Using AGN lightcurves to map accretion disc temperature fluctuations

Abstract

We introduce a new model for understanding AGN continuum variability. We start from a Shakura--Sunyaev thin accretion disc with a steady-state radial temperature profile $T(R)$ and assume that the variable flux is due to axisymmetric temperature perturbations $\delta T(R,t)$. After linearizing the equations, we fit UV-optical AGN lightcurves to determine $\delta T(R,t)$ for a sample of seven AGNs. We see a diversity of $|\delta T/T|\sim 0.1$ fluctuation patterns which are not dominated by outgoing waves traveling at the speed of light as expected for the "lamppost" model used to interpret disc reverberation mapping studies. Rather, the most common pattern resembles slow ($v\ll c$) ingoing waves. An explanation for our findings is that these ingoing waves trigger central temperature fluctuations that act as a lamppost, producing lower amplitude temperature fluctuations moving outwards at the speed of light. The lightcurves are dominated by the lamppost signal -- even though the temperature fluctuations are dominated by other structures with similar variability time-scales -- because the discs exponentially smooth the contributions from the slower moving ($v\ll c$) fluctuations to the observed lightcurves. This leads to lightcurves that closely resemble the expectations for a lamppost model but with the slow variability time-scales of the ingoing waves. This also implies that longer time-scale variability signals will increasingly diverge from lamppost models because the smoothing of slower-moving waves steadily decreases as their period or spatial wavelength increases.

arXiv comment18 pages, 25 figures. Published by MNRAS. Animated versions of select figures (see Section 8) can be found at https://github.com/jackneustadt/disc-gifs

References in corpus (37)

• LSST: from Science Drivers to Reference Design and Anticipated Data Products
• The Swift Ultra-Violet/Optical Telescope
• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• A Cosmology Calculator for the World Wide Web
• Are the Variations in Quasar Optical Flux Driven by Thermal Fluctuations?
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• On the X-ray time lags in the black hole candidates
• Simultaneous X-ray/optical/UV snapshots of active galactic nuclei from XMM-Newton: spectral energy distributions for the reverberation mapped sample
• Quantifying Quasar Variability As Part of a General Approach To Classifying Continuously Varying Sources
• Is Quasar Optical Variability a Damped Random Walk?
• The flux-dependent amplitude of broadband noise variability in X-ray binaries and active galaxies
• Space Telescope and Optical Reverberation Mapping Project. III. Optical Continuum Emission and Broad-Band Time Delays in NGC 5548
• A Description of Quasar Variability Measured Using Repeated SDSS and POSS Imaging
• Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548
• Testing thermal reprocessing in AGN accretion discs
• Long-term optical variability properties of the Palomar-Green quasars
• Thermal Instability and Photoionized X-ray Reflection in Accretion Disks
• Kepler Observations of Rapid Optical Variability in Active Galactic Nuclei
• Quasar Accretion Disks Are Strongly Inhomogeneous
• The First Swift Intensive AGN Accretion Disk Reverberation Mapping Survey
• Space Telescope and Optical Reverberation Mapping Project. I. Ultraviolet Observations of the Seyfert 1 Galaxy NGC 5548 with the Cosmic Origins Spectrograph on Hubble Space Telescope
• A characteristic optical variability timescale in astrophysical accretion disks
• Global Radiation Magneto-hydrodynamic Simulations of Sub-Eddington Accretion Disks around Supermassive Black Holes
• The Variable Diffuse Continuum Emission of Broad Line Clouds
• Swift monitoring of NGC 4151: Evidence for a Second X-ray/UV Reprocessing
• A Stochastic Model for the Luminosity Fluctuations of Accreting Black Holes
• Variability-Selected Quasars in MACHO Project Magellanic Cloud Fields
• Intensive disc-reverberation mapping of Fairall 9: 1st year of Swift & LCO monitoring
• Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548
• Quantifying the Diffuse Continuum Contribution of BLR Clouds to AGN Continuum Inter-band Delays
• Supermassive black holes with high accretion rates in active galactic nuclei. XI. Accretion disk reverberation mapping of Mrk 142
• Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. VIII. Structure of the Broad-Line Region and Mass of the Central Black Hole in Mrk 142
• On the multi-wavelength variability of Mrk 110: Two components acting at different timescales
• Opacity Driven Convection and Variability in Accretion Disks around Supermassive Black Holes
• The Sloan Digital Sky Survey Reverberation Mapping Project: Accretion and Broad Emission Line Physics from a Hypervariable Quasar
• Modeling the X-ray - UV Correlations in NGC 3516
• Modeling the X-ray - UV Correlations in NGC 7469

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• The UV/optical Continuum Reverberation Mapping of Eight Active Galactic Nuclei with Swift: Further Evidence for the Outer Component
• Untangling the Complex Nature of AGN Variability with Fairall 9
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• The X-ray/UV Connection in NGC 5548: A Rapidly Varying Corona
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