Temporal evolution of the UV ratio, . The values for SN 2011iv between 0 d and +29 d are shown asred filled circles. For comparison, we calculated the for SN 1980N and SN 1986G (Foley et al. 2008), SN 1992A (Kirshner et al. 1993), SN 2009ig (Foley et al. 2012a), and for SN 2011fe and SN 2013dy (Pan et al. 2015). Results are shown as solidorange, purple, yellow, and dark-blue symbols, respectively. Additionally, the derived from Foley et al. (2008) for SN 1986G, SN 1980N, and SN 1992A are presented as open symbols consisting of the same colour and shape. The small differences arise from different assumptions about redshift and host-galaxy reddening, as describedin Appendix A.