The XMM deep survey in the CDF-S. X. X-ray variability of bright sources

Abstract

We aim to study the variability properties of bright hard X-ray selected Active Galactic Nuclei (AGN) with redshift between 0.3 and 1.6 detected in the Chandra Deep Field South (XMM-CDFS) by a long XMM observation. Taking advantage of the good count statistics in the XMM CDFS we search for flux and spectral variability using the hardness ratio techniques. We also investigated spectral variability of different spectral components. The spectra were merged in six epochs (defined as adjacent observations) and in high and low flux states to understand whether the flux transitions are accompanied by spectral changes. The flux variability is significant in all the sources investigated. The hardness ratios in general are not as variable as the fluxes. Only one source displays a variable HR, anti-correlated with the flux (source 337). The spectral analysis in the available epochs confirms the steeper when brighter trend consistent with Comptonisation models only in this source. Finding this trend in one out of seven unabsorbed sources is consistent, within the statistical limits, with the 15 % of unabsorbed AGN in previous deep surveys. No significant variability in the column densities, nor in the Compton reflection component, has been detected across the epochs considered. The high and low states display in general different normalisations but consistent spectral properties. X-ray flux fluctuations are ubiquitous in AGN. In general, the significant flux variations are not associated with a spectral variability: photon index and column densities are not significantly variable in nine out of the ten AGN over long timescales (from 3 to 6.5 years). The photon index variability is found only in one source (which is steeper when brighter) out of seven unabsorbed AGN. These results are consistent with previous deep samples.

arXiv comment14 pages, 11 figures. Accepted in A&A

References in corpus (46)

• Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Advection-Dominated Accretion and the Spectral States of Black Hole X-Ray Binaries: Application to Nova Muscae 1991
• On characterising the variability properties of X-ray light curves from active galaxies
• Active Galactic Nuclei as scaled-up Galactic black holes
• Intrinsic disc emission and the Soft X-ray Excess in AGN
• The Chandra Deep Field South: Optical Spectroscopy I
• The Chandra Deep Field-South Survey: 7 Ms Source Catalogs
• X-ray Spectral Variability and Rapid Variability of the Soft X-ray Spectrum Seyfert 1 Galaxies Ark 564 and Ton S180
• GRS 1915+105 and the Disc-Jet Coupling in Accreting Black Hole Systems
• Ubiquitous variability of X-ray absorbing column densities in Seyfert 2 Galaxies
• Bayesian Estimation of Hardness Ratios: Modeling and Computations
• Correlation between Compton reflection and X-ray slope in Seyferts and X-ray binaries
• A unified model for the spectral variability in GRS 1915+105
• Correlations between X-ray and radio spectral properties of accreting black holes
• Multiwavelength observations of short time-scale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
• On X-ray Variability in Seyfert Galaxies
• Relativistic iron K X-ray Reverberation in NGC 4151
• The long term X-ray spectral variability of AGN
• The Extended Chandra Deep Field-South Survey: Optical spectroscopy of faint X-ray sources with the VLT and Keck
• The XMM Deep survey in the CDFS I. First results on heavily obscured AGN
• Optical Spectroscopy of X-ray sources in the Extended Chandra Deep Field South
• Prevalence of X-ray variability in the Chandra Deep Field South
• XMM-Newton observations of the Lockman Hole V: time variability of the brightest AGN
• The XMM deep survey in the CDFS IV. Candidate Compton-thick AGN
• Long-Term X-ray Variability of Typical Active Galactic Nuclei in the Distant Universe
• AGN X-ray variability in the XMM-COSMOS survey
• Tracing the accretion history of supermassive Black Holes through X-ray variability: results from the Chandra Deep Field-South
• X-ray variability in a deep, flux limited sample of QSOs
• Ensemble X-ray variability of Active Galactic Nuclei. II. Excess Variance and updated Structure Function
• Variability Selected Low-Luminosity Active Galactic Nuclei in the 4 Ms Chandra Deep Field-South
• The X-Ray Variability of a Large, Serendipitous Sample of Spectroscopic Quasars
• Measuring X-ray variability in faint/sparsely-sampled AGN
• A long term study of AGN X-ray variability. Structure function analysis on a ROSAT-XMM quasar sample
• Chandra monitoring of UGC 4203: the structure of the X-ray absorber
• X-ray spectral variability of the Seyfert galaxy NGC 4051
• Average Fe K-alpha emission from distant AGN
• Fe K emission from active galaxies in the COSMOS field
• Search for X-ray occultations in Active Galactic Nuclei
• Exploratory X-ray Monitoring of Luminous Radio-Quiet Quasars at High Redshift: Initial Results
• The XMM deep survey in the CDF-S. IX. An X-ray outflow in a luminous obscured quasar at z~1.6
• The X-ray Properties of the Nearby Star-Forming Galaxy IC 342: The XMM-Newton View
• A correlation between the spectral and timing properties of AGN
• Quasar spectral variability from the XMM-Newton serendipitous source catalogue
• Unveiling the physics of low luminosity AGN through X-ray variability: LINER versus Seyfert 2
• Rapid N_H Changes in NGC 4151
• The XMM deep survey in the CDF-S VIII. X-ray properties of the two brightest sources

Cited by in corpus (5)

• The XMM-SERVS survey: new XMM-Newton point-source catalog for the XMM-LSS field
• Unveiling sub-parsec supermassive black hole binary candidates in active galactic nuclei
• The XMM deep survey in the CDFS XI. X-ray properties of 185 bright sources
• The lively accretion disk in NGC 2992. II. The 2019/2021 X-ray monitoring campaigns
• X-ray Unveiling Events in a z~1.6 Active Galactic Nucleus in the 7 Ms Chandra Deep Field-South