{
  "id": "1608.08224",
  "version": "v1",
  "published": "2016-08-29T20:00:11.000Z",
  "updated": "2016-08-29T20:00:11.000Z",
  "title": "Long-Term X-ray Variability of Typical Active Galactic Nuclei in the Distant Universe",
  "authors": [
    "G. Yang",
    "W. Brandt",
    "B. Luo",
    "Y. Xue",
    "F. Bauer",
    "M. Sun",
    "S. Kim",
    "S. Schulze",
    "X. Zheng",
    "M. Paolillo",
    "O. Shemmer",
    "T. Liu",
    "D. Schneider",
    "C. Vignali",
    "F. Vito",
    "J. -X. Wang"
  ],
  "comment": "21 pages, 17 figures, accepted for publication in ApJ",
  "categories": [
    "astro-ph.HE",
    "astro-ph.GA",
    "astro-ph.IM"
  ],
  "abstract": "We perform long-term ($\\approx 15$ yr, observed-frame) X-ray variability analyses of the 68 brightest radio-quiet active galactic nuclei (AGNs) in the 6 Ms $Chandra$ Deep Field-South (CDF-S) survey; the majority are in the redshift range of $0.6-3.1$, providing access to penetrating rest-frame X-rays up to $\\approx 10-30$ keV. Twenty-four of the 68 sources are optical spectral type I AGNs, and the rest (44) are type II AGNs. The time scales probed in this work are among the longest for X-ray variability studies of distant AGNs. Photometric analyses reveal widespread photon-flux variability: $90\\%$ of AGNs are variable above a 95% confidence level, including many X-ray obscured AGNs and several optically classified type II quasars. We characterize the intrinsic X-ray luminosity ($L_{\\rm{X}}$) and absorption ($N_{\\rm{H}}$) variability via spectral fitting. Most (74%) sources show $L_{\\rm{X}}$ variability; the variability amplitudes are generally smaller for quasars. A Compton-thick candidate AGN shows variability of its high-energy X-ray flux, indicating the size of reflecting material to be $\\lesssim 0.3$ pc. $L_{\\rm{X}}$ variability is also detected in a broad absorption line (BAL) quasar. The $N_{\\rm{H}}$ variability amplitude for our sample appears to rise as time separation increases. About 16% of sources show $N_{\\rm{H}}$ variability. One source transitions from an X-ray unobscured to obscured state while its optical classification remains type I; this behavior indicates the X-ray eclipsing material is not large enough to obscure the whole broad-line region.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-08-29T20:00:11.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "typical active galactic nuclei",
      "long-term x-ray variability",
      "distant universe",
      "radio-quiet active galactic nuclei",
      "analyses reveal widespread photon-flux variability"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 21,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}