Modeling Kilonova Light Curves: Dependence on Nuclear Inputs

Abstract

The mergers of binary neutron stars, as well as black hole–neutron star systems, are expected to produce an electromagnetic counterpart that can be analyzed to infer the element synthesis that occurred in these events. We investigate one source of uncertainties pertinent to lanthanide-rich outflows: the nuclear inputs to rapid neutron capture nucleosynthesis calculations. We begin by examining 32 different combinations of nuclear inputs: eight mass models, two types of spontaneous fission rates, and two types of fission daughter product distributions. We find that such nuclear physics uncertainties typically generate at least one order of magnitude uncertainty in key quantities such as the nuclear heating (one and a half orders of magnitude at 1 day post-merger), the bolometric luminosity (one order of magnitude at 5 days post-merger), and the inferred mass of material from the bolometric luminosity (factor of 8 when considering the 8–10 day region). Since particular nuclear processes are critical for determining the electromagnetic signal, we provide tables of key nuclei undergoing β-decay, α-decay, and spontaneous fission important for heating at different times, identifying decays that are common among the many nuclear input combinations.

Coalescence of black hole–neutron star binaries

“…35 generated by Roberts et al (2017), which shows the abundance pattern of the nucleosynthesis for selected models of black hole-neutron star binaries. The abundance pattern is robust against variation of binary parameters, although the detailed features depend on nuclear physics inputs (see, e.g., Mendoza-Temis et al 2015;Mumpower et al 2016;Wu et al 2016;Zhu et al 2021).…”

The Impact of Nuclear Physics Uncertainties on Interpreting Kilonova Light Curves

“…As can be seen in Figure 7 in [5], the final abundances from the selected simulations differ in the abundance of r-process elements by two to three orders of magnitude. Relevant to the opacity calculations used in kilonova light curve simulations, the mass fraction of lanthanides and actinides at one day after merger differs from 10 −2 to more than 10 −1 as shown in subbarplot of Figure 1.…”

“…The grey lines shows the light curves with the rest of ejecta mass grid for each simulations. This figure is made from same calculations as in figure 8 and 12 from [5].…”

“…We consider lanthanide-rich outflows to emphasize contributions from species with A ≥ 120 in the light curve, following setup and treatments from [5]. These lanthanide-rich outflows will be useful for elucidating neutron-rich ejecta from the mergers of binary neutron stars, as well as black hole-neutron star systems.…”

“…Current simulations could fit optical counterpart to GW170817 qualitatively well; meanwhile, quantitative differences in simulations could be by orders of magnitude (see discussion in [1]). In order to accurately interpret kilonova emission and understand the evolution of rprocess elements in the Universe, recent studies has attempted to explore the complexity from astrophysics [2][3][4], nuclear physics [5][6][7] and atomic physics [8].…”