Stochastic Modeling Handbook for Optical AGN Variability

Moreno, Jackeline; Vogeley, Michael S.; Richards, Gordon T.; Yu, Weixiang

doi:10.1088/1538-3873/ab1597

Cited by 60 publications

(53 citation statements)

References 64 publications

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“…We can thus expect at least two breaks in the PSD when convolved with a kernel function with steepened spectral indices as the frequency increases. We note that the same shape is given by a CARMA (2,1) model, which is the next higher order autoregressive model to the DRW (Kasliwal et al 2017;Moreno et al 2019). The light curve from the convolved process should also show a higher correlation coefficient than that of the original temporal flux variation and the correlation should have a duration roughly corresponding to the typical timescale of the kernel.…”

Section: Variability Asymmetry In Quasar Light Curvesmentioning

confidence: 66%

Deep Modeling of Quasar Variability

Tachibana

Graham

Kawai

et al. 2020

ApJ

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Quasars have long been known as intrinsically variable sources, but the physical mechanism underlying the temporal optical/UV variability is still not well understood. We propose a novel nonparametric method for modeling and forecasting the optical variability of quasars utilizing an AE neural network to gain insight into the underlying processes. The AE is trained with ∼15,000 decade-long quasar light curves obtained by the Catalina Real-time Transient Survey selected with negligible flux contamination from the host galaxy. The AE's performance in forecasting the temporal flux variation of quasars is superior to that of the damped random walk process. We find a temporal asymmetry in the optical variability and a novel relation-the amplitude of the variability asymmetry decreases as luminosity and/or black hole mass increases-is suggested with the help of autoencoded features. The characteristics of the variability asymmetry are in agreement with those from the selforganized disk instability model, which predicts that the magnitude of the variability asymmetry decreases as the ratio of the diffusion mass to inflow mass in the accretion disk increases.

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Section: Variability Asymmetry In Quasar Light Curvesmentioning

confidence: 66%

Deep Modeling of Quasar Variability

Tachibana

Graham

Kawai

et al. 2020

ApJ

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“…In addition to a DRW model, we have also considered the CAR(2,1) (Kelly et al 2014) model, i.e., a damped harmonic oscillator, which is often used to describe a periodic signal (Graham et al 2015;Moreno et al 2019). The quality factor Q, defined as the ratio of the detected frequency to the corresponding frequency width, is used as a measure of the significance level.…”

Section: Simulated Light Curvesmentioning

confidence: 99%

Discovery of a Candidate Binary Supermassive Black Hole in a Periodic Quasar from Circumbinary Accretion Variability

Liao

Chen

Liu

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Binary supermassive black holes (BSBHs) are expected to be a generic byproduct from hierarchical galaxy formation. The final coalescence of BSBHs is thought to be the loudest gravitational wave (GW) siren, yet no confirmed BSBH is known in the GW-dominated regime. While periodic quasars have been proposed as BSBH candidates, the physical origin of the periodicity has been largely uncertain. Here we report discovery of a periodicity (P=1607±7 days) at 99.95% significance (with a global p-value of ∼10−3 accounting for the look elsewhere effect) in the optical light curves of a redshift 1.53 quasar, SDSS J025214.67−002813.7. Combining archival Sloan Digital Sky Survey data with new, sensitive imaging from the Dark Energy Survey, the total ∼20-yr time baseline spans ∼4.6 cycles of the observed 4.4-yr (restframe 1.7-yr) periodicity. The light curves are best fit by a bursty model predicted by hydrodynamic simulations of circumbinary accretion disks. The periodicity is likely caused by accretion rate modulation by a milli-parsec BSBH emitting GWs, dynamically coupled to the circumbinary accretion disk. A bursty hydrodynamic variability model is statistically preferred over a smooth, sinusoidal model expected from relativistic Doppler boost, a kinematic effect proposed for PG1302−102. Furthermore, the frequency dependence of the variability amplitudes disfavors Doppler boost, lending independent support to the circumbinary accretion variability hypothesis. Given our detection rate of one BSBH candidate from circumbinary accretion variability out of 625 quasars, it suggests that future large, sensitive synoptic surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time may be able to detect hundreds to thousands of candidate BSBHs from circumbinary accretion with direct implications for Laser Interferometer Space Antenna.

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“…This gives 393 events, of which 209 produced a ZTF alert (the remaining 182 were < 5σ detections above background and therefore did not produce alerts). AGN variability is commonly described statistically as a damped random walk (DRW) process [40,41]. If the flare is consistent with this, then the same parameterized DRW model (within the confidence limits on the model parameters) should describe the time series with and without the flare [42].…”

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confidence: 99%

Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational-Wave Event S190521g

Graham¹,

Ford²,

McKernan³

et al. 2020

Phys. Rev. Lett.

362

340

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We report the first plausible optical electromagnetic counterpart to a (candidate) binary black hole merger. Detected by the Zwicky Transient Facility, the electromagnetic flare is consistent with expectations for a kicked binary black hole merger in the accretion disk of an active galactic nucleus [B. McKernan, K. E. S. Ford, I. Bartos et al., Astrophys. J. Lett. 884, L50 (2019)] and is unlikely [< Oð0.01%Þ)] due to intrinsic variability of this source. The lack of color evolution implies that it is not a supernova and instead is strongly suggestive of a constant temperature shock. Other false-positive events, such as microlensing or a tidal disruption event, are ruled out or constrained to be < Oð0.1%Þ. If the flare is associated with S190521g, we find plausible values of total mass M BBH ∼ 100 M ⊙ , kick velocity v k ∼ 200 km s −1 at θ ∼ 60°in a disk with aspect ratio H=a ∼ 0.01 (i.e., disk height H at radius a) and gas density ρ ∼ 10 −10 g cm −3. The merger could have occurred at a disk migration trap (a ∼ 700r g ; r g ≡ GM SMBH =c 2 , where M SMBH is the mass of the active galactic nucleus supermassive black hole). The combination of parameters implies a significant spin for at least one of the black holes in S190521g. The timing of our spectroscopy prevents useful constraints on broad-line asymmetry due to an off-center flare. We predict a repeat flare in this source due to a reencountering with the disk in ∼1.6 yrðM SMBH =10 8 M ⊙ Þða=10 3 r g Þ 3=2 .

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Stochastic Modeling Handbook for Optical AGN Variability

Cited by 60 publications

References 64 publications

Deep Modeling of Quasar Variability

Deep Modeling of Quasar Variability

Discovery of a Candidate Binary Supermassive Black Hole in a Periodic Quasar from Circumbinary Accretion Variability

Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational-Wave Event S190521g

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