r-Process and Kilonovae

TL;DR

This paper investigates the radioactive isotopes powering kilonova emissions from neutron star mergers, highlighting the roles of beta-decay, alpha-decay, and fission in shaping the light curve and providing insights into r-process nucleosynthesis.

Contribution

It identifies specific isotopes responsible for early and late kilonova emission phases, linking them to r-process nucleosynthesis beyond stable elements.

Findings

Early emission dominated by 66Ni decay chain

Late emission influenced by alpha-decay and fission of trans-Pb isotopes

Supports r-process nucleosynthesis beyond the heaviest stable elements

Abstract

The kilonova associated with the neutron star merger GW170817 provides us with several hints to elucidate the nature of the r-process in the universe. In this article, we inspect the radioactive isotopes that powered the kilonova emission, provided that the merger ejecta consisted of material with a solar r-like abundance pattern. It is suggested that the early (1-10 days after merger) kilonova emission is mainly due to the beta-decay chain 66Ni -> 66Cu -> 66Zn, which can be the source of the steepening of the light curve at about 7 days. The late time (> 10 days) heaing is attributed to the alpha-decay and fission (254Cf) of trans-Pb species (in addition to beta-decay), which can be the signature of r-processing beyond the heaviest stable elements. This article summarizes a recent work by the author (Wanajo 2018) with the additional calculations of kilonova light curves by using a numerical code in Hotokezaka and Nakar (2019).