Reverberation mapping of active galactic nuclei: From X-ray corona to dusty torus

Cackett, E.; Bentz, Misty C.; Kara, Erin

doi:10.1016/j.isci.2021.102557

Cited by 127 publications

(91 citation statements)

References 220 publications

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“…More specifically, a high L/L edd corresponds to a small X-ray corona and a large/strong disk, therefore, less reprocessing of X-ray photons occurs in the disk-leading to a smaller variability amplitude; on the other hand, a low L/L edd indicates a large X-ray corona relative to the disk, thus, more reprocessing of X-ray photons occurs at the disk and a larger variability amplitude can be expected. However, recent work on intensive multi-band AGN reverberation mapping for a handful of objects have cast doubt on direct X-ray illumination being the main driver for the UV/optical variability of AGN (Edelson et al 2017;Starkey et al 2017;Edelson et al 2019;Cackett et al 2020), see Cackett et al (2021) for more discussion on this topic.…”

Section: Long-term Amplitude Of Overdamped Dhosmentioning

confidence: 99%

Examining AGN UV/optical Variability Beyond the Simple Damped Random Walk

Yu,

Richards,

Vogeley

et al. 2022

Preprint

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We present damped harmonic oscillator (DHO) light-curve modeling for a sample of 12,714 spectroscopically confirmed quasars in the Sloan Digital Sky Survey Stripe 82 region. DHO is a second-order continuous-time autoregressive moving-average (CARMA) process, and features four independent parameters: a natural oscillation frequency (ω 0 ), a damping ratio (ξ), a characteristic perturbation timescale (τ perturb ), and an amplitude for the perturbing white noise (σ ). The asymptotic variability amplitude of a DHO process is quantified by σ DHO -a function of ω 0 , ξ, τ perturb , and σ . We found that both τ perturb and σ follow different dependencies with rest-frame wavelength (λ RF ) on either side of 2500 Å, whereas σ DHO follows a single power-law relation with λ RF . After correcting for wavelength dependence, σ DHO exhibits anti-correlations with both the Eddington ratio and black hole mass, and τ perturb -with a typical value of days in rest-frame-shows an anti-correlation with the bolometric luminosity. Modeling AGN variability as a DHO offers more insight into how accretion disks work close to the supermassive black holes (SMBHs) at the center of AGN. The newly discovered short-term variability (τ perturb ) and its correlation with bolometric luminosity pave the way for new algorithms that will derive fundamental properties (e.g., Eddington ratio) of AGN using photometric data alone.

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Section: Long-term Amplitude Of Overdamped Dhosmentioning

confidence: 99%

Examining AGN UV/optical Variability Beyond the Simple Damped Random Walk

Yu,

Richards,

Vogeley

et al. 2022

Preprint

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“…In recent years, higher cadence observing campaigns at shorter wavelengths have allowed for reverberation mapping of the continuum-emitting accretion disk in the UV/optical (e.g., Edelson et al 2015;Cackett et al 2018), and even within the inner tens of gravitational radii with X-ray reverberation (e.g., Uttley et al 2014). For a recent review of reverberation mapping from the dusty torus down to the inner accretion disk and corona, see Cackett et al (2021).…”

Section: Introductionmentioning

confidence: 99%

AGN STORM 2. I. First results: A Change in the Weather of Mrk 817

Kara

Mehdipour

Kriss

et al. 2021

ApJ

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We present the first results from the ongoing, intensive, multiwavelength monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this active galactic nucleus was, in part, selected for its historically unobscured nature, we discovered that the X-ray spectrum is highly absorbed, and there are new blueshifted, broad, and narrow UV absorption lines, which suggest that a dust-free, ionized obscurer located at the inner broad-line region partially covers the central source. Despite the obscuration, we measure UV and optical continuum reverberation lags consistent with a centrally illuminated Shakura–Sunyaev thin accretion disk, and measure reverberation lags associated with the optical broad-line region, as expected. However, in the first 55 days of the campaign, when the obscuration was becoming most extreme, we observe a de-coupling of the UV continuum and the UV broad emission-line variability. The correlation recovered in the next 42 days of the campaign, as Mrk 817 entered a less obscured state. The short C iv and Lyα lags suggest that the accretion disk extends beyond the UV broad-line region.

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“…Echo mapping or reverberation mapping (e.g. Blandford & McKee 1982;Peterson 1993;Cackett et al 2021), is a technique that exploits this variability as well as the finite travel time of light to dissect the accretion flow, providing a probe of the structure on a scale equivalent to sub-microarcsecond resolution. This technique is based ★ E-mail: frd3@st-andrews.ac.uk upon variable X-ray/EUV emission originating close to the BH, that propagates outward at the speed of light and is reprocessed, either as thermal continuum emission from the disc or as broad emission lines from the BLR.…”

Section: Introductionmentioning

confidence: 99%

Bayesian analysis of quasar light curves with a running optimal average: new time delay measurements of COSMOGRAIL gravitationally lensed quasars

Donnan

Horne

Santisteban

2021

Monthly Notices of the Royal Astronomical Society

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We present a new method of modelling time-series data based on the running optimal average (ROA). By identifying the effective number of parameters for the ROA model, in terms of the shape and width of its window function and the times and accuracies of the data, we enable a Bayesian analysis, optimising the ROA width, along with other model parameters, by minimising the Bayesian Information Criterion (BIC) and sampling joint posterior parameter distributions using MCMC methods. For analysis of quasar lightcurves, our implementation of ROA modelling can measure time delays among lightcurves at different wavelengths or from different images of a lensed quasar and, in future work, be used to inter-calibrate lightcurve data from different telescopes and estimate the shape and thus the power-density spectrum of the lightcurve. Our noise model implements a robust treatment of outliers and error-bar adjustments to account for additional variance or poorly-quantified uncertainties. Tests with simulated data validate the parameter uncertainty estimates. We compare ROA delay measurements with results from cross-correlation and from JAVELIN, which models lightcurves with a prior on the power-density spectrum. We analyse published COSMOGRAIL lightcurves of multi-lensed quasar lightcurves and present the resulting measurements of the inter-image time delays and detection of microlensing effects.

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Reverberation mapping of active galactic nuclei: From X-ray corona to dusty torus

Cited by 127 publications

References 220 publications

Examining AGN UV/optical Variability Beyond the Simple Damped Random Walk

Examining AGN UV/optical Variability Beyond the Simple Damped Random Walk

AGN STORM 2. I. First results: A Change in the Weather of Mrk 817

Bayesian analysis of quasar light curves with a running optimal average: new time delay measurements of COSMOGRAIL gravitationally lensed quasars

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