{
  "id": "1502.07353",
  "version": "v1",
  "published": "2015-02-25T21:00:13.000Z",
  "updated": "2015-02-25T21:00:13.000Z",
  "title": "Determining the covering factor of Compton-thick active galactic nuclei with NuSTAR",
  "authors": [
    "M. Brightman",
    "M. Balokovic",
    "D. Stern",
    "P. Arevalo",
    "D. R. Ballantyne",
    "F. E. Bauer",
    "S. E. Boggs",
    "W. W. Craig",
    "F. E. Christensen",
    "A. Comastri",
    "F. Fuerst",
    "P. Gandhi",
    "C. J. Hailey",
    "F. A. Harrison",
    "R. C. Hickox",
    "M. Koss",
    "S. LaMassa",
    "S. Puccetti",
    "E. Rivers",
    "R. Vasudevan",
    "D. J. Walton",
    "W. W. Zhang"
  ],
  "comment": "Accepted for publication in ApJ",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "The covering factor of Compton-thick obscuring material associated with the torus in active galactic nuclei (AGN) is at present best understood through the fraction of sources exhibiting Compton-thick absorption along the line of sight ($N_{H}>1.5\\times10^{24}$ cm$^{-2}$) in the X-ray band, which reveals the average covering factor. Determining this Compton-thick fraction is difficult however, due to the extreme obscuration. With its spectral coverage at hard X-rays ($>$10 keV), NuSTAR is sensitive to the AGN covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a spectral analysis of 10 AGN observed with NuSTAR where the obscuring medium is optically thick to Compton scattering, so called Compton-thick (CT) AGN. We use the torus models of Brightman & Nandra which 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 Compton-thick gas in these sources individually. Across the sample we find mild to heavy Compton-thick columns, with $N_{H}$ measured from $10^{24}-10^{26}$ cm$^{-2}$, and a wide range of covering factors, where individual measurements range from 0.2-0.9. We find that the covering factor, $f_{c}$, is a strongly decreasing function of the intrinsic 2-10 keV luminosity, $L_{X}$, where $f_{c}=(-0.41\\pm0.13)$log$_{10}$($L_{X}$/erg s$^{-1}$)$+18.31\\pm5.33$, across more than two orders of magnitude in $L_{X}$ (10$^{41.5}-10^{44}$ erg s$^{-1}$). The covering factors measured here agree well with the obscured fraction as a function of $L_{X}$ as determined by studies of local AGN with $L_{X}>10^{42.5}$ erg s$^{-1}$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-02-25T21:00:13.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "covering factor",
      "compton-thick active galactic nuclei",
      "sources exhibiting compton-thick absorption",
      "individual measurements range",
      "heavy compton-thick columns"
    ],
    "publication": {
      "doi": "10.1088/0004-637X/805/1/41"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1346473,
      "adsabs": "2015arXiv150207353B"
    }
  }
}