Gravitational Microlensing

Wambsganß, J.

doi:10.1007/978-3-540-30310-7_4

Cited by 106 publications

(33 citation statements)

References 60 publications

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“…Direct probes of the sub-microarcsecond structure of AGNs have been therefore limited to very long baseline interferometry studies of the radio-emitting regions, gravitational microlensing studies of the accretion disk (see review by Wambsganss 2006), and reverberation mapping of the broad-line regions (BLRs; Blandford & McKee 1982;Peterson 1993). The technique of reverberation mapping (a.k.a.…”

Section: Introductionmentioning

confidence: 99%

An Alternative Approach to Measuring Reverberation Lags in Active Galactic Nuclei

Kochanek

Peterson

2011

ApJ

382

543

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Motivated by recent progress in the statistical modeling of quasar variability, we develop a new approach to measuring emission-line reverberation lags to estimate the size of broad-line regions (BLRs) in active galactic nuclei. Assuming that all emission-line light curves are scaled, smoothed, and displaced versions of the continuum, this alternative approach fits the light curves directly using a damped random walk model and aligns them to recover the time lag and its statistical confidence limits. We introduce the mathematical formalism of this approach and demonstrate its ability to cope with some of the problems for traditional methods, such as irregular sampling, correlated errors, and seasonal gaps. We redetermine the lags for 87 emission lines in 31 quasars and reassess the BLR size-luminosity relationship using 60 Hβ lags. We confirm the general results from the traditional crosscorrelation methods, with a few exceptions. Our method, however, also supports a broad range of extensions. In particular, it can simultaneously fit multiple lines and continuum light curves which improves the lag estimate for the lines and provides estimates of the error correlations between them. Determining these correlations is of particular importance for interpreting emission-line velocity-delay maps. We can also include parameters for luminosity-dependent lags or line responses. We use this to detect the scaling of the BLR size with continuum luminosity in NGC 5548.

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Section: Introductionmentioning

confidence: 99%

An Alternative Approach to Measuring Reverberation Lags in Active Galactic Nuclei

Kochanek

Peterson

2011

ApJ

382

543

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“…Sources that are smaller than the Einstein radius of the stars, typically ∼10 16 cm, show time variable fluxes whose amplitude is determined by the source size (see the review by Wambsganss 2006). Smaller sources have larger variability amplitudes than larger sources.…”

Section: Introductionmentioning

confidence: 99%

The Quasar Accretion Disk Size-Black Hole Mass Relation

Morgan

Kochanek

Morgan

et al. 2010

ApJ

350

484

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We use the microlensing variability observed for 11 gravitationally lensed quasars to show that the accretion disk size at a rest-frame wavelength of 2500 Å is related to the black hole mass by log(R 2500 /cm) = (15.78 ± 0.12) + (0.80 ± 0.17) log(M BH /10 9 M ). This scaling is consistent with the expectation from thin-disk theory (R ∝ M 2/3 BH ), but when interpreted in terms of the standard thin-disk model (T ∝ R −3/4 ), it implies that black holes radiate with very low efficiency, log(η) = −1.77 ± 0.29 + log(L/L E ), where η = L/(Ṁc 2 ). Only by making the maximum reasonable shifts in the average inclination, Eddington factors, and black hole masses can we raise the efficiency estimate to be marginally consistent with typical efficiency estimates (η ≈ 10%). With one exception, these sizes are larger by a factor of ∼4 than the size needed to produce the observed 0.8 μm quasar flux by thermal radiation from a thin disk with the same T ∝ R −3/4 temperature profile. While scattering a significant fraction of the disk emission on large scales or including a large fraction of contaminating line emission can reduce the size discrepancy, resolving it also appears to require that accretion disks have flatter temperature/surface brightness profiles.

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“…Gravitational microlensing (Chang & Refsdal 1979, 1984; see also Kochanek 2004 andWambsganss 2006) is the main tool used to estimate both parameters, either from time variability or through the wavelength dependence of the microlensing magnification. Microlensing studies (see e.g., Pooley et al 2007;Morgan et al 2010;Blackburne et al 2011Blackburne et al , 2014Blackburne et al , 2015Sluse et al 2011;Jiménez-Vicente et al 2012Hainline et al 2013;Mosquera et al 2013;MacLeod et al 2015) have found that the mean sizes of quasar accretion disks are roughly a factor of 2-3 greater than the predictions of the standard thin disk model.…”

Section: Introductionmentioning

confidence: 99%

Structure of the Accretion Disk in the Lensed Quasar Q2237+0305 From Multi-Epoch and Multi-Wavelength Narrowband Photometry

Muñoz

Vives-Arias

Mosquera

et al. 2016

ApJ

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We present estimates for the size and the logarithmic slope of the disk temperature profile of the lensed quasar Q2237+0305, independent of the component velocities. These estimates are based on six epochs of multiwavelength narrowband images from the Nordic Optical Telescope. For each pair of lensed images and each photometric band, we determine the microlensing amplitude and chromaticity using pre-existing mid-IR photometry to define the baseline for no microlensing magnification. A statistical comparison of the combined microlensing data (6 epochs×5 narrow bands×6 image pairs) with simulations based on microlensing magnification maps gives Bayesian estimates for the half-light radius oflt-day, and p=0.95±0.33 for the exponent of the logarithmic temperature profile µ -T R p 1 . This size estimate is in good agreement with most recent studies. Other works based on the study of single microlensing events predict smaller sizes, but could be statistically biased by focusing on high-magnification events.

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Gravitational Microlensing

Cited by 106 publications

References 60 publications

An Alternative Approach to Measuring Reverberation Lags in Active Galactic Nuclei

An Alternative Approach to Measuring Reverberation Lags in Active Galactic Nuclei

The Quasar Accretion Disk Size-Black Hole Mass Relation

Structure of the Accretion Disk in the Lensed Quasar Q2237+0305 From Multi-Epoch and Multi-Wavelength Narrowband Photometry

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