Pulsational Pair-instability Supernovae in Very Close Binaries

Pair-instability and pulsational pair-instability supernovae (PPISNe) have not been unambiguously observed so far. They are, however, promising candidates for the progenitors of the heaviest binary black hole (BBH) mergers detected. If these BBHs are the product of binary evolution, then PPISNe could occur in very close binaries. Motivated by this, we discuss the implications of a PPISN happening with a close binary companion and what impact these events have on the formation of merging BBHs through binary evolution. For this, we have computed a set of models of metal-poor (Z(circle dot)/10) single helium stars using the MESA software instrument. For PPISN progenitors with pre-pulse masses >50 M-circle dot we find that, after a pulse, heat deposited throughout the layers of the star that remain bound causes it to expand to more than 100 R-circle dot for periods of 10(2)-10(4) yr depending on the mass of the progenitor. This results in long-lived phases of Roche lobe overflow or even common-envelope events if there is a close binary companion, leading to additional electromagnetic transients associated with PPISN eruptions. If we ignore the effect of these interactions, we find that mass loss from PPISNe reduces the final BH spin by similar to 30%, induces eccentricities below the threshold of detectability of the LISA observatory, and can produce a double-peaked distribution of measured chirp masses in BBH mergers observed by ground-based detectors.