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 CHAR model predictions of the frequency-resolved time lags for Mrk 817, the source of the AGN STORM II campaign. We also obtain frequency-resolved time lags as a function of the BH mass and Eddington ratio, which is valid for BH masses from 106.5 to 109 M ⊙ 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 τgz∝L51000.55±0.04 , which is consistent with observations. Future observations can test our results and shed new light on resolving the AGN central engine.