Black-body temperature (blue dots) and radius evolution (red dots) as inferred from the SED of Swift data. The light blue and red squares show the temperature and radius evolution assuming a blackbody. The SED was corrected by a reddening value of E(B − V) = 0.0154  ±  0.001 mag and with R_V = 3.1. The horizontal line indicates the kT = 1 eV level, where recombination is expected to become relevant afterwards. The vertical black solid line indicates the assumed explosion epoch at MJD 56946.1  ±  3 and the vertical dashed lines is at the assumed offset (Δt₀ = −1.75) in the explosion epoch, for the optimal cooling model from RW11. The red dashed lines shows a power-law fit to the photospheric radii (only using the data points with kT_ph >  1eV) while the blues dashed lines shows the same for the Temperatures. The black curved dashed lines are the fits assuming the RW11 model for T_ph and R_ph.