Long-term X-ray variability of typical active galactic nuclei in the distant universe

G. Yang, W. N. Brandt, B. Luo, Y. Q. Xue, F. E. Bauer, M. Y. Sun, S. Kim, S. Schulze, X. C. Zheng, M. Paolillo, O. Shemmer, T. Liu, D. P. Schneider, C. Vignali, F. Vito, J. X. Wang

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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 () and absorption () variability via spectral fitting. Most (74%) sources show 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. variability is also detected in a broad absorption line quasar. The variability amplitude for our sample appears to rise as time separation increases. About 16% of sources show 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.

Original languageEnglish (US)
Article number145
JournalAstrophysical Journal
Volume831
Issue number2
DOIs
StatePublished - Nov 10 2016

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Yang, G., Brandt, W. N., Luo, B., Xue, Y. Q., Bauer, F. E., Sun, M. Y., Kim, S., Schulze, S., Zheng, X. C., Paolillo, M., Shemmer, O., Liu, T., Schneider, D. P., Vignali, C., Vito, F., & Wang, J. X. (2016). Long-term X-ray variability of typical active galactic nuclei in the distant universe. Astrophysical Journal, 831(2), [145]. https://doi.org/10.3847/0004-637X/831/2/145