Observability of inflated companion stars after supernovae in massive binaries

We carry out a systematic study of the response of companion stars in massive binaries after being impacted by supernova (SN) ejecta. A total of 720 1D stellar evolution calculations are performed to follow the inflation and contraction of the star in response to the energy injection and how it depends on various parameters. We find that the maximum luminosity achieved during the inflated phase is only dependent on the stellar mass and we derive an analytic formula to describe the relation. There is also a tight correlation between the duration of expansion and the intersected energy. These correlations will be useful to constrain pre-SN binary parameters from future detections of inflated companions. We also discuss the possible outcomes of the binary system when the companion inflation is taken into account. Based on simple binary population synthesis, we estimate that ∼1-3 per cent of stripped-envelope SNe may have observable inflated companions. Finally, we apply our models to the observed companion of SN 2006jc and place strong constraints on the possible pre-SN binary parameters.