Temporal evolution (from bottom to top) of the normalized, narrow-line, and host-galaxy-subtracted Hβ profiles in velocity space. A suitable linear pseudo-continuum was subtracted, and the spectra are flux-shifted for clarity. MUSE spectra are shown in blue, SALT spectra are shown in red. The central velocity v = 0 km s⁻¹ is indicated by a dashed line. We give the spectrum ID, the date of observations, and the time in days with respect to the peak time t₀ = 58301.44 MJD of the transient event. The reconstructed Hβ profile for Spectrum 1 (2015 September 24) is shown as a dotted line (see Sect. 3.3).