The phase is given relative to our estimate of the epoch of explosion on MJD 56 593.42. Limiting magnitudes are to 3σ.

K-corrections were calculated by first using the LSQ13cuw spectroscopy and the snake code (SuperNova Algorithm for K-correction Evaluation) within the S3 package (Inserra et al., in prep.). These values were then interpolated to all epochs of photometric observations. The K-corrections are not included in the photometry, as up to an epoch of about 30 days after explosion the derived K-corrections are smaller or similar to the error in the photometry whereas our analysis focusses primarily on the early epochs. LSQ = La Silla-QUEST; ST = ESO 1.0 m Schmidt Telescope; CRTS = Catalina Real-time Transient Survey; CSSST = Catalina Sky Survey Schmidt telescope; LT = Liverpool Telescope; NTT = New Technology Telescope; LCOGT = Las Cumbres Observatory Global Telescope Network 1 m telescope. We note that the NTT filters are not standard Sloan filters and that CRTS data are unfiltered, see also Sect. 2.1. The transmission curves for the respective filters are available at: LT g′r′i′: http://telescope.livjm.ac.uk/TelInst/Inst/IOO/; LCOGT g′r′i′: http://lcogt.net/configdb/filter/; NTT 641, 782, 784, 705: http://www.eso.org/sci/facilities/lasilla/instruments/efosc/inst/Efosc2Filters.html; LSQ wideband filter: Baltay et al. (2013), Fig. 2.