Long-term X-Ray Variability of Typical Active Galactic Nuclei in the Distant Universe
Journal
Date Issued
2016
Author(s)
Yang, G.
•
Brandt, W. N.
•
Luo, B.
•
Xue, Y. Q.
•
Bauer, F. E.
•
Sun, M. Y.
•
Kim, S.
•
Schulze, S.
•
Zheng, X. C.
•
•
Shemmer, O.
•
Liu, T.
•
Schneider, D. P.
•
Vignali, C.
•
•
Wang, J. -X.
Abstract
We perform long-term (≈15 years, observed-frame) X-ray variability analyses of the 68 brightest radio-quiet active galactic nuclei (AGNs) in the 6 Ms Chandra Deep Field-South survey; the majority are in the redshift range of 0.6-3.1, providing access to penetrating rest-frame X-rays up to ≈10-30 keV. Of the 68 sources, 24 are optical spectral type I AGNs, and the rest (44) are type II AGNs. The timescales 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}{{X}}) and absorption ({N}{{H}}) variability via spectral fitting. Most (74%) sources show {L}{{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 ≲0.3 pc. {L}{{X}} variability is also detected in a broad absorption line quasar. The {N}{{H}} variability amplitude for our sample appears to rise as time separation increases. About 16% of sources show {N}{{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.
Volume
831
Issue
2
Start page
145
Issn Identifier
0004-637X
Ads BibCode
2016ApJ...831..145Y
Rights
open.access
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