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NuSTAR observations of heavily obscured quasars at z ~ 0.5.

Lansbury, G.B. and Alexander, D.M. and Del Moro, A. and Gandhi, P. and Assef, R.J. and Stern, D. and Aird, J. and Ballantyne, D.R. and Baloković, M. and Bauer, F.E. and Boggs, S.E. and Brandt, W.N. and Christensen, F.E. and Craig, W.W. and Elvis, M. and Grefenstette, B.W. and Hailey, C.J. and Harrison, F.A. and Hickox, R.C. and Koss, M. and LaMassa, S.M. and Luo, B. and Mullaney, J.R. and Teng, S.H. and Urry, C.M. and Zhang, W.W. (2014) 'NuSTAR observations of heavily obscured quasars at z ~ 0.5.', Astrophysical journal., 785 (1). p. 17.

Abstract

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 gsim 5 × 1023 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 gsim 1024 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
Keywords:Galaxies: active, X-rays: galaxies.
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1088/0004-637X/785/1/17
Publisher statement:© 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
Date accepted:No date available
Date deposited:05 August 2014
Date of first online publication:April 2014
Date first made open access:No date available

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