The impact of isomers on a kilonova associated with neutron star mergers

Abstract

We investigate the significance of isomers on a kilonova associated with neutron star mergers (NSMs) for the first time. We calculate the evolution of abundances and energy generation rates (${\dot{\epsilon }}_{\mathrm{nuc}}$) of ejecta from NSMs, taking into account ${\beta }^{-}$ decay through isomers. We find that for ejecta with electron fraction ($Y_e$) of $0.2-0.3$, ${\dot{\epsilon }}_{\mathrm{nuc}}$ is appreciably changed from those without isomers, due to the large change in timing of ${\beta }^{-}$ decay through the isomeric states of ${}^{123,125,127}\mathrm{Sn}$ and ${}^{128}\mathrm{Sb}$. In particular, the effects of the isomers on ${\dot{\epsilon }}_{\mathrm{nuc}}$ are prominent for ejecta of $Y_e\sim 0.25$, which could emit a fraction of an early, blue component of a kilonova observed in GW170817. When the excitation from a ground state to its isomeric state is important, the isomers of ${}^{129}\mathrm{Sb}$ and ${}^{129,131}\mathrm{Te}$ also cause additional and appreciable change in ${\dot{\epsilon }}_{\mathrm{nuc}}$. Furthermore, we demonstrate that larger amounts of lanthanide-free ejecta result in a better fit of an observed light curve of the kilonova in GW170817 if the isomers are taken into account.

6 pages, 4 figures. Accepted for publication in MNRAS

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Cited by in corpus (13)

• Kilonovae across the nuclear physics landscape: The impact of nuclear physics uncertainties on r-process-powered emission
• Modeling Kilonova Light Curves: Dependence on Nuclear Inputs
• Atlas of Nuclear Isomers -- Second Edition
• Astromers: Nuclear Isomers in Astrophysics
• Astromers in the radioactive decay of r-process nuclei
• Isochronic evolution and the radioactive decay of r-process nuclei
• High-precision measurements of low-lying isomeric states in ${}^{120-124}$In with JYFLTRAP double Penning trap
• Alpha decay law of excited nuclei and its role in stellar decay rates
• Neutron transfer reactions on the ground state and isomeric state of a 130Sn beam
• How Do Nuclear Isomers Influence the Gamma-Ray Bursts in Binary Neutron Star Mergers?
• Gamma-ray emission from decays of boosted nuclei in protomagnetar jets
• Sensitivity of Neutron-Rich Nuclear Isomer Behavior to Uncertainties in Direct Transitions
• Exploration for Astromers near ${}^{132}$Sn with the Canadian Penning Trap