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J/ApJ/831/145        6Ms Chandra long-term analyses of AGNs        (Yang+, 2016)

Long-term X-ray variability of typical active galactic nuclei in the distant universe. 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. <Astrophys. J., 831, 145-145 (2016)> =2016ApJ...831..145Y (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; X-ray sources ; Surveys ; Redshifts Keywords: galaxies: active; galaxies: nuclei; methods: data analysis; quasars: general; X-rays: galaxies; X-rays: general 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 6Ms 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 ∼10-30keV. 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 (LX) and absorption (NH) variability via spectral fitting. Most (74%) sources show LX 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 ≲0.3pc. LX variability is also detected in a broad absorption line quasar. The NH variability amplitude for our sample appears to rise as time separation increases. About 16% of sources show NH 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. Description: This work is based on the Chandra CDF-S data. The observations were taken from 1999 October to 2015 January with a total observation time of 5.7Ms. In total, there are 84 observations utilized with median exposure time ∼60ks. All of the 84 observations were performed using the Advanced CCD Imaging Spectrometer imaging array (ACIS-I). See B. Luo et al. 2016, in prep (L16) for more observation details. Sixty-eight sources are selected with 649-11283 counts; the median number of counts is 1399. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 144 68 Source properties
See also: B/chandra : The Chandra Archive Log (CXC, 1999-2014) J/ApJS/224/15 : Improved 2Ms and 250ks Chandra catalogs (Xue+, 2016) J/ApJ/825/7 : Evolution of ∼6Ms CDF-S galaxies (Lehmer+, 2016) J/ApJ/819/62 : The COSMOS-Legacy Survey (CLS) catalog (Civano+, 2016) J/ApJ/808/184 : NuSTAR surveys: ECDF-S catalog (Mullaney+, 2015) J/A+A/579/A115 : SUDARE-VOICE variability-selection of AGN (Falocco+, 2015) J/A+A/564/A125 : AGN Torus model comparison of AGN in CDFS (Buchner+, 2014) J/A+A/563/A57 : Long-term variability of AGN at hard X-rays (Soldi+, 2014) J/MNRAS/436/3759 : ECDFS sources optical/IR counterparts (Bonzini+, 2013) J/A+A/555/A42 : The XMM-CDFS catalogues (Ranalli+, 2013) J/MNRAS/426/3334 : Australia Telescope Large Area Survey (Mao+, 2012) J/ApJ/748/124 : AGN X-ray variability in the 4Ms catalog (Young+, 2012) J/ApJ/746/54 : Chandra X-ray observations of SDSS-DR5 QSOs (Gibson+, 2012) J/A+A/542/A83 : CAIXA. II. AGNs from excess variance analysis (Ponti+, 2012) J/A+A/536/A84 : X-ray variability of AGN (Vagnetti+, 2011) J/ApJS/195/10 : The CDF-S survey: 4Ms source catalogs (Xue+, 2011) J/ApJ/726/20 : X-ray emission from quasars (Miller+, 2011) J/ApJS/191/124 : Optical spectrosc. of ECDF-S X-ray sources (Silverman+, 2010) J/ApJS/187/560 : Photometric redshifts of the 2Ms CDF-S (Luo+, 2010) J/ApJS/187/251 : Ultradeep Ks imaging in the GOODS-N (Wang+, 2010) J/ApJ/722/520 : Gamma-ray light curves of Fermi blazars (Abdo+, 2010) J/ApJ/698/740 : VLA survey of CDF-S. III. (Tozzi+, 2009) J/ApJ/693/1713 : Spectroscopy of X-ray sources in ECDF-S (Treister+, 2009) J/ApJ/692/758 : BAL QSOs in SDSS-DR5 (Gibson+, 2009) J/A+A/497/81 : Variability-selected AGN in CDFS (Boutsia+, 2009) J/ApJ/685/773 : X-ray-UV relations in SDSS DR5 QSOs (Gibson+, 2008) J/A+A/487/475 : X-ray variability of AGNs in Lockman Hole (Papadakis+, 2008) J/ApJ/657/116 : X-ray and UV parameters of radio-quiet quasars (Kelly+, 2007) J/A+A/465/1099 : Redshift catalog of 691 objects in CDFS (Ravikumar+, 2007) J/A+A/451/457 : X-ray properties of AGN in CDFS (Tozzi+, 2006) J/A+A/437/883 : K20 survey: spectroscopic catalogue (Mignoli+, 2005) J/ApJS/155/271 : CDF-South: Optical spectroscopy (Szokoly+, 2004) J/MNRAS/328/150 : KX redshift survey (Croom+, 2001) Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 16 A16 --- Name Standard Chandra CDF-S source identifier 18- 25 F8.5 deg RAdeg Right Ascension in decimal degrees (J2000) 27- 35 F9.5 deg DEdeg Declination in decimal degrees (J2000) 37- 40 F4.2 --- z [0.1/3.8] Adopted redshift (1) 42- 45 F4.2 --- e_z [0.01/0.3]? The 1σ error in z (2) 47- 49 A3 --- OType Optical spectral type (3) 51- 54 F4.2 arcmin Off [1.9/8] Off-axis angle 56- 62 F7.1 ct Cts [648/11284] Full band, 0.5-7keV, total net counts; not aperture corrected 64- 68 F5.2 % pPF [0/86] Photon-flux variability p-value 70- 74 F5.2 % pHR [0/100] Hardness-ratio variability p-value 76- 78 F3.1 keV Epeg [0.5/2.7] Lower end of normalization band (4) 80- 83 F4.1 % Good [0/44] Goodness of the spectral fitting (5) 85- 88 F4.2 --- Gamma [1/3] Power-law photon index 90- 97 E8.2 10-7W Lx Epoch-mean, intrinsic luminosity, rest-frame 2-10keV; erg/s 99-106 E8.2 cm-2 NH Epoch-mean, Hydrogen column density 108-113 F6.1 --- DelAICL [-6/1060] Metric of Lx variability significance (6) 115-118 F4.1 --- DelAICN [-6/84] Metric of NH variability significance (6) 120-125 F6.3 --- sigma2L [-0.02/0.5] Normalized excess variance of LX variability (6) 127-131 F5.3 --- e_sigma2L [0.001/0.3] Uncertainty in sigma2L 133-138 F6.3 --- sigma2N [-0.05/0.2]? Normalized excess variance of NH variability (7) 140-144 F5.3 --- e_sigma2N [0.001/0.2]? Uncertainty in sigma2N
Note (1): See B. Luo et al. 2016, in prep (L16) for redshift references. Note (2): A blank indicates a spectroscopic redshift has been used (55 zspec). Note (3): See Section 2.2 for the classification scheme. Is (IIs): type I (II) from spectral classification; Ic (IIc): type I (II) from color classification. The spectral classifications are from: Szokoly et al. (2004, J/ApJS/155/271); Mignoli et al. (2005, J/A+A/437/883); Ravikumar et al. (2007, J/A+A/465/1099); Tozzi et al. (2009, J/ApJ/698/740); Treister et al. (2009, J/ApJ/693/1713); Silverman et al. (2010, J/ApJS/191/124); Mao et al. (2012, J/MNRAS/426/3334). Note (4): Used in pegpwrlw (Appendix A). Note (5): Goodness of the spectral fitting (wabs x zwabs x pegpwrlw model) (see Section 3.2.1). Note (6): See Section 3.2.3. Note (7): See Section 3.2.5. We only calculated this quantity for the 35 sources with all four epochs having δNH,i/NH,i<0.4 (see Appendix A); blanks indicates the other 33 sources.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Feb-2017
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