Temperature Profiles of Accretion Disks in Luminous Active Galactic Nuclei derived from Ultraviolet Spectroscopic Variability

Abstract

The characteristic timescale ($\tau$) of continuum variability of the accretion disk in active galactic nuclei (AGNs) is known to be related to the thermal timescale, which is predicted to scale with AGN luminosity ($L$) and restframe wavelength (${\lambda }_{\mathrm{RF}}$) as $t_{\mathrm{th}}\propto L^{0.5}{\lambda }_{\mathrm{RF}}^2$ in the standard disk model. Using multi-epoch spectroscopic data from the Sloan Digital Sky Survey Reverberation Mapping project, we construct ultraviolet ensemble structure functions of luminous AGNs as a function of their luminosity and wavelength. Assuming that AGNs exhibit a single universal structure function when $\Delta t$ is normalized by $\tau$, wherein $\tau \propto L^a{\lambda }_{\mathrm{RF}}^b$, we find $a=0.50\pm 0.03$ and $b=1.42\pm 0.09$. While the value of $a$ aligns with the prediction from the standard disk model, $b$ is significantly smaller than expected, suggesting that the radial temperature (color) profile of the accretion disk is significantly steeper (shallower) than the standard disk model. Notably, this discrepancy with theory has been observed in previous studies based on spectroscopic reverberation mapping and gravitational microlensing. Although no current model of accretion disks fully matches our results, our findings provide valuable constraints for testing future physical models.

8 pages, 3 figures; accepted for publication in Astronomy & Astrophysics

References in corpus (29)

• A Catalog of Quasar Properties from SDSS DR7
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• Sizes and Temperature Profiles of Quasar Accretion Disks from Chromatic Microlensing
• The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• A characteristic optical variability timescale in astrophysical accretion disks
• The Spatial Structure of An Accretion Disk
• Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 = the Einstein Cross. II. Energy profile of the accretion disk
• The Sloan Digital Sky Survey Reverberation Mapping Project: No Evidence for Evolution in the M-sigma Relation to z~1
• Optical variability of AGN in the PTF/iPTF survey
• Self-shadowing Effects of Slim Accretion Disks in Active Galactic Nuclei: Diverse Appearance of the Broad-line Region
• The Sloan Digital Sky Survey Stripe 82 Imaging Data: Depth-Optimized Co-adds Over 300 Deg^2 in Five Filters
• Limitations on the recovery of the true AGN variability parameters using Damped Random Walk modeling
• Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548
• Supermassive black holes with high accretion rates in active galactic nuclei. XI. Accretion disk reverberation mapping of Mrk 142
• Detection of Time Lags Between Quasar Continuum Emission Bands based on Pan-STARRS Light-curves
• Optical Variability of Quasars with 20-Year Photometric Light Curves
• A Study of Gravitational Lens Chromaticity using Ground-based Narrow Band Photometry
• AGN Continuum Reverberation Mapping Based on Zwicky Transient Facility Light Curves
• Chandra Survey of Nearby Galaxies: A Significant Population of Candidate Central Black Holes in Late-type Galaxies
• Near Infrared Variability of obscured and unobscured X-ray selected AGN in the COSMOS field
• How far is quasar UV/optical variability from damped random walk at low frequency?
• A hard look at thermal reverberation and optical/UV lags in NGC 5548
• Quasar Microlensing Variability Studies Favor Shallow Accretion Disk Temperature Profiles
• Rimmed and Rippled Accretion Disc Models to Explain AGN Continuum Lags
• Universality in the Random Walk Structure Function of Luminous Quasi-Stellar Objects
• Ensemble power spectral density of SDSS quasars in UV/optical bands
• Black Hole Mass Estimation in Type 1 AGN: H$\beta$ vs. Mg II lines and the role of Balmer continuum
• Spectral shape corrections for SDSS BOSS quasars

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