The Effects of r-Process Enrichment in Hydrogen-Rich Supernovae

Core-collapse supernovae are candidate sites for the rapid neutron capture process (r-process). We explore the effects of enrichment from r-process nuclei on the light-curves of hydrogen-rich supernovae (SNe IIP) and assess the detectability of these signatures. We modify the radiation transport code to include the approximate effects of opacity and radioactive heating from r-process elements in the SN ejecta. We present models spanning a range of total r-process masses M_ r and their assumed radial distribution within the ejecta, finding that M_ r≳ 10^-2 M_⊙ is sufficient to induce appreciable differences in their light-curves as compared to ordinary SNe IIP (without any r-process elements). The primary photometric signatures of r-process enrichment include a shortening of the plateau phase, coinciding with the hydrogen-recombination photosphere retreating to the r-process-enriched layers, and a steeper post-plateau decline associated with a reddening of the SN colors. We compare our r-process-enriched models to ordinary IIP models and observational data, showing that yields of M_ r≳ 10^-2 M_⊙ are potentially detectable across several of the metrics used by transient observers, provided that the r-process rich layers are mixed ≳ halfway to the ejecta surface. This detectability threshold can roughly be reproduced analytically using a two-zone ("kilonova within a supernova") picture. Assuming that a small fraction of SNe produce a detectable r-process yield M_ r≳ 10^-2M_⊙, and respecting constraints on the total Galactic production rate, we estimate that ≳ 10^3-10^4 SNe need be observed to find one r-enriched event, a feat that may become possible with the Vera Rubin Observatory.