The Timescale-Dependent Color Variability of Quasars Viewed with GALEX

Abstract

In recent work done by Sun et. al., the color variation of quasars, namely the bluer-when-brighter trend, was found to be timescale-dependent using SDSS $g/r$ band light curves in the Stripe 82. Such timescale dependence, i.e., bluer variation at shorter timescales, supports the thermal fluctuation origin of the UV/optical variation in quasars, and can be well modeled with the inhomogeneous accretion disk model. In this paper, we extend the study to much shorter wavelengths in the rest frame (down to extreme UV), using GALaxy Evolution eXplorer (GALEX) photometric data of quasars collected in two ultraviolet bands (near-UV and far-UV). We develop Monte-Carlo simulations to correct possible biases due to the considerably larger photometric uncertainties in GALEX light curves (particularly in far-UV, comparing with SDSS $g/r$ bands), which otherwise could produce artificial results. We securely confirm the previously discovered timescale dependence of the color variability with independent datasets and at shorter wavelengths. We further find the slope of the correlation between the amplitude of color variation and timescale however appears even steeper than that predicted by the inhomogeneous disk model, which assumes that disk fluctuations follow damped random walk process. In line with the much flatter structure function observed in far-UV comparing with that at longer wavelengths, this implies deviation from DRW process in the inner disk where rest frame extreme UV radiation is produced.

arXiv comment8 pages, 6 figures. Accepted by APJ

References in corpus (56)

• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
• A Catalog of Quasar Properties from SDSS DR7
• The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release
• Are the Variations in Quasar Optical Flux Driven by Thermal Fluctuations?
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• Active Galactic Nuclei as scaled-up Galactic black holes
• The Ensemble Photometric Variability of ~25000 Quasars in the Sloan Digital Sky Survey
• Measuring the broadband power spectra of active galactic nuclei with RXTE
• The X-ray to optical-UV luminosity ratio of X-ray selected Type 1 AGN in XMM-COSMOS
• Combined Long and Short Timescale X-ray Variability of NGC4051 with RXTE and XMM-Newton
• Quantifying Quasar Variability As Part of a General Approach To Classifying Continuously Varying Sources
• Is Quasar Optical Variability a Damped Random Walk?
• Space Telescope and Optical Reverberation Mapping Project. III. Optical Continuum Emission and Broad-Band Time Delays in NGC 5548
• Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548
• Long-term optical variability properties of the Palomar-Green quasars
• The Simultaneous Optical-to-X-ray Spectral Energy Distribution of Soft X-ray Selected AGN observed by Swift
• Flexible and Scalable Methods for Quantifying Stochastic Variability in the Era of Massive Time-Domain Astronomical Data Sets
• X-ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
• Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei
• Soft X-ray and Ultraviolet Emission Relations in Optically Selected AGN Samples
• Optical Variability in Active Galactic Nuclei: Starbursts or Disk Instabilities?
• Quasar Accretion Disks Are Strongly Inhomogeneous
• Space Telescope and Optical Reverberation Mapping Project. I. Ultraviolet Observations of the Seyfert 1 Galaxy NGC 5548 with the Cosmic Origins Spectrograph on Hubble Space Telescope
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Quasars and the Big Blue Bump
• Revisiting Stochastic Variability of AGNs with Structure Functions
• Spectral Variability of Quasars in the Sloan Digital Sky Survey. I: Wavelength Dependence
• The Variability of Quasars. II. Frequency Dependence
• The correlations between optical variability and physical parameters of quasars in SDSS Stripe 82
• Anatomy of the AGN in NGC 5548: II. The Spatial, Temporal and Physical Nature of the Outflow from HST/COS Observations
• The Color Variability of Quasars
• Quasar Spectral Slope Variability in the Optical Band
• Characteristic QSO Accretion Disk Temperatures from Spectroscopic Continuum Variability
• Spectral variability of quasars from multi-epoch photometric data in the Sloan Digital Sky Survey Stripe 82
• Evidence for Large Temperature Fluctuations in Quasar Accretion Disks From Spectral Variability
• The UV peak in Active Galactic Nuclei : a false continuum from blurred reflection ?
• The Galaxy Evolution Explorer (GALEX). Its legacy of UV surveys, and science highlights
• An accretion disc model for quasar optical variability
• The Discovery of Timescale-Dependent Color Variability of Quasars
• Long-Term Optical Continuum Color Variability of Nearby Active Galactic Nuclei
• A DECam Search for an Optical Counterpart to the LIGO Gravitational Wave Event GW151226
• A Degeneracy in DRW Modelling of AGN Light Curves
• GALEX observations of quasar variability in the ultraviolet
• Statistical Properties of Multi-epoch Spectral Variability of SDSS Stripe82 Quasars
• Correlated X-ray/Ultraviolet/Optical Variability in NGC 6814
• Simulating the timescale dependent color variation in quasars with a revised inhomogeneous disk model
• Variability of accretion flow in the core of the Seyfert galaxy NGC 4151
• Ultraviolet variability of quasars: dependence on the accretion rate
• Continuum Variability of Active Galactic Nuclei in the Optical-UV Range
• The optical variability of SDSS quasars from multi-epoch spectroscopy. II. color variation
• Ultraviolet Continuum Color Variability of Luminous Sloan Digital Sky Survey QSOs
• Colour changes in quasar light curves
• The Second Galex Ultraviolet Variability (GUVV-2) Catalog
• The Ultraviolet/optical variability of steep-spectrum radio quasars: the change in accretion rate ?
• The First Hard X-Ray Power Spectral Density Functions of AGN
• Spectral variability of FIRST bright QSOs with SDSS observations

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• EUCLIA - Exploring the UV/optical continuum lag in active galactic nuclei. I. a model without light echoing
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• Short time-scale optical variability properties of the largest AGN sample observed with Kepler/K2
• EUCLIA. II. On the puzzling large UV to X-ray lags in Seyfert galaxies
• Evolution of quasar stochastic variability along its main sequence
• Modelling the Multiwavelength Variability of Mrk 335 using Gaussian Processes
• Extreme Variability Quasars in Their Various States. I: The sample selection and composite SDSS spectra
• Correlation between Optical and UV Variability of Quasars
• On the UV/optical variation in NGC 5548: new evidence against the reprocessing diagram
• An intrinsic link between long-term UV/optical variations and X-ray loudness in quasars
• How can the optical variation properties of active galactic nuclei be unbiasedly measured?
• More than softer-when-brighter: the X-Ray powerlaw spectral variability in NGC 4051
• A new timescale-mass scaling for the optical variation of active galactic nuclei across the intermediate-mass to supermassive scales
• New Clues to Jet Launching: The inner disks in radio loud quasars may be more stable
• The Relation between X-ray and Ultraviolet Variability of Quasars
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