Signatures of 56 Ni Mixing and Neutron-rich Ejecta in Supernovae

Supernova lightcurves are often interpreted with one-zone radioactive-decay models that ignore a key variable that can affect interpretation and inferred parameters: the distribution of radioactive material. Using a multi-shell model, we explore the impact of 56 Ni mixing in supernovae and r-process material in collapsars. Moving 56 Ni outward reduces the overlying diffusion column, producing faster and brighter rises at fixed M Ni, M ej, and E k, and changes the tail through local gamma-ray leakage. A fast, bright rise is not, by itself, evidence for low ejecta mass or a requirement for engine power, with significant overlap between highly mixed and engine-powered lightcurves. One-zone fits to mixed bolometric light curves produce visually good fits but biased parameters. At fixed opacity, outward mixing is absorbed mainly by low inferred M ej and high inferred f Ni, while M Ni remains stable. If opacity is free, the fully mixed case is recovered with kappa fit/kappa input 0.24. These shifts affect inferred explosion energies and progenitor mappings, and amplified in photometric fits. Exploring collapsar r-process enrichment, we find that the signature is not always a NIR excess and depends sensitively on the nickel-powered background, radial placement, angular distribution, and viewing angle of neutron-rich ejecta. In our setup, spherical models often show optical suppression and delayed colour evolution. Our disk-wind models suggest that fast-rising on-axis GRB-SNe are poor r-process targets for equatorially confined neutron-rich winds, and become constraining only if the r-process material reaches latitudes 30 from the equatorial plane.