Helium giant stars as progenitors of rapidly fading Type Ibc supernovae

Type I rapidly fading supernovae (RFSNe) appear to originate from hydrogen-free stars with large radii that produce predominantly shock-cooling light curves, in contrast with more typical ^(56)Ni-rich SNe Ibc. However, it remains to be determined what types of stars would produce bright shock-cooling light curves without significant contribution from radioactive nickel. Bare helium stars in the mass range ∼2-4M⊙ are known to hydrostatically develop radii as large as 100 R⊙ or more due to strong He and C shell burning outside of a core with a sharp density gradient. We produce several such stellar models and demonstrate that, when exploded, these helium giants can naturally produce RFSN light curves. Since many prototypical SNe Ibc should come from large-radius stars in this mass range as well, we predict that these RFSNe may be distinct from SNe Ibc solely due to the absence of substantial ^(56)Ni.