Temperature and radius evolution of the blackbody component. Black data points are those derived using combined BAT+XRT data (Starling et al. 2011) plus the temperature determinations using GROND data ( ≈ 46 ks). The first data bin from Starling et al. (2011) represents the interval from  − 175 to 144 s, however, due to fitting and plotting purposes, here it corresponds to 0–144 s. Solid, dashed and dotted lines are different power-law models (see main text). Best fits to temperature and radius are shown in grey and brown solid lines, respectively. Grey crosses (upper panel) and open circles (lower panel) are measurements of XRF 060218/SN 2006aj taken from Kaneko et al. (2007) and Campana et al. (2006), respectively.