2023ApJ...948L..23W

Spectroscopic reverberation mapping (RM) is a direct approach widely used to determine the mass of black holes (BHs) in active galactic nuclei (AGNs). However, it is very time consuming and difficult to apply to a large AGN sample. The empirical relation between the broad-line region size and luminosity (HβR_BLR-L) provides a practical alternative yet is subject to large scatter and systematic bias. Based on the relation between the continuum emitting region size and luminosity (R_CER-L) reported by Netzer (2022), we present a new BH mass estimator via continuum RM (CRM) by comparing R_CER and R_BLR, assuming that the continuum lags are dominated by the diffuse continuum emission. Using a sample of 21 AGNs, we find a tight R_BLR-R_CER relation (scatter∼0.28 dex) and that R_BLR is larger than R_CER at 5100 Å by an average factor of 8.1. This tight relation enables the BH mass estimation based on the CRM combined with the velocity information. Applying the relation to rest objects in our CRM sample, we demonstrate that the predicted R_BLR,CRM follows the existing HβR_BLR-L relation well and the estimated CRM BH masses are consistent with the RM/single-epoch BH masses using Hβ. This method will provide significant applications for BH mass estimation thanks to the short continuum lags and the easily accessible high-cadence, large-area photometric data, especially in the era of Legacy Survey of Space and Time.