How Can the Optical Variation Properties of Active Galactic Nuclei Be Unbiasedly Measured?

Hu, Xu-Fan; Cai, Zhen-Yi; Wang, Jun-Xian

doi:10.3847/1538-4357/ad072f

Cited by 7 publications

(8 citation statements)

References 40 publications

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“…As we mentioned in Section 1, the requirement for recovering the intrinsic damping timescale is that the intrinsic damping timescale (rather than the best-fitting one) should be <10% (or 20%) of the baseline. The results of Hu et al (2024) show that if the intrinsic τ DRW is 10% of the baseline, although the statistical expectation of the output best-fitting τ DRW is the same as the intrinsic τ DRW , its 1σ dispersion is as large as 50%. If one only requires that the best-fitting τ DRW is <10% (or 20%) of the baseline, the statistical expectation of τ DRW can still be significantly biased.…”

Section: Simulation Stepsmentioning

confidence: 98%

“…We then investigate the dependence of the best-fitting τ DRW on wavelength obtained from the CHAR model and compare them with the results in S22. Previous studies have shown that the best-fitting τ DRW is significantly underestimated if the baseline is not longer than 10 (or five) times the intrinsic damping timescale (Kozłowski 2017;Suberlak et al 2021;Hu et al 2024). S22 selects a subsample with the best-fitting damping timescales <20% of the baseline containing 27 sources.…”

Section: Dependence Of τ Drw On Wavelengthmentioning

confidence: 99%

“…If the baseline is not longer than 10 (or five) times the intrinsic damping timescale, τ DRW,disk will be strongly underestimated (e.g., Kozłowski 2017;Suberlak et al 2021;Hu et al 2024). Under such circumstances, the fitted τ DRW,disk should increase with the baseline.…”

Section: Simulation Stepsmentioning

confidence: 99%

“…Recently, Kozłowski (2021) stressed that the baseline should be at least 30 times the intrinsic damping timescale. Hu et al (2024) further suggested that the deviation from the best-fitting damping timescale to the intrinsic value also depends upon the statistical assumptions, including the priors for the DRW parameters and the estimators of the bestfitting damping timescale. In observational studies, it is often argued that if the best-fitting damping timescale is <10% (or 20%) of the baseline, the best-fitting damping timescale is unbiased (e.g., Burke et al 2021;Suberlak et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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How Long Will the Quasar UV/Optical Flickering Be Damped?

Zhou,

Sun,

Cai

et al. 2024

ApJ

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The UV/optical light curves of Active Galactic Nuclei (AGNs) are commonly described by the Damped Random Walk (DRW) model. However, the physical interpretation of the damping timescale, a key parameter in the DRW model, remains unclear. Particularly, recent observations indicate a weak dependence of the damping timescale upon both wavelength and accretion rate, clearly being inconsistent with the accretion-disk theory. In this study, we investigate the damping timescale in the framework of the Corona Heated Accretion disk Reprocessing (CHAR) model, a physical model that describes AGN variability. We find that while the CHAR model can reproduce the observed power spectral densities of the 20 yr light curves for 190 sources from Stone et al., the observed damping timescale, as well as its weak dependence on wavelength, can also be well recovered through fitting the mock light curves with DRW. We further demonstrate that such weak dependence is artificial due to the effect of inadequate durations of light curves, which leads to best-fitting damping timescales lower than the intrinsic ones. After eliminating this effect, the CHAR model indeed yields a strong dependence of the intrinsic damping timescale on the bolometric luminosity and rest-frame wavelength. Our results highlight the demand for sufficiently long light curves in AGN variability studies and important applications of the CHAR model in such studies.

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Section: Simulation Stepsmentioning

confidence: 98%

Section: Dependence Of τ Drw On Wavelengthmentioning

confidence: 99%

Section: Simulation Stepsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

How Long Will the Quasar UV/Optical Flickering Be Damped?

Zhou,

Sun,

Cai

et al. 2024

ApJ

Self Cite

View full text Add to dashboard Cite

show abstract

“…It is often speculated that the damping timescale is closely related to quasar properties (e.g., Kelly et al 2009;Sun et al 2018b). For instance, Burke et al (2021) obtain the relationship between the DRW damping timescale and SMBH mass: Meanwhile, it is stressed that the damping timescale can easily be biased unless the intrinsic t damping is less than 10% of the light-curve duration (e.g., Kozłowski 2017;Hu et al 2024). The synthetic V-band light curve of our target has a long duration of ∼6230 days (observed frame), enabling us to robustly measure the damping timescale since the expected damping timescale in the observed frame is only 109 (1 + z) = 143.7 days (Equation (4); Burke et al 2021).…”

Section: The Damping Timescalementioning

confidence: 99%

A Reverberation Mapping Study of a Highly Variable Active Galactic Nucleus 6dFGS gJ022550.0-060145

Li,

Sun,

Wang

et al. 2024

ApJ

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We use LCOGT observations (MJD 59434−59600) with a total exposure time of ≃50 hr and a median cadence of 0.5 day to measure the interband time delays (with respect to u) in the g, r, and i continua of a highly variable active galactic nucleus (AGN), 6dFGS gJ022550.0-060145. We also calculate the expected time delays of the X-ray reprocessing of a static Shakura–Sunyaev disk according to the source's luminosity and virial black hole mass; the two parameters are measured from the optical spectrum of our spectroscopic observation via the Lijiang 2.4 m telescope. It is found that the ratio of the measured time delays to the predicted ones is 2.6 − 1.3 + 1.3 . With optical light curves (MJD 53650–59880) from our new LCOGT and archival Zwicky Transient Facility, Pan-STARRS, Catalina Sky Survey, and ATLAS observations, and Wide-field Infrared Survey Explorer (WISE) data (MJD 55214−59055), we also measured time delays between WISE W1/W2 and the optical emission. W1 and W2 have time delays (with respect to V), 9.6 − 1.6 + 2.9 × 10 2 days and 1.18 − 0.10 + 0.13 × 10 3 days in the rest frame, respectively; hence, the dusty torus of 6dFGS gJ022550.0-060145 should be compact. The time delays of the W1 and W2 bands are higher than the dusty torus size–luminosity relationship of Lyu et al. By comparing the infrared and optical variability amplitude, we find that the dust-covering factors of the W1 and W2 emission regions are 0.7 and 0.6, respectively. Future broad emission-line reverberation mapping of this target and the results of this work enable us to determine the sizes of the AGN main components simultaneously.

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Is quasar variability regulated by the close environment of accretion?

Wu,

Wang,

Ren

et al. 2024

Monthly Notices of the Royal Astronomical Society

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UV/optical variability in quasars is a well-observed phenomenon, yet its primeval origins remain unclear. This study investigates whether the accretion disk turbulence, which is responsible for UV/optical variability, is influenced by the close environment of the accretion by analyzing the correlation between variability and infrared emission for two luminous SDSS quasar samples. The first sample includes light curves from SDSS, Pan-STARRS, and ZTF g band photometry, while the second sample utilizes SDSS Stripe 82 g band light curves. We explore the correlation between the g band excess variance (σrms) and the wavelength-dependent infrared covering factor (LIR(λ)/Lbol), controlling for the effects of redshift, luminosity, and black hole mass. An anti-correlation between two variables is observed in both samples, which is strongest at wavelengths of 2-3$\hbox{$\mu $m}$ but gradually weakens towards longer wavelength. This suggests the equatorial dusty torus (which dominates near-infrared emission) plays a significant role in influencing the UV/optical variability, while the cooler polar dust (which contributes significantly to mid-infrared emission) does not. The findings indicate that quasar variability may be connected to the physical conditions within the dusty torus which feeds the accretion, and support the notion that the close environment of the accretion plays an important role in regulating the accretion disk turbulence.

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How Can the Optical Variation Properties of Active Galactic Nuclei Be Unbiasedly Measured?

Cited by 7 publications

References 40 publications

How Long Will the Quasar UV/Optical Flickering Be Damped?

How Long Will the Quasar UV/Optical Flickering Be Damped?

A Reverberation Mapping Study of a Highly Variable Active Galactic Nucleus 6dFGS gJ022550.0-060145

Is quasar variability regulated by the close environment of accretion?

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