Corona-heated Accretion-disk Reprocessing: Frequency-Resolved Lag Predictions for UV/Optical Reverberation Mapping of Active Galactic Nuclei

Abstract

Continuum reverberation mapping with high-cadence, long-term UV/optical monitoring of Active Galactic Nuclei (AGNs) enables us to resolve the AGN central engine sizes on different timescales. The frequency-resolved time lags of NGC 5548 (the target for the AGN STORM I campaign) are inconsistent with the X-ray reprocessing of the classical Shakura $\&$ Sunyaev disk model. Here we show that the frequency-resolved time lags in NGC 5548 can be well produced by the Corona-Heated Accretion-disk Reprocessing (CHAR) model. Moreover, we make the CHAR model predictions of the frequency-resolved time lags for Mrk 817, the source of the AGN STORM II campaign. We also obtain the frequency-resolved time lags as a function of the black-hole mass and Eddington ratio, which is valid for black-hole masses from $10^{6.5}$ to $10^9\ M_{\odot}$, and Eddington ratios from 0.01 to 1. Moreover, we demonstrate that, with the time spans of current continuum reverberation-mapping campaigns, the lag-luminosity relation of the CHAR model can be $\tau_{\mathrm{gz}}\propto L_{\mathrm{5100}}^{0.55\pm0.04}$, which is consistent with observations. Future observations can test our results and shed new light on resolving the AGN central engine.