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The NuSTAR extragalactic surveys : X-ray spectroscopic analysis of the bright hard-band selected sample.

Zappacosta, L. and Comastri, A. and Civano, F. and Puccetti, S. and Fiore, F. and Aird, J. and Moro, A. Del and Lansbury, G. B. and Lanzuisi, G. and Goulding, A. and Mullaney, J. R. and Stern, D. and Ajello, M. and Alexander, D. M. and Ballantyne, D. R. and Bauer, F. E. and Brandt, W. N. and Chen, C.-T. J. and Farrah, D. and Harrison, F. A. and Gandhi, P. and Lanz, L. and Masini, A. and Marchesi, S. and Ricci, C. and Treister, E. (2018) 'The NuSTAR extragalactic surveys : X-ray spectroscopic analysis of the bright hard-band selected sample.', Astrophysical journal., 854 (1). p. 33.

Abstract

We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S 8 24 keV 7 10 = ´ -14 (– ) erg s cm - - 1 2 in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z = 0 2.1 – (median ázñ = 0.58). The spectral analysis is performed over the broad 0.5–24 keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at >10 keV to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density (NH), reflection parameter (R), and 10–40 keV luminosity (LX). Heavily obscured (log cm 2 NH 3 [ ] -2  ) and Compton-thick (CT; log cm 24 NH [ ] -2  ) AGN constitute ∼25% (15–17 sources) and ∼2–3% (1–2 sources) of the sample, respectively. The observed NH distribution agrees fairly well with predictions of cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of NH, accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to log cm 20 2 NH 4 [ ]– -2 = AGN is poorly constrained, formally in the range 2–56% (90% upper limit of 66%). We derived a fraction ( fabs) of obscured AGN (log cm 22 2 NH 4 [ ]– -2 = ) as a function of LX in agreement with CXBPSM and previous z < 1 X-ray determinations. Furthermore, fabs at z = 0.1 0.5 – and log erg s 43.6 44. Lx 3 ( )– -1 » agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of R with LX (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.3847/1538-4357/aaa550
Publisher statement:© 2018. The American Astronomical Society. All rights reserved.
Date accepted:29 December 2017
Date deposited:01 March 2018
Date of first online publication:08 February 2018
Date first made open access:01 March 2018

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