Signatures of R-process Enrichment in Supernovae from Collapsars

TL;DR

This paper investigates how r-process element enrichment in collapsar supernovae affects their observable emission, proposing methods to identify such events through early optical and infrared observations to better understand their role in cosmic nucleosynthesis.

Contribution

It presents the first systematic semi-analytical modeling of r-process enriched collapsar supernova emission and strategies for observational detection.

Findings

R-process enrichment can produce a detectable near-infrared excess within ~75 days.

Early optical and NIR monitoring can identify r-process collapsar candidates.

The study outlines optimal observing strategies for future telescopic follow-up.

Abstract

Despite recent progress, the astrophysical channels responsible for rapid neutron capture (r-process) nucleosynthesis remain an unsettled question. Observations of kilonovae following gravitational wave-detected neutron star mergers established mergers as one site of the r-process, but additional sources may be needed to fully explain r-process enrichment in the Universe. One intriguing possibility is that rapidly rotating massive stars undergoing core collapse launch r-process-rich outflows off the accretion disks formed from their infalling matter. In this scenario, r-process winds comprise one component of the supernova (SN) ejecta produced by "collapsar" explosions. We present the first systematic study of the effects of r-process enrichment on the emission from collapsar-generated SNe. We semi-analytically model r-process SN emission from explosion out to late times, and determine its distinguishing features. The ease with which r-process SNe can be identified depends on how effectively wind material mixes into the initially r-process-free outer layers of the ejecta. In many cases, enrichment produces a near infrared (NIR) excess that can be detected within ~75 days of explosion. We also discuss optimal targets and observing strategies for testing the r-process collapsar theory, and find that frequent monitoring of optical and NIR emission from high-velocity SNe in the first few months after explosion offers a reasonable chance of success while respecting finite observing resources. Such early identification of r-process collapsar candidates also lays the foundation for nebular-phase spectroscopic follow-up in the near- and mid-infrared, for example with the James Webb Space Telescope.