ARE THE VARIATIONS IN QUASAR OPTICAL FLUX DRIVEN BY THERMAL FLUCTUATIONS?

By B. Kelly, J. Bechtold, Aneta Siemiginowska. 2009

430 citations recorded by the source corpus.

We analyze a sample of optical light curves for 100 quasars, 70 of which have black hole mass estimates. Our sample is the largest and broadest used yet for modeling quasar variability. The sources in our sample have z < 2.8, 1042 ≲ λLλ(5100 Å) ≲ 1046, and 106 ≲ MBH/M☉ ≲ 1010. We model the light curves as a continuous time stochastic process, providing a natural means of estimating the characteristic timescale and amplitude of quasar variations. We employ a Bayesian approach to estimate the characteristic timescale and amplitude of flux variations; our approach is not affected by biases introduced from discrete sampling effects. We find that the characteristic timescales strongly correlate with black hole mass and luminosity, and are consistent with disk orbital or thermal timescales. In addition, the amplitude of short-timescale variations is significantly anticorrelated with black hole mass and luminosity. We interpret the optical flux fluctuations as resulting from thermal fluctuations that are driven by an underlying stochastic process, such as a turbulent magnetic field. In addition, the intranight variations in optical flux implied by our empirical model are ≲0.02 mag, consistent with current microvariability observations of radio-quiet quasars. Our stochastic model is therefore able to unify both long- and short-timescale optical variations in radio-quiet quasars as resulting from the same underlying process, while radio-loud quasars have an additional variability component that operates on timescales ≲1 day.

View Paper: https://www.semanticscholar.org/paper/038a0ef9c888153d70e4f2c7ea5d7596d2e430f6

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Citations in the corpus

• The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry (2017, methodology): “JAVELIN and CREAM also use a a damped random walk (DRW) model for the variability, matching observations (e.g. Kelly et al. 2009; Koz lowski et al. 2010; MacLeod 6 et al. 2010).”
• 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).”
• 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): “For example, Kelly et al. (2009) argue that the DRW time scale could be related to the thermal time scale of the disk, while MacLeod et al. (2010) note that the scalings of both the DRW time scale and amplitude with wavelength, black hole mass, and luminosity all seem too weak compared to the…”
• THE SLOAN DIGITAL SKY SURVEY REVERBERATION MAPPING PROJECT: TECHNICAL OVERVIEW (2014, methodology): “In addition, alternative lag measurements to the simple CCF method, such as the Zu et al. (2011) method based on DRW models (e.g., Kelly et al. 2009), can in principle provide a more robust confidence estimation of the detected CCF peaks, and therefore reduce false detections.”
• Explaining changing-look AGN with state transition triggered by rapid mass accretion rate drop (2018, background): “The thermal timescale in particular is suggested as the origin of the 10–20% stochastic optical variability which is typically seen in AGNs on timescales of months (e.g., Kelly et al. 2009; MacLeod et al. 2010).”
• A systematic search for close supermassive black hole binaries in the Catalina Real-time Transient Survey (2015, methodology): “The magnitude X(t) at a given timestep ∆t from a previous value X(t−∆t) is drawn from a Gaussian distribution with mean and variance given by, e.g., (Kelly et al. 2009): E(X(t)|X(t−∆t)) = e−∆t/τX(t−∆t) + bτ(1− e−∆t/τ ) Var(X(t)|X(t−∆t)) = τσ 2 2 [1− e−2∆t/τ ] We add a Gaussian deviate normalized by…”
• IS QUASAR OPTICAL VARIABILITY A DAMPED RANDOM WALK? (2012, methodology): “Kelly et al. (2009), Koz lowski et al. (2010) and MacLeod et al. (2010) have shown that the DRW model provides a viable explanation for the variability of individual quasars found in a heterogeneous sample, OGLE (Optical Gravitational Lensing Experiment, Udalski et al. 1997) and SDSS Stripe 82…”
• STELLAR VELOCITY DISPERSION MEASUREMENTS IN HIGH-LUMINOSITY QUASAR HOSTS AND IMPLICATIONS FOR THE AGN BLACK HOLE MASS SCALE (2013, methodology): “The continuum is modeled as an autoregressive process using a damped random walk (DRW) model, which has shown to be a good statistical model of quasar variability (Gaskell & Peterson 1987; Kelly et al. 2009; Koz lowski et al. 2010; MacLeod et al. 2010; Zu et al. 2013).”
• AN ALTERNATIVE APPROACH TO MEASURING REVERBERATION LAGS IN ACTIVE GALACTIC NUCLEI (2010, methodology): “Koz lowski et al. (2010) show how the Kelly et al. (2009) approach can be derived from the SPEAR approach and demonstrated that forecasting is less statistically optimal for parameter estimation than using the complete light curve modeling method of SPEAR, and then applied the process model and the…”
• QUANTIFYING QUASAR VARIABILITY AS PART OF A GENERAL APPROACH TO CLASSIFYING CONTINUOUSLY VARYING SOURCES (2009, methodology): “We have verified the suggestion by Kelly et al. (2009) that quasar light curves are well modeled by the damped random walk process.”
• REVERBERATION MEASUREMENTS OF THE INNER RADIUS OF THE DUST TORUS IN 17 SEYFERT GALAXIES (2014, methodology): “…model for flux variation of the 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…”
• CONSTRAINTS ON BLACK HOLE GROWTH, QUASAR LIFETIMES, AND EDDINGTON RATIO DISTRIBUTIONS FROM THE SDSS BROAD-LINE QUASAR BLACK HOLE MASS FUNCTION (2010, methodology): “Kelly et al. (2009a) found that quasar optical light curves on timescales 7 yr in the rest frame of the quasar are well described by a Gaussian process on the logarithmic scale (see also Kozłowski et al. 2010), with characteristic timescale consistent with accretion disk thermal timescales.”
• PS16dtm: A Tidal Disruption Event in a Narrow-line Seyfert 1 Galaxy (2017, background): “…been known to display variability in the continuum and emission lines (Peterson 2001, and references therein), generally thought to be due to changes in the accretion rate possibly related to disk instabilities or thermal fluctuations (Kawaguchi et al. 1998; Pereyra et al. 2006; Kelly et al. 2009).”
• REVERBERATION MAPPING RESULTS FOR FIVE SEYFERT 1 GALAXIES (2012, background): “…can be modeled as an autoregressive process (Gaskell & Peterson 1987) and a DRW model has been demonstrated to be a good statistical model of quasar variability using large (∼ 104) samples of quasar light curves (e.g., Kelly et al. 2009; Koz lowski et al. 2010; MacLeod et al. 2010; Zu et al. 2012).”