A meta-analysis of core-collapse supernova 56Ni masses

Context. A fundamental property determining the transient behaviour of core-collapse supernovae (CC SNe) is the amount of radioactive Ni-56 synthesised in the explosion. Using established methods, this is a relatively easy parameter to extract from observations. Aims. I provide a meta-analysis of all published Ni-56 masses for CC SNe. Methods. Collating a total of 258 literature Ni-56 masses, I compared distributions of the main CC SN types: SNe II, SNe IIb, SNe Ib, SNe Ic, and SNe IcBL. Results. Using these published values, I calculated a median Ni-56 mass of 0.032 M-circle dot for SNe II (N = 115), 0.102 M-circle dot for SNe IIb (N = 27), 0.163 M-circle dot for SNe Ib (N = 33), 0.155 M-circle dot for SNe Ic (N = 48), and 0.369 M-circle dot for SNe IcBL (N = 32). On average, stripped-enevelope SNe (SE-SNe: IIb, Ib, Ic, and Ic-BL) have much higher values than SNe II. These observed distributions are compared to those predicted from neutrino-driven explosion models. While the SN II distribution follows model predictions, the SE-SNe have a significant fraction of events with Ni-56 masses much higher than predicted. Conclusions. If the majority of published Ni-56 masses are to be believed, these results imply significant differences in the progenitor structures and/or explosion properties between SNe II and SE-SNe. However, such distinct progenitor and explosion properties are not currently favoured in the literature. Alternatively, the popular methods used to estimate Ni-56 masses for SE-SNe may not be accurate. Possible issues with these methods are discussed, as are the implications of true Ni-56 mass differences on progenitor properties of different CC SNe.