2025MNRAS.541.3748K

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 ($\lesssim 3~\mathrm{ M}_\odot$) 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 $\lesssim$ a few 100 $\mathrm{ R}_\odot$) 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-$20\, \mathrm{ M}_\odot$) to be typical, with a potentially non-negligible fraction ($< 10~{{\ \rm per\ cent}}$) of binaries with white dwarf (WD) companions that have long delay times of up to 100 Myrs.