A physical model for the UV/optical power spectra of AGN

Abstract

The UV/optical variability of AGN has long been thought to be driven by the X-ray illumination of the accretion disk. However, recent multi-wavelength campaigns of nearby Seyfert galaxies seem to challenge this paradigm, with an apparent discrepancy between observations and the underlying theory. In order to further probe the connection between the UV/optical and X-ray variability in AGN we developed a physical model to reproduce the UV/optical power spectra (PSDs) of AGN assuming the thermal reprocessing of the X-rays in the disk. This model offers a novel way to probe the innermost regions of AGN. We use our model to study the variability of NGC 5548 and we infer that the X-ray and UV/optical PSDs as well as the interband UV/optical time lags are all well reproduced. We also derive constraints on the source physical parameters, such as the X-ray corona height and the accretion rate. Our results suggest that X-ray disk reprocessing accounts for the full variability properties of this AGN, within the considered time scales. Using earlier data of NGC 5548, we also show that our model can reproduce its PSD in different epochs, establishing the feasibility of using PSD modelling to investigate the time evolution of a source.

15 (+11 in Appendix) pages, 12 figures, accepted for publication by ApJ

References in corpus (14)

• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• The AGN Black Hole Mass Database
• Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548
• 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
• Modeling the UV/optical continuum time-lags in AGN
• UV/optical disk thermal reverberation in AGN: an in-depth study with an analytic prescription for the time-lag spectra
• Discovery of a ~5 day characteristic timescale in the Kepler power spectrum of Zw 229-15
• Iron K and Compton hump reverberation in SWIFT J2127.4+5654 and NGC 1365 revealed by NuSTAR and XMM-Newton
• Observations of MCG-5-23-16 with Suzaku, XMM-Newton and NuSTAR: Disk tomography and Compton hump reverberation
• A hard look at thermal reverberation and optical/UV lags in NGC 5548
• Theoretical modelling of the AGN iron-line vs continuum time-lags in the lamp-post geometry
• A combined timing/spectral study of IRAS 13224-3809 using XMM-Newton data
• Multi-timescale reverberation mapping of Mrk 335
• Multiwavelength power-spectrum analysis of NGC 5548

Cited by in corpus (12)

• Revisiting UV/optical continuum time lags in AGN
• Continuum optical-UV and X-ray variability of AGN: current results and future challenges
• Connecting the X-ray/UV variability of Fairall 9 with NICER: A Possible Warm Corona
• Unusual Hard X-ray Flares Caught in NICER Monitoring of the Binary Supermassive Black Hole Candidate AT2019cuk/Tick Tock/SDSS J1430+2303
• Coronal height constraint in IRAS 13224-3809 and 1H 0707-495 by the random forest regressor
• The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in the last 9 Gyr
• X-ray reverberation modelling of the continuum, optical/UV time-lags in quasars
• 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
• A possible two-fold scenario for the disc-corona of the luminous AGN 1H 0419--577: a high-density disc or a warm corona
• The X-ray/UV Connection in NGC 5548: A Rapidly Varying Corona
• The ensemble broad-frequency power spectrum of Stripe-82 quasars from multiple surveys