Shock Cooling Emission from Late-time Mass Loss in Low-mass He Star Binaries

Abstract A subset of hydrogen-poor supernovae (SNe) exhibit signatures of interaction with nearby dense circumstellar material (CSM). These SNe may originate from interacting binary systems, in which the SN progenitor experiences intense mass loss when it overflows its Roche lobe close to core collapse. In this work, we explore the appearance of SNe from low-mass stripped-star progenitors in binary systems for a range of initial orbital periods and masses. We model the CSM based on the stripped stars’ mass-loss history in binary stellar evolution simulations, then numerically explode the progenitors to calculate the SN light curves. Shock cooling emission (SCE) from the CSM dominates the early light curves, followed by SCE from the extended helium envelopes of the stripped stars, which form helium recombination plateaus. The appearance and properties of our model light curves are reflected in a subset of Type Ib/n SNe from the literature. Some of our models tend to evolve rapidly and are quite hot during SCE, so they may naturally explain some fraction of fast blue optical transients (FBOTs). Since the mass-loss history of our binary progenitor models can produce dense CSM out to ∼10 18 cm, interaction of this CSM with the SN shock could generate bright late-time radio emission in the years after the optical SN. Searching for late-time rising radio emission from FBOTs could be used to test which events are explained by the scenario we explore here.