Unveiling Accretion-disk Reverberation beneath Broad-line Region Contamination with TILDE

Abstract We present a Bayesian framework, Two-stage Inference for Light curve DEcomposition ( TILDE ), for mapping the accretion disk and the broad-line region (BLR) from active galactic nucleus (AGN) multiband light curves. By inferring delayed BLR contamination from the underlying disk variability, TILDE provides the delay measurements of the disk as well as the BLR. We validate TILDE using synthetic data, finding that TILDE recovers the known time delays of the disk and BLR. By applying TILDE to the Seoul National University AGN Monitoring Project sample, we find that the inferred BLR light curves match the observed H β emission light curves, providing consistent BLR lags compared to the reported H β lags. Using the lag spectrum, effectively corrected for the BLR contamination, we find that the disk size is broadly consistent with the standard thin-disk model, suggesting that BLR contamination can significantly bias the disk size derived from the cross-correlation analysis of the broadband photometry. These results demonstrate that the new inference method is a powerful tool for determining both disk and BLR sizes from broadband photometry in the era of time-domain surveys.