Early BB temperature evolution of iPTF13bvn (left panel). Early bolometric luminosity calculated using the temperature evolution from the left panel and the Stefan-Boltzmann law (center panel). Early g, r, and i-band flux of iPTF13bvn (right panel). In each panel we also show the relevant quantity predicted by the PN1 models for the cooling emission after shock breakout for progenitor radii of 3, 10, and 15 R_⊙. A model with a radius of 10 R_⊙ is consistent with the observed data. In the left and center panels the 3 R_⊙ and 15 R_⊙ models are shown as thin dashed gray lines and the optimal model with a radius of 10 R_⊙ is a thicker dashed black line. In the right panel the 3 R_⊙ model LCs are displayed as dotted lines and the 15 R_⊙ model LCs are thin dashed lines in matching colors to the photometry. The 10 R_⊙ model LCs are shown as thicker solid lines.