Possible signatures of ejecta-companion interaction in iPTF 13bvn

We investigate the possible effects of the supernova (SN) ejecta hitting the companion star in iPTF 13bvn, focusing on the observable features when it becomes visible. iPTF 13bvn is a type Ib SN that may become the first case in which its progenitor is identified as a binary (by observations in the near future). According to calculations by Bersten et al. the progenitor should have a mass ≈3.5 M⊙ to reproduce the SN light curve, and such compact stars can only be produced via binary evolution. This is one of the reasons that we expect the progenitor to be a binary, but this should be confirmed by observing the remaining companion after the SN. Bersten et al.s evolutionary calculations suggest that the companion star will be an overluminous OB star at the moment of SN. With a combination of hydrodynamical and evolutionary simulations, we find that the secondary star will be heated by the SN ejecta and expand to have larger luminosities and lower surface effective temperatures. The star will look like a red supergiant and this should be taken into account when searching for the companion star in the SN ejecta in future observations.