comparison, the light curves of the archetypal low-luminosity SN 2005cs [@brown09b; @pastorello09] are also plotted by scaling them in magnitude to match it with the observed plateau of . In the early plateau phase, a rapid drop in the UV flux and a slowly declining or constant optical and NIR flux are clearly apparent. The $uvm2$ magnitude declined from about 14.7 to 18.7 mag within 12 days. The decline rates of the flux in UVOT, $U$, $B$, and $V$ bands are almost identical with that of SN 2005cs. Starting from the $uvw2$ until the $R$ band, the measured decline rates from shock breakout to the plateau phase are approximately 0.32, 0.34, 0.25, 0.13, 0.04, 0.01 and 0.01 mag d$^{-1}$. The $IJH$ light curves are almost flat even at early phases of the plateau. For this SN, the plateau is well sampled in the $BVRI$ bands, so we can accurately determine the plateau duration. As discussed in §\[res:rise\], the secondary peak ($t_{p} \sim +5.3$ d) in the prompt light curve is generated by the gradually cooling shock heated SN atmosphere and after that the plateau mechanism starts to dominate. On the other hand, between the plateau and the nebular phase there 