  Many core-collapse supernova progenitors are presumed to be in binary
systems. If a star explodes in a binary system, the early supernova light curve
can be brightened by the collision of the supernova ejecta with the companion
star. The early brightening can be observed when the observer is in the
direction of the hole created by the collision. Based on a population synthesis
model, we estimate the fractions of core-collapse supernovae in which the
light-curve brightening by the collision can be observed. We find that 0.19% of
core-collapse supernova light curves can be observed with the collisional
brightening. Type Ibc supernova light curves are more likely to be brightened
by the collision (0.53%) because of the high fraction of the progenitors being
in binary systems and their proximity to the companion stars. Type II and IIb
supernova light curves are less affected (~1e-3% and ~1e-2%, respectively).
Although the early, slow light-curve declines of some Type IIb and Ibc
supernovae are argued to be caused by the collision with the companion star
(e.g. SN 2008D), the small expected fraction, as well as the unrealistically
small separation required, disfavour the argument. The future transient survey
by the Large Synoptic Survey Telescope is expected to detect ~10 Type Ibc
supernovae with the early collisional brightening per year, and they will be
able to provide information on supernova progenitors in binary systems.
