A long term study of AGN X-ray variability. Structure function analysis on a ROSAT-XMM quasar sample

Abstract

Variability in the X-rays is a key ingredient in understanding and unveiling active galactic nuclei (AGN) properties. In this band flux variations occur on short time scales (hours) as well as on larger times scales. While short time scale variability is often investigated in single source studies, only few works are able to explore flux variation on very long time scales.This work provides a statistical analysis of the AGN long term X-ray variability. We study variability on the largest time interval ever investigated for the 0.2-2 keV band, up to $\sim 20$ years rest-frame for a sample of 220 sources. Moreover, we study variability for 2,700 quasars up to $\sim 8$ years rest-frame in the same (soft) band.We build our source sample using the 3XMM serendipitous source catalogue data release 5, and data from ROSAT All Sky Survey Bright and Faint source catalogues. In order to select only AGN we use the Sloan Digital Sky Survey quasar catalogues data releases 7 and 12. Combining ROSAT and XMM-Newton observations, we investigate variability using the structure function analysis which describes the amount of variability as a function of the lag between the observations.Our work shows an increase of the structure function up to 20 years. We do not find evidence of a plateau in the structure function on these long time scales.The increase of the structure function at long time lags suggests that variability in the soft X-rays can be influenced by flux variations originated in the accretion disk or that they take place in a region large enough to justify variation on such long time scales.

7 pages, 7 figures, to appear on A&A, minor corrections for affiliations and language

References in corpus (43)

• The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release
• Active Galactic Nuclei as scaled-up Galactic black holes
• Intrinsic disc emission and the Soft X-ray Excess in AGN
• The XMM-Newton Serendipitous Survey. V. The Second XMM-Newton Serendipitous Source Catalogue
• The Sloan Digital Sky Survey Quasar Catalog: twelfth data release
• The diversity of quasars unified by accretion and orientation
• A Model for the X-Ray and UV Emission from Seyfert Galaxies and Galactic Black Holes
• The XMM-Newton serendipitous survey. VII. The third XMM-Newton serendipitous source catalogue
• Ubiquitous variability of X-ray absorbing column densities in Seyfert 2 Galaxies
• A Description of Quasar Variability Measured Using Repeated SDSS and POSS Imaging
• X-ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
• CAIXA: a Catalogue of AGN In the XMM-Newton Archive I. Spectral analysis
• CAIXA: a catalogue of AGN in the XMM-Newton archive III. Excess Variance Analysis
• First X-ray-Based Statistical Tests for Clumpy-Torus Models: Eclipse Events from 230 Years of Monitoring of Seyfert AGN
• Optical Variability in Active Galactic Nuclei: Starbursts or Disk Instabilities?
• Discovery of multiple Lorentzian components in the X-ray timing properties of the Narrow Line Seyfert 1 Ark 564
• X-ray absorption by Broad Line Region Clouds in Mrk 766
• Multiwavelength campaign on Mrk 509. IV. Optical-UV-X-ray variability and the nature of the soft X-ray excess
• The scaling of the X-ray variability with black hole mass in AGN
• On the size and location of the X-ray emitting coronae around black holes
• Structure Function Analysis of Long Term Quasar Variability
• Multiwavelength campaign on Mrk 509 XII. Broad band spectral analysis
• Quasar Optical Variability in the Palomar-QUEST Survey
• Rapid N_H changes in NGC 4151
• The relationship between X-ray variability amplitude and black hole mass in active galactic nuclei
• The Variability of Quasars. II. Frequency Dependence
• The Ensemble Variability Properties of Faint QSOs
• Tracing a Disk Wind in NGC 3516
• The existence of warm and optically thick dissipative coronae above accretion disks
• Variability Selected Low-Luminosity Active Galactic Nuclei in the 4 Ms Chandra Deep Field-South
• Ensemble X-ray variability of Active Galactic Nuclei. II. Excess Variance and updated Structure Function
• Multiwavelength campaign on Mrk 509. I. Variability and spectral energy distribution
• Ensemble X-ray variability of Active Galactic Nuclei from serendipitous source catalogues
• Long Term Variability of SDSS Quasars
• Detection of a high frequency break in the X-ray power spectrum of Ark 564
• Variability and the X-ray/UV ratio of active galactic nuclei. II. Analysis of a low-redshift Swift sample
• Size-Mass-luminosity relations in AGN and the role of the accretion disc
• X-ray Power Density Spectrum of the Narrow Line Seyfert 1 Galaxy Akn 564
• Variability and the X-ray/UV ratio of Active Galactic Nuclei
• The Long-Term X-Ray Variability of Broad Absorption Line Quasars
• Exploratory X-ray Monitoring of Luminous Radio-Quiet Quasars at High Redshift: Initial Results
• Highly variable AGN from the XMM-Newton Slew Survey
• The longest timescale X-ray variability reveals an evidence for active galactic nuclei in the high accretion state

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• Investigating the interplay between the coronal properties and the hard X-ray variability of active galactic nuclei with NuSTAR
• Probing the disk-corona systems and broad line regions of changing-look quasars with X-ray and optical observations
• The X-ray Variability of AGN and its Implications for Observations of Galaxy Clusters
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• Strong and Rapid X-ray Variability of the Super-Eddington Accreting Quasar SDSS J081456.10+532533.5
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• Highly Variable Active Galactic Nuclei in the SRG/eROSITA All-Sky Survey: I. Constructing Sample and Catalog of Sources Detected in Low State
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• The X-ray emission of the Seyfert 2 galaxy MCG-01-24-12
• The NuSTAR view of the Seyfert Galaxy HE 0436-4717
• Characterisation of the X-ray point source variability in the eROSITA south ecliptic pole field
• The eROSITA DR1 variability catalogue
• Magnetic Reconnection as a Potential Driver of X-ray Variability in Active Galactic Nuclei
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