Temperature Fluctuations in Quasar Accretion Discs from Spectroscopic Monitoring Data

Abstract

Neustadt & Kochanek (2022, hereafter NK22) proposed a new method to reconstruct the temperature perturbation map (as functions of time and disc radius) of AGN accretion discs using multi-wavelength photometric light curves. We apply their technique to 100 quasars at $z=0.5-2$ from the Sloan Digital Sky Survey Reverberation Mapping project, using multi-epoch spectroscopy that covers rest-frame UV-optical continuum emission from the quasar and probes days to months timescales. Consistent with NK22 for low-redshift AGNs, we find that the dominant pattern of disc temperature perturbations is either slow inward/outward moving waves with typical amplitudes $\delta T/T_0\sim 10\%$ traveling at $\sim 0.01-0.1c$, with a typical radial frequency of $\sim$ 0.5 dex in $\log R$, or incoherent perturbations. In nearly none of the cases do we find clear evidence for coherent, fast outgoing temperature perturbations at the speed of light, reminiscent of the lamppost model; but such lamppost signals may be present in some quasars for limited periods of the monitoring data. Using simulated data, we demonstrate that high-fidelity temperature perturbation maps can be recovered with high-quality monitoring spectroscopy, with limited impact from seasonal gaps in the data. On the other hand, reasonable temperature perturbation maps can be reconstructed with high-cadence photometric light curves from the Vera C. Rubin Observatory Legacy Survey of Space and Time. Our findings, together with NK22, suggest that internal disc processes are the main driver for temperature fluctuations in AGN accretion discs over days to months timescales.

20 pages, 15 figures. Supplementary data is located at https://zenodo.org/record/7195997 and figures, animations, and python code are located at https://github.com/Zstone19/TempMap

References in corpus (22)

• Array Programming with NumPy
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• Stability of Relativistic Jets from Rotating, Accreting Black Holes via Fully Three-Dimensional Magnetohydrodynamic Simulations
• Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk
• 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
• Quasar Accretion Disks Are Strongly Inhomogeneous
• The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• The Sloan Digital Sky Survey Reverberation Mapping Project: No Evidence for Evolution in the M-sigma Relation to z~1
• Intensive disc-reverberation mapping of Fairall 9: 1st year of Swift & LCO monitoring
• Improving Damped Random Walk parameters for SDSS Stripe 82 Quasars with Pan-STARRS1
• Optical Variability of Quasars with 20-Year Photometric Light Curves
• Examining AGN UV/optical Variability Beyond the Simple Damped Random Walk
• AGN Continuum Reverberation Mapping Based on Zwicky Transient Facility Light Curves
• Correlated X-ray and Optical Variability in Mkn 509
• The Mass of Quasars
• Using AGN lightcurves to map accretion disc temperature fluctuations
• The LSST era of supermassive black holes accretion-disk reverberation mapping
• Optical continuum photometric reverberation mapping of the Seyfert-1 galaxy Mrk509
• Estimating reddening of the continuum and broad-line region of active galactic nuclei: the mean reddening of NGC 5548 and the size of the accretion disc
• Dust and the intrinsic spectral index of quasar variations: hints of finite stress at the innermost stable circular orbit

Cited by in corpus (1)

• Optical Variability Structure Function of Low-Luminosity AGN using ATLAS Lightcurves