A DESCRIPTION OF QUASAR VARIABILITY MEASURED USING REPEATED SDSS AND POSS IMAGING

By C. MacLeod, Željko Ivezic´, B. Sesar, W. de Vries, C. Kochanek, B. Kelly, A. Becker, Robert Lupton, P. Hall, Gordon Richards and 2 more. 2011

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We provide a quantitative description and statistical interpretation of the optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS) has obtained repeated imaging in five UV-to-IR photometric bands for 33,881 spectroscopically confirmed quasars. About 10,000 quasars have an average of 60 observations in each band obtained over a decade along Stripe 82 (S82), whereas the remaining ∼25,000 have 2–3 observations due to scan overlaps. The observed time lags span the range from a day to almost 10 years, and constrain quasar variability at rest-frame time lags of up to 4 years, and at rest-frame wavelengths from 1000 Å to 6000 Å. We publicly release a user-friendly catalog of quasars from the SDSS Data Release 7 that have been observed at least twice in SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it to analyze the ensemble properties of quasar variability. Based on a damped random walk (DRW) model defined by a characteristic timescale and an asymptotic variability amplitude that scale with the luminosity, black hole mass, and rest wavelength for individual quasars calibrated in S82, we can fully explain the ensemble variability statistics of the non-S82 quasars such as the exponential distribution of large magnitude changes. All available data are consistent with the DRW model as a viable description of the optical continuum variability of quasars on timescales of ∼5–2000 days in the rest frame. We use these models to predict the incidence of quasar contamination in transient surveys such as those from the Palomar Transient Factory and Large Synoptic Survey Telescope.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ca0e9376026b69c894791e422d0347cdd6be0017

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Citations in the corpus

• THE ULTRAVIOLET-BRIGHT, SLOWLY DECLINING TRANSIENT PS1-11af AS A PARTIAL TIDAL DISRUPTION EVENT (2013, background): “The characteristic amplitude of quasar photometric variability on these timescales is only ∼0.1 mag, with the amplitude of variability increasing on longer timescales (e.g., Webb & Malkan 2000; MacLeod et al. 2012a).”
• The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry (2017, methodology): “The DRW model is observed to be a good description of quasar variability within the time regime relevant to our study (e.g., Kelly et al. 2009; Koz lowski et al. 2010; Koz lowski 2016; MacLeod et al. 2010, 2012), and so is an effective prior to describe the light curve between observations.”
• REVERBERATION MEASUREMENTS OF THE INNER RADIUS OF THE DUST TORUS IN 17 SEYFERT GALAXIES (2014, background): “…UV-optical continuum emission, which has been demonstrated to be a good statistical model for AGN variability (e.g., Kelly et al. 2009; Koz lowski et al. 2010; MacLeod et al. 2010, 2012; Zu et al. 2013), and also assumes a top hat transfer function in the transfer equation of reverberation mapping.”
• THE MAN BEHIND THE CURTAIN: X-RAYS DRIVE THE UV THROUGH NIR VARIABILITY IN THE 2013 ACTIVE GALACTIC NUCLEUS OUTBURST IN NGC 2617 (2013, methodology): “We can now quantify quasar variability well, using the DRW model (e.g. Kelly et al. 2009, Kozłowski et al. 2010, MacLeod et al. 2010, MacLeod et al. 2012, Zu et al. 2013b) and the parameters of the DRW model are correlated with properties of the AGN.”
• A systematic search for changing-look quasars in SDSS (2015, methodology): “In addition to the DR8 photometry provided on the SDSS website, our analysis utilizes the S82 database of quasars in MacLeod et al. (2012), which includes observations taken in nonphotometric conditions and recalibrated using the improved method of Ivezić et al. (2004b).”
• COMPARING SINGLE-EPOCH VIRIAL BLACK HOLE MASS ESTIMATORS FOR LUMINOUS QUASARS (2012, background): “This absolute flux calibration neglects the continuum variability between the 2MASS and (spectroscopic) SDSS epochs, which is typically at the level of∼ 0.1 mag for average SDSS quasars (e.g., Sesar et al. 2007; MacLeod et al. 2011).”
• THE STRUCTURE OF THE BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI. I. RECONSTRUCTED VELOCITY-DELAY MAPS (2012, methodology): “This method models the continuum with a damped random walk (DRW) model that has been demonstrated to be a good statistical model of AGN variability (e.g., Kelly et al. 2009; Koz lowski et al. 2010; MacLeod et al. 2010; MacLeod et al. 2012; Zu et al. 2012).”
• Now You See It, Now You Don't: The Disappearing Central Engine of the Quasar J1011+5442 (2015, background): “It is not unusual to see variability in a quasar light curve; variability on the order of tenths of a magnitude is typical for quasars on timescales of a year (e.g., MacLeod et al. 2012).”