The GALEX Time Domain Survey. II. Wavelength-Dependent Variability of Active Galactic Nuclei in the Pan-STARRS1 Medium Deep Survey

Abstract

We analyze the wavelength-dependent variability of a sample of spectroscopically confirmed active galactic nuclei (AGN) selected from near-UV ($NUV$) variable sources in the GALEX Time Domain Survey that have a large amplitude of optical variability (difference-flux S/N $>$ 3) in the Pan-STARRS1 Medium Deep Survey (PS1 MDS). By matching GALEX and PS1 epochs in 5 bands ($NUV$, $g_{P1}$, $r_{P1}$, $i_{P1}$, $z_{P1}$) in time, and taking their flux difference, we create co-temporal difference-flux spectral energy distributions ($\Delta f$SEDs) using two chosen epochs for each of the 23 objects in our sample on timescales of about a year. We confirm the "bluer-when-brighter" trend reported in previous studies, and measure a median spectral index of the $\Delta f$SEDs of ${\alpha }_{\lambda }$ = 2.1 that is consistent with an accretion disk spectrum. We further fit the $\Delta f$SEDs of each source with a standard accretion disk model in which the accretion rate changes from one epoch to the other. In our sample, 17 out of 23 ($\sim$74 %) sources are well described by this variable accretion-rate disk model, with a median average characteristic disk temperature ${\bar{T}}^{\ast }$ of $1.2\times 10^5$~K that is consistent with the temperatures expected given the distribution of accretion rates and black hole masses inferred for the sample. Our analysis also shows that the variable accretion rate model is a better fit to the $\Delta f$SEDs than a simple power law.

arXiv comment16 pages, 11 figures, Accepted for publication in The Astrophysical Journal September, 20, 2016

References in corpus (38)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Correcting for the Effects of Interstellar Extinction
• The Baryon Oscillation Spectroscopic Survey of SDSS-III
• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• A Catalog of Quasar Properties from SDSS DR7
• Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars
• The Pan-STARRS1 Photometric System
• The First Data Release of the Sloan Digital Sky Survey
• 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
• The Ensemble Photometric Variability of ~25000 Quasars in the Sloan Digital Sky Survey
• A Composite HST Spectrum of Quasars
• The UV-optical Galaxy Color-Magnitude Diagram I: Basic Properties
• Hectospec, the MMT's 300 Optical Fiber-Fed Spectrograph
• Cosmological Constraints from Measurements of Type Ia Supernovae discovered during the first 1.5 years of the Pan-STARRS1 Survey
• Space Telescope and Optical Reverberation Mapping Project. III. Optical Continuum Emission and Broad-Band Time Delays in NGC 5548
• Black Hole Growth to z = 2 - I: Improved Virial Methods for Measuring M_BH and L/L_Edd
• Testing LMC Microlensing Scenarios: The Discrimination Power of the SuperMACHO Microlensing Survey
• A Reverberation-Based Mass for the Central Black Hole in NGC 4151
• Quasar Accretion Disks Are Strongly Inhomogeneous
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Spectral Variability of Quasars in the Sloan Digital Sky Survey. I: Wavelength Dependence
• On the Thermal Stability of Radiation Dominated Accretion Disks
• Long term optical and X-ray variability of the Seyfert galaxy Markarian 79
• The Color Variability of Quasars
• Turbulent Stresses in Local Simulations of Radiation-Dominated Accretion Disks, and the Possibility of the LIghtman-Eardley Instability
• Characteristic QSO Accretion Disk Temperatures from Spectroscopic Continuum Variability
• Evidence for Large Temperature Fluctuations in Quasar Accretion Disks From Spectral Variability
• An accretion disc model for quasar optical variability
• The GALEX Time Domain Survey I. Selection and Classification of Over a Thousand UV Variable Sources
• The 2dF Galaxy Redshift Survey: constraints on cosmic star-formation history from the cosmic spectrum
• Statistical Properties of Multi-epoch Spectral Variability of SDSS Stripe82 Quasars
• Constraints on the temperature inhomogeneity in quasar accretion discs from the ultraviolet-optical spectral variability
• Ultraviolet Continuum Color Variability of Luminous Sloan Digital Sky Survey QSOs
• Stabilization of radiation pressure dominated accretion disks by viscous fluctuations
• Of Genes and Machines: application of a combination of machine learning tools to astronomy datasets
• Selection of Burst-like Transients and Stochastic Variables Using Multi-Band Image Differencing in the Pan-STARRS1 Medium-Deep Survey

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