Reconciling the quasar microlensing disc size problem with a wind model of active galactic nucleus

Li, Y.; Yuan, Feng; Dai, Xinyu

doi:10.1093/mnras/sty3245

Cited by 22 publications

(32 citation statements)

References 78 publications

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“…This result is further supported by Pan-STARRS observations (Jiang et al 2017), which might, however, suffer from significant selection bias (see Appendix A of Homayouni et al 2019). Possible explanations involve alternative reprocessors, e.g., SSDs with powerful winds which have flatter disk temperature profiles (Li et al 2019;Sun et al 2019), SSDs with non-blackbody disk emission (Hall et al 2018), inhomogeneous SSDs with global temperature fluctuations (Cai et al 2020;Sun et al 2020a), or nondisk UV/optical continuum emission from the more extended broad-line clouds (Cackett et al 2018;Lawther et al 2018;Sun et al 2018a;Chelouche et al 2019;Korista & Goad 2019).…”

supporting

confidence: 62%

“…Alternatively, Sun et al (2019) (also see Li et al 2019) consider SSDs with powerful winds and find that such disks can have larger apparent sizes than the no-wind SSDs. Then, our results indicate that the disk-wind strength should decrease with increasing L, contradicting observations that luminous AGNs generally have stronger disk winds than their faint counterparts (e.g., Laor & Brandt 2002;Ganguly et al 2007).…”

Section: Implications For the X-ray Reprocessing Modelsmentioning

confidence: 99%

“…If we also consider the CHAR model with winds, the predicted median time lag approaches the SSD model and is more consistent with observations. At the same time, the windy CHAR model has a larger half-light radius and can account for the microlensing observations (e.g., Morgan et al 2018;Li et al 2019). In summary, the possible discrepancy between the inter-band time lags and microlensing observations might be a unique probe of winds and corona-disk magnetic coupling.…”

Section: Comparing With Microlensing Observationsmentioning

confidence: 99%

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Faint AGNs Favor Unexpectedly Long Inter-band Time Lags

Li,

Sun,

et al. 2021

Preprint

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Inconsistent conclusions are obtained from recent active galactic nuclei (AGNs) accretion disk inter-band time-lag measurements. While some works show that the measured time lags are significantly larger (by a factor of ∼ 3) than the theoretical predictions of the Shakura & Sunyaev disk (SSD) model, others find that the time-lag measurements are consistent with (or only slightly larger than) that of the SSD model. These conflicting observational results might be symptoms of our poor understanding of AGN accretion physics. Here we show that sources with larger-than-expected time lags tend to be less-luminous AGNs. Such a dependence is unexpected if the inter-band time lags are attributed to the light-travel-time delay of the illuminating variable X-ray photons to the static SSD. If, instead, the measured inter-band lags are related not only to the static SSD but also to the outer broad emission-line regions (BLRs; e.g., the blended broad emission lines and/or diffuse continua), our result indicates that the contribution of the non-disk BLR to the observed UV/optical continuum decreases with increasing luminosity (L), i.e., an anti-correlation resembling the well-known Baldwin effect. Alternatively, we argue that the observed dependence might be a result of coherent disk thermal fluctuations as the relevant thermal timescale, τ TH ∝ L 0.5 . With future accurate measurements of inter-band time lags, the above two scenarios can be distinguished by inspecting the dependence of inter-band time lags upon either the BLR components in the variable spectra or the timescales.

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supporting

confidence: 62%

Section: Implications For the X-ray Reprocessing Modelsmentioning

confidence: 99%

Section: Comparing With Microlensing Observationsmentioning

confidence: 99%

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Faint AGNs Favor Unexpectedly Long Inter-band Time Lags

Li,

Sun,

et al. 2021

Preprint

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“…One possible explanation of the larger disk sizes is nonthermal disk emission caused by a low-density disk atmosphere (Hall et al 2018). Another explanation is a disk wind that leads to a higher effective temperature in the outer part of the accretion disk (e.g., Li et al 2019;Sun et al 2019). Gaskell (2017) found that the internal reddening of AGNs that leads to an underestimation of the far-UV luminosity can be an explanation of the discrepancy as well.…”

Section: Introductionmentioning

confidence: 99%

Quasar Accretion Disk Sizes from Continuum Reverberation Mapping in the DES Standard-star Fields

Martini

Davis

et al. 2020

ApJS

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Measurements of the physical properties of accretion disks in active galactic nuclei are important for better understanding the growth and evolution of supermassive black holes. We present the accretion disk sizes of 22 quasars from continuum reverberation mapping with data from the Dark Energy Survey (DES) standard-star fields and the supernova C fields. We construct continuum light curves with the griz photometry that span five seasons of DES observations. These data sample the time variability of the quasars with a cadence as short as 1 day, which corresponds to a rest-frame cadence that is a factor of a few higher than most previous work. We derive time lags between bands with both JAVELIN and the interpolated cross-correlation function method and fit for accretion disk sizes using the JAVELIN thin-disk model. These new measurements include disks around black holes with masses as small as ∼10 7 M e , which have equivalent sizes at 2500 Å as small as ∼0.1 lt-day in the rest frame. We find that most objects have accretion disk sizes consistent with the prediction of the standard thin-disk model when we take disk variability into account. We have also simulated the expected yield of accretion disk measurements under various observational scenarios for the Large Synoptic Survey Telescope Deep Drilling Fields. We find that the number of disk measurements would increase significantly if the default cadence is changed from 3 days to 2 days or 1 day.

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“…Previous studies have found that γ CSD around accreting BHs is usually in the range of ∼ 0.75 − 1.0 (Frank et al 1992;Yuan & Narayan 2014;Jiang et al 2014). But, an even shallower profile could be attributed to a disk wind (Li et al 2019;Sun et al 2019). To cover a wide range of The blue dashed (red solid) lines correspond to expanding (contracting) BBHs.…”

Section: Methodsmentioning

confidence: 96%

Hot Circumsingle Disks Drive Binary Black Hole Mergers in Active Galactic Nucleus Disks

Li,

Dempsey,

et al. 2021

Preprint

Self Cite

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Binary black hole (BBH) mergers, particularly those with component masses in the pair-instability gap, may be produced by hierarchical mergers in the disks surrounding Active Galactic Nuclei (AGN). While the interaction of an embedded BBH with an AGN disk is typically assumed to facilitate merger, recent high-resolution hydrodynamical simulations challenge this assumption. However, these simulations often have simplified treatments for the gas thermodynamics. In this work, we model the possible consequence of various feedback from an embedded BBH with a simple model that maintains an enhanced temperature profile around each binary component. We show that when the mini-disks around each BH become hotter than the background by a factor of three, the BBH orbital evolution switches from expansion to contraction. By analyzing the gravitational torque profile, we find that this change in direction is driven by a weakening of the mini-disk spirals and their positive torque on the binary. Our results highlight the important role of thermodynamics around BBHs and its effect on their orbital evolution, suggesting that AGN disks could be efficient factories for BBH mergers.

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Reconciling the quasar microlensing disc size problem with a wind model of active galactic nucleus

Cited by 22 publications

References 78 publications

Faint AGNs Favor Unexpectedly Long Inter-band Time Lags

Faint AGNs Favor Unexpectedly Long Inter-band Time Lags

Quasar Accretion Disk Sizes from Continuum Reverberation Mapping in the DES Standard-star Fields

Hot Circumsingle Disks Drive Binary Black Hole Mergers in Active Galactic Nucleus Disks

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