Taming the derivative: Diagnostics of the continuum and Hβ emission in a prototypical Population B active galaxy

We report preliminary results on the analysis of the continuum and H beta light curves of the type-1 active galactic nucleus (AGN) NGC 5548. We notice a clear signature of shallowing in the trend between the H beta and the continuum luminosities. We attempt the recovery of this observed H beta emission trend as a response to large continuum flux increase using CLOUDY photoionization simulations. We explore a wide range in the physical parameters space for modeling the H beta emission from the broad-line region (BLR) appropriate for this source. We employ a constant density, single-cloud model approach in this study and successfully recover the observed shallowing of the H beta emission with respect to rising AGN continuum. With our modeling, we are able to provide the constraints on the local BLR cloud density and recover the BLR distances (from the continuum source) consistent with the H beta reverberation mapping estimates. We further discuss the implications of the BLR covering factor and their sizes on recovering the observed trend.

Automated summary

This study reports preliminary results on analyzing the continuum and H beta light curves of the type-1 AGN NGC 5548. A clear signature of shallowing in the trend between the H beta and the continuum luminosities is observed, and it is successfully recovered using CLOUDY photoionization simulations. The study provides constraints on the BLR cloud density and recovers the BLR distances consistent with the H beta reverberation mapping estimates.