Mean (black solid line) and rms (red solid line) profile for the Paβ line of all spectra despite the April 2002 spectrum (which had to be excluded here due to its lower spectral resolution). Along with this a model of a symmetrical BEL was plotted which we develop in Sect. 4 (red and black dotted lines) based on Stern et al. (2015). The gray dashed line shows the median flux error of individual pixels at the Paβ line.