relatively unabsorbed, in order to better constrain N_H. (2) We further characterize the physical properties of the sources through broad-band near-UV to mid-IR spectral energy distribution analyses. One of the quasars is detected with NuSTAR at >8 keV with a no-source probability of <0.1%, and its X-ray band ratio suggests near Compton-thick absorption with N_H≳5 × 10^(23) cm^(–2). The other two quasars are undetected, and have low X-ray to mid-IR luminosity ratios in both the low-energy (2-10 keV) and high-energy (10-40 keV) X-ray regimes that are consistent with extreme, Compton-thick absorption (N_H≳10^(24) cm^(–2)). We find that for quasars at z ~ 0.5, NuSTAR provides a significant improvement compared to lower energy (<10 keV) Chandra and XMM-Newton observations alone, as higher column densities can now be directly constrained.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lansbury, G. B.0000-0002-5328-9827
Harrison, F. A.0000-0003-2992-8024
Additional Information:© 2014 American Astronomical Society. Received 2013 November 12; accepted 2014 February 10; published 2014 March 21. We acknowledge financial support from the Science and Technology Facilities Council (STFC) grants ST/K501979/1 (G.B.L.), ST/I001573/1 (D.M.A. and A.D.M.) and ST/J003697/1 (P.G.), the Leverhulme Trust (D.M.A. and J.R.M.), Gemini-CONICYT grant 32120009 (R.J.A.), NSF AST award 1008067 (D.R.B.), the International Fulbright Science and Technology Award (M.B.), Basal-CATA PFB-06/2007 (F.E.B.), CONICYT-Chile grant FONDECYT 1101024 (F.E.B.), CONICYT-Chile grant Anillo ACT1101 (F.E.B.), Caltech NuSTAR subcontract 44A-1092750 (W.N.B. and B.L.), NASA ADP grant NNX10AC99G (W.N.B. and B.L.), NASA ADAP award NNX12AE38G (R.C.H.), National Science Foundation grant 1211096 (R.C.H.), and Swiss National Science Foundation grant PP00P2_138979/1 (M.K.). We thank the referee for the constructive comments, which helped improve our study. This work was supported under NASA contract No. NNG08FD60C, and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, 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 the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC) ST/K501979/1
Science and Technology Facilities Council (STFC) ST/I001573/1
Science and Technology Facilities Council (STFC) ST/J003697/1
Leverhulme TrustUNSPECIFIED
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)32120009
International Fulbright Science and Technology AwardUNSPECIFIED
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)FONDECYT 1101024
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)Anillo ACT1101
Caltech NuSTAR subcontract44A-1092750
Swiss National Science Foundation (SNSF)PP00P2_138979/1
Subject Keywords: galaxies: active; X-rays: galaxies
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2014-62
Record Number:CaltechAUTHORS:20140606-142611348
Persistent URL:
Official Citation: NuSTAR Observations of Heavily Obscured Quasars at z ~ 0.5 G. B. Lansbury et al. 2014 ApJ 785 17
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46136
Deposited By: Ruth Sustaita
Deposited On:06 Jun 2014 22:07
Last Modified:31 Oct 2017 19:58

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