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

Abstract

Core-collapse supernovae (SNe) are candidate sites for rapid neutron capture process (r-process) nucleosynthesis. We explore the effects of enrichment from r-process nuclei on the light curves of hydrogen-rich SNe and assess the detectability of these signatures. We modify the radiation hydrodynamics code, SuperNova Explosion Code, to include the approximate effects of opacity and radioactive heating from r-process elements in the supernova (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 hydrogen-rich SNe (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 SNe 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 r-process-rich layers are mixed at least halfway to the ejecta surface. This detectability threshold can roughly be reproduced analytically using a two-zone (kilonova-within-an-SN) picture. Assuming that a small fraction of SNe produce a detectable r-process yield of M r ≳ 10−2 M ⊙, and respecting constraints on the total Galactic production rate, we estimate that ≳103–104 SNe need be observed to find one r-enriched event, a feat that may become possible with the Vera Rubin Observatory.