Top panel: peak absolute magnitude () as a function of distance modulus (μ) of the 42 SNe in the sample, shown with the randomly generated SNe IIn (empty red diamonds) introduced to compensate for Malmquist bias. The limiting magnitude m = 21 typical for PTF/iPTF under favourable conditions is shown as a diagonal, dashed line. Vertical and horizontal dashed lines show and μ intervals described in Sect. 4.6. Bottom panel: histograms of the observed and bias-compensated luminosity distributions of the SNe IIn at peak brightness. Bias compensation follows Richardson et al. (2014) and Taddia et al. (2019). K-corrections are not taken into account in the results plotted here, but are studied in Sect. 4.6.