Population Synthesis Study on the Binary Origin of Type Ibn Supernovae

Abstract Type Ibn supernovae (SNe) are a class of SN explosions whose progenitors are surrounded by dense helium-rich circumstellar matter (CSM). Some models have been proposed for how to form the dense CSM, with promising scenarios involving either binaries with a low-mass (≲ 3 M⊙) helium (He) star, or mergers following common envelope phases between a He star and a compact object. Using rapid binary population synthesis calculations, we estimate the event rate of these channels and compare it with the observed SN Ibn rate. We find that exploding low-mass He stars in close binaries (of separations ≲ a few 100 R⊙) can be sufficiently produced to account for the observed event rate of SN Ibn, while the merger scenario can likely account for only a fraction of these SNe. We discuss the types of companions expected in the low-mass He star scenario, finding massive main sequence stars (10–20 M⊙) to be typical, with a potentially non-negligible fraction (<10%) of binaries with white dwarf (WD) companions that have long delay times of up to 100 Myrs.