2024/11/20 by Hongzhe Zhou, Dong Lai, Zhou, Hongzhe +1
Engineering · Physics and Astronomy · #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Ionosphere and magnetosphere dynamics #Optical Polarization and Ellipsometry #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2411.12953
openalex publication_date 2024/11/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The physical origin of the recently identified slow-moving temperature fluctuations in accretion disks around super-massive black holes (SMBHs) cannot be accounted for by reverberation models. In this work, we propose that large-scale dynamos (LSDs) operating in accretion disks could generate quasi-periodic perturbations in the turbulence viscosity, thereby producing outward-going temperature fluctuations with speeds comparable to those inferred from observations. Furthermore, we find that the UV/optical fluxes of our model are compatible with a damped-random-walk (DRW) process, with a damping time τd consistent with observations. The scaling relation between τd and the rest-frame wavelength λ has a bended shape, τd∝λ at short wavelengths and transitioning to a plateau at long wavelengths. At λ=2500\textÅ, the damping time roughly follows ∝ MBH1/2 when MBH\gtrsim 106M_\odot, consistent with observational constraints, though it tends to be underestimated for lower SMBH masses. Including additional refinements, such as the dependence of dynamo properties on MBH and AGN luminosity, and accounting for X-ray reprocessing, would further enhance the accuracy of the model. In addition, we show that generic disk models with spatially uncorrelated fluctuations cannot explain the observed DRW damping times; spatially correlated fluctuations, such as those discussed in this paper, may be an essential ingredient.