English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Several active galactic nuclei show correlated variations in theultraviolet/optical range, with time delays increasing at longer wavelengths.Thermal reprocessing of the X-rays illuminating the accretion disk has beenproposed as a viable explanation. In this scenario, the variable X-ray fluxirradiating the accretion disk is partially reflected in X-rays, and partiallyabsorbed, thermalized and re-emitted with some delay by the accretion disk atlonger wavelengths. We investigate this scenario assuming an X-ray point-likesource illuminating a standard Novikov-Thorne accretion disk, around a rotatingblack hole. We consider all special and general relativistic effects todetermine the incident X-ray flux on the disk and in propagating light from thesource to the disk and to the observer. We also compute the disk reflectionflux taking into consideration the disk ionization. We investigate thedependence of the disk response function and time lags on various physicalparameters, such as black hole mass and spin, X-ray corona height, luminosity,and photon index, accretion rate, inclination, and inner/outer disk radii. Wefound it is important to consider relativistic effects and the disk ionizationin estimating the disk response. We also found a strong non-linearity betweenthe X-ray luminosity and the disk response. We present an analytic function forthe time-lags dependence on wavelength, which can be used to fit observedtime-lag spectra. We also estimate the fraction of the reverberation signalwith respect to the total flux and we suggest possible explanation for the lackof X-ray-ultraviolet/optical correlated variations in a few sources.

UV/optical disk thermal reverberation in AGN: an in-depth study with an analytic prescription for the time-lag spectra