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Determining the Covering Factor of Compton-Thick Active Galactic Nuclei with NuSTARThe covering factor of Compton-thick (CT) obscuring material associated with the torus in active galactic nuclei (AGNs) is at present best understood through the fraction of sources exhibiting CT absorption along the line of sight (N(sub H) greater than 1.5 x 10(exp 24) cm(exp −2)) in the X-ray band, which reveals the average covering factor. Determining this CT fraction is difficult, however, due to the extreme obscuration. With its spectral coverage at hard X-rays (greater than 10 keV), Nuclear Spectroscopic Telescope Array (NuSTAR) is sensitive to the AGNs covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a spectral analysis of 10 AGNs observed with NuSTAR where the obscuring medium is optically thick to Compton scattering, so-called CT AGNs. We use the torus models of Brightman and Nandra that predict the X-ray spectrum from reprocessing in a torus and include the torus opening angle as a free parameter and aim to determine the covering factor of the CT gas in these sources individually. Across the sample we find mild to heavy CT columns, with N(sub H) measured from 10(exp 24) to 10(exp 26) cm(exp −2), and a wide range of covering factors, where individual measurements range from 0.2 to 0.9. We find that the covering factor, f(sub c), is a strongly decreasing function of the intrinsic 2-10 keV luminosity, L(sub X), where f(sub c) = (−0.41 +/- 0.13)log(sub 10)(L(sub X)/erg s(exp −1))+18.31 +/- 5.33, across more than two orders of magnitude in L(sub X) (10(exp 41.5) - 10(exp 44) erg s(exp −1)). The covering factors measured here agree well with the obscured fraction as a function of LX as determined by studies of local AGNs with L(sub X) greater than 10(exp 42.5) erg s(exp −1).
Document ID
20160010531
Document Type
Reprint (Version printed in journal)
Authors
Brightman, M. (California Inst. of Tech. Pasadena, CA, United States)
Balokovic, M. (California Inst. of Tech. Pasadena, CA, United States)
Stern, D. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Arevalo, P. (Valparaiso Univ. Vina del Mar, Chile)
Ballantyne, D. R. (Georgia Inst. of Tech. Atlanta, GA, United States)
Bauer, F. E. (Universidad Catolica de Chile Santiago, Chile)
Boggs, S. E. (California Univ. Berkeley, CA, United States)
Craig, W. W. (California Univ. Berkeley, CA, United States)
Christensen, F. E. (Technical Univ. of Denmark Lyngby, Denmark)
Zhang, W. W. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 23, 2016
Publication Date
May 19, 2015
Publication Information
Publication: The Astrophysical Journal
Volume: 805
Issue: 1
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN35028
Funding Number(s)
CONTRACT_GRANT: NSF-AST-1008067
CONTRACT_GRANT: NNG08FD60C
CONTRACT_GRANT: ACT1101-IC120009
CONTRACT_GRANT: ST/J003697/1
CONTRACT_GRANT: PFB-06/2007
CONTRACT_GRANT: NNX14AQ07H
CONTRACT_GRANT: SNSF-PZ00P2-154799/1
CONTRACT_GRANT: FONDECYT-1141218
Distribution Limits
Public
Copyright
Other
Keywords
NGC 4945
Circinus) aEuro" X-rays: galaxies
NGC 1068
active aEuro" galaxies: individual (NGC 424