Taming the derivative: diagnostics of the continuum and H$\beta$
  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 modelling 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 the rising AGN continuum. With our modelling,
we are able to provide 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.
