The Nickel Mass Distribution of Stripped-envelope Supernovae: Implications for Additional Power Sources

We perform a systematic study of the 56Ni mass (MNi) 27 stripped-envelope supernovae (SESNe) by modeling their light-curve tails, highlighting that use "Arnett's rule" overestimates MNi for SESNe factor ?2. Recently, Khatami & Kasen presented new model relating peak time (tp) and luminosity (Lp) radioactively powered supernova to its addresses several limitations Arnett-like models, but depends on dimensionless parameter, ?. Using observed tp, Lp, tail-measured values SESNe, we observationally calibrate ? first time. Despite scatter, demonstrate with empirically calibrated provides significantly improved measurements when only photospheric data are available. However, these constrained systematically lower than those inferred from numerical simulations, primarily because sample has higher (0.2–0.4 dex) Lp given MNi. While effects due composition, mixing, asymmetry can increase none explain low values. discrepancy be alleviated if ?7%–50% comes sources other radioactive decay. Either shock cooling or magnetar spin-down could provide requisite luminosity. Finally, find even our measurements, still ?3 larger hydrogen-rich Type II SNe, indicating inherently different in terms initial distributions progenitors explosion mechanisms.