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 ≳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.

Keywords

• R-process
• Core-collapse supernovae
• Nucleosynthesis
• Transient detection