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

Abstract

AbstractWe report preliminary results on the analysis of the continuum and Hβ light curves of the type‐1 active galactic nucleus (AGN) NGC 5548. We notice a clear signature of shallowing in the trend between the Hβ and the continuum luminosities. We attempt the recovery of this observed Hβ 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 Hβ 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 Hβ 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 Hβ reverberation mapping estimates. We further discuss the implications of the BLR covering factor and their sizes on recovering the observed trend.