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NGC 5548 has been hailed as an archetypical type-1 active galactic nuclei(AGN) and serves as a valuable laboratory to study the long-term variation ofits broad-line region (BLR). In this work, we re-affirm our finding on theconnection between the continuum variability in the optical regime and thecorresponding H$\beta$ response to it, in order to realize the increase, albeitwith a gradual saturation, in the H$\beta$ emitting luminosity with increasingAGN continuum. This effect is also known as the Pronik-Chuvaev effect after theauthors who first demonstrated this effect using long-term monitoring ofanother well-studied Type-1 AGN - Mrk 6. We employ a homogeneous,multi-component spectral fitting procedure over a broad range of spectralepochs that is then used to create the continuum and H$\beta$ light curves. Wefocus on the epoch range 48636-49686 MJD, different from our previous analysis.We again notice a clear signature of shallowing in the trend between theH$\beta$ and the continuum luminosities. We attempt to recover this H$\beta$emission trend as a response to a significant continuum flux increase usingCLOUDY photoionization simulations and employ a suitable broad-band spectralenergy distribution for this source. We explore the wide range in the physicalparameters space for modelling the H$\beta$ emission from the BLR appropriatefor this source. We employ a constant density, single cloud model approach inthis study and successfully recover the observed shallowing of the H$\beta$emission with respect to the rising AGN continuum and provide constraints onthe local BLR densities and the location of the H$\beta$ emitting BLR whichagrees with the H$\beta$ time-lags reported from the long-term reverberationmapping monitoring. On the contrary, we do not find a significant breathingeffect in the location of the H$\beta$ line-emitting BLR for this epoch in NGC5548.

Saturation of the curve -- diagnostics of the continuum and H$\beta$ emission in Population B active galaxy NGC 5548