An intrinsic Baldwin effect in the Hβ broad emission line in the spectrum of NGC 5548

We investigate possibility of an intrinsic Baldwin effect (i.e., nonlinear emission-line response to continuum variations) in the broad Hbeta emission line of the active galaxy NGC 5548 using cross-correlation techniques to remove light-travel time effects from the data. We find a nonlinear relationship between the Hbeta emission line and continuum fluxes that is in good agreement with theoretical predictions. We suggest that similar analysis of multiple lines might provide a useful diagnostic of physical conditions in the broad-line region.