Supernovae in colliding-wind binaries: observational signatures in the first year

Abstract

ABSTRACT When a core-collapse supernova (SN) explodes in a binary star system, the ejecta might encounter an overdense shell, where the stellar winds of the two stars previously collided. In this work, we investigate effects of such interactions on SN light curves on time-scales from the early flash ionization signatures to approximately one year after the explosion. We construct a model of the colliding-wind shell in an orbiting binary star system and we provide an analytical expression for the shell thickness and density, which we calibrate with three-dimensional adaptive mesh refinement hydrodynamical simulations probing different ratios of wind momenta and different regimes of radiative cooling efficiency. We model the angle-dependent interaction of SN ejecta with the circumstellar medium and estimate the shock radiative efficiency with a realistic cooling function. We find that the radiated shock power exceeds typical Type IIP SN luminosity only for double red supergiant binaries with mass ratios q ≳ 0.9, wind mass-loss rates $\dot{M}\gtrsim 10^{-4}\, \rm M_\odot \, \text{yr}^{-1}$, and separations between about 50 and 1500 au. The required $\dot{M}$ increases for binaries with smaller q or primaries with faster wind. We estimate that ≪1 per cent of all collapsing massive stars satisfy the conditions on binary mass ratio and separation. Recombination luminosities due to colliding wind shells are at most a factor of 10 higher than for an otherwise unperturbed constant-velocity wind, but higher densities associated with wind acceleration close to the star provide much stronger signal.