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  1. OA@INAF
  2. PRODOTTI RICERCA INAF
  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
  4. 1.01 Articoli in rivista
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/29246
Title: Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South
Authors: Ding, N.
Luo, B.
Brandt, W. N.
Paolillo, Maurizio 
Yang, G.
Lehmer, B. D.
Shemmer, O.
Schneider, D. P.
TOZZI, Paolo 
Xue, Y. Q.
Zheng, X. C.
Gu, Q. S.
Koekemoer, A. M.
Vignali, C.
Vito, F.
Wang, J. X.
Issue Date: 2018
Journal: THE ASTROPHYSICAL JOURNAL 
Number: 868
Issue: 2
First Page: 88
Abstract: In deep X-ray surveys, active galactic nuclei (AGNs) with a broad range of luminosities have been identified. However, cosmologically distant low-luminosity AGN (LLAGN, {L}<SUB>{{X</SUB>}}≲ {10}<SUP>42</SUP> erg s<SUP>-1</SUP>) identification still poses a challenge because of significant contamination from host galaxies. Based on the 7 Ms Chandra Deep Field-South (CDF-S) survey, the longest-timescale (∼17 years) deep X-ray survey to date, we utilize an X-ray variability selection technique to search for LLAGNs that remain unidentified among the CDF-S X-ray sources. We find 13 variable sources from 110 unclassified CDF-S X-ray sources. Except for one source that could be an ultraluminous X-ray source, the variability of the remaining 12 sources is most likely due to accreting supermassive black holes. These 12 AGN candidates have low intrinsic X-ray luminosities, with a median value of 7 × 10<SUP>40</SUP> erg s<SUP>-1</SUP>. They are generally not heavily obscured, with an average effective power-law photon index of 1.8. The fraction of variable AGNs in the CDF-S is independent of X-ray luminosity and is only restricted by the total number of observed net counts, confirming previous findings that X-ray variability is a near-ubiquitous property of AGNs over a wide range of luminosities. There is an anticorrelation between X-ray luminosity and variability amplitude for high-luminosity AGNs, but as the luminosity drops to ≲10<SUP>42</SUP> erg s<SUP>-1</SUP>, the variability amplitude no longer appears dependent on the luminosity. The entire observed luminosity-variability trend can be roughly reproduced by an empirical AGN variability model based on a broken power-law power spectral density function.
URI: http://hdl.handle.net/20.500.12386/29246
URL: https://arxiv.org/abs/1810.09465
https://iopscience.iop.org/article/10.3847/1538-4357/aaea60
ISSN: 0004-637X
DOI: 10.3847/1538-4357/aaea60
Bibcode ADS: 2018ApJ...868...88D
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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