Radiation hydrodynamics modeling of kilonovae with SNEC

Abstract

We develop a method to compute synthetic kilonova light curves that combines numerical relativity simulations of neutron star mergers and the SNEC radiation-hydrodynamics code. We describe our implementation of initial and boundary conditions, rprocess heating, and opacities for kilonova simulations. We validate our approach by carefully checking that energy conservation is satisfied and by comparing the SNEC results with those of two semi-analytic light curve models. We apply our code to the calculation of color light curves for three binaries having different mass ratios (equal and unequal mass) and different merger outcome (short-lived and long-lived remnants). We study the sensitivity of our results to hydrodynamic effects, nuclear physics uncertainties in the heating rates, and duration of the merger simulations. We also study the impact of shocks possibly launched into the outflows by a relativistic jet. None of our models match AT2017gfo, the kilonova in GW170817. This points to possible deficiencies in the merger simulations and to the need to go beyond the assumption of spherical symmetry adopted in this work.

$r$-process Nucleosynthesis and Kilonovae from Hypermassive Neutron Star Remnants

“…SNEC (Morozova et al 2015;Wu et al 2021) is a 1D Lagrangian equilibrium-diffusion radiation hydrodynamics code capable of simulating the hydrodynamical evolution of merger ejecta and the resulting kilonova emission. For kilonova modeling, the nickel heating term relevant for the supernova case in SNEC is replaced by a prescription for radioactive heating due to decay of 𝑟-process nuclei.…”

“…For kilonova modeling, the nickel heating term relevant for the supernova case in SNEC is replaced by a prescription for radioactive heating due to decay of 𝑟-process nuclei. The time-dependent heating rate is derived in Wu et al (2021) based on the nucleosynthesis calculations of Perego et al (2020) by constructing fits over a comprehensive grid of 11700 trajectories, covering a wide range of 𝑌 𝑒 , entropy 𝑠 and expansion timescale 𝜏: At early times 𝑡 0.1 days, fits are constructed using the analytic formula proposed by Korobkin et al (2012). At later times 𝑡 0.1 days, a power-law fit is used.…”

Electromagnetic counterparts of binary neutron star mergers leading to a strongly magnetized long-lived remnant neutron star

“…This hydrodynamical effect in the subsequent evolution could be reflected in the light curve of the EM counterparts. Currently, there are only a limited number of studies that consider the long-term hydrodynamics evolution of ejecta to predict the property of the EM counterparts (Rosswog et al 2014;Grossman et al 2014;Fernández et al 2015Fernández et al , 2017Foucart et al 2021;Kawaguchi et al 2021;Wu et al 2021).…”