Our fitting procedure for the optical spectra. The procedure is illustrated for the spectrum taken with the Baade telescope on MJD 59195. (a) Continuum fit. The continuum is fit with a function consisting of a single power law (red dotted), an FeII-emission template (black), and a host-galaxy template (green). The residuals for all fits are shown underneath their respective plots. (b) Fit of continuum-subtracted spectrum around Hβ. The combined fit consists of five Gaussian profiles, two for the narrow [OIII] (black dotted) lines and a narrow (green dashed), broad (blue dot-dashed), and very broad (black dashed) component for Hβ. (c) Fit of continuum-subtracted spectrum around Hα. The combined fit for this region consists of six Gaussians: two for the narrow [NII] lines, two for the narrow [SII] lines (dotted black), and three for the Hα emission, with the same colours as the components used to fit Hβ.