Constraining inputs to realistic kilonova simulations through comparison to observed $r$-process abundances

TL;DR

This study compares kilonova simulation inputs to observed solar system r-process abundances, constraining ejecta compositions and ratios to better match observed kilonova light curves and elemental abundances.

Contribution

It introduces a method to constrain kilonova ejecta compositions by comparing simulation inputs to solar r-process abundances, improving model accuracy.

Findings

A specific dynamical ejecta composition with neutron-rich conditions best matches observations.

The wind-to-dynamical mass ratio of 0.47 yields optimal light curve and abundance agreement.

Results highlight the importance of composition assumptions in kilonova modeling.

Abstract

Kilonovae, one source of electromagnetic emission associated with neutron star mergers, are powered by the decay of radioactive isotopes in the neutron-rich merger ejecta. Models for kilonova emission consistent with the electromagnetic counterpart to GW170817 predict characteristic abundance patterns, determined by the relative balance of different types of material in the outflow. Assuming the observed source is prototypical, this inferred abundance pattern in turn must match $r$-process abundances deduced by other means, such as what is observed in the solar system. We report on analysis comparing the input mass-weighted elemental compositions adopted in our radiative transfer simulations to the mass fractions of elements in the Sun, as a practical prototype for the potentially universal abundance signature from neutron-star mergers. We characterize the extent to which our parameter inference results depend on our assumed composition for the dynamical and wind ejecta and examine how the new results compare to previous work. We find that a dynamical ejecta composition calculated using the FRDM2012 nuclear mass and FRLDM fission models with extremely neutron-rich ejecta ($Y_{\rm{e}} = 0.035$) along with moderately neutron-rich ($Y_{\rm e} = 0.27$) wind ejecta composition yields a wind-to-dynamical mass ratio of $M_{\rm{w}}/M_{\rm{d}}$ = 0.47 which best matches the observed AT2017gfo kilonova light curves while also producing the best-matching abundance of neutron-capture elements in the solar system.