Example of a simulated binary spectrum and comparison with the double peaked single SMBH spectra obtained assuming a DRW continuum at t_obs = 0. The spectra derived from the light curves in Fig. C.1 with A = 0 (no spiral arms) are shown in blue (σ_DRW = 0.08) and orange (σ_DRW = 0.12), while the resulting simulated binary spectrum is plotted in green. To construct the latter, the individual SMBH spectra were shifted to the blue and red by 10 Å each respectively. Additionally, the spectra obtained with the parameters listed in Tab. C.2 assuming a single SMBH and a DRW continuum are also plotted to show the resemblance with the binary BEL.