Late-time post-merger modeling of a compact binary: effects of relativity, r-process heating, and treatment of transport effects

Studying Postmerger Outflows from Magnetized-neutrino-cooled Accretion Disks

“…Here we measured the averaged electron fraction around 0.1 < Y e < 0.3, which is consistent with the GRMHD model in Fernandez et al (2019), and it is relatively lower than the averaged value reported by Haddadi et al (2022;0.3 < Y e < 0.39) for viscous disks. Our results also show that outflow mass increases sharply at early times, matching well with the GRMHD models, while the viscous disks have this large growth at a much later time in Fernandez et al (2019).…”

“…Therefore, more advanced neutrino treatments such as leakage or neutrino radiation transport schemes along with composition evolution are needed to provide better accuracy. Our equation of state does not include nuclei heavier than helium; however, Haddadi et al (2022) and showed that the inclusion of these nuclei in the equation of state may cause significant changes in the outflow's mass and velocity. In addition, the numerical scheme and grid resolution typically have impacts on the modeling of the kilonova emission.…”

“…One crucial thermal component in studying outflows is the inclusion of the r-process heating and neutrino cooling terms in the long-term hydro simulations (see the discussion and Equations ( 20)-( 21) from Foucart et al 2021). A recent study by Haddadi et al (2022) for long-term 2D viscous disk simulations indicated that adding these terms to hydro equations after 1 s evolution increases the outflow mass by 30%. Another important physics to be considered for kilonova studies is a neutrino's flavor oscillations.…”

“…In the literature, a smaller extraction radius ∼200-500 km has been used to measure the dynamical ejecta or the ejecta from magnetized postmerger HMNSs with tracers (see, e.g., Combi &Siegel 2023 andde Haas et al 2022), and each tracer has to satisfy the geodesic or Bernoulli condition to identify the unbound mass. However, the disk wind is a different scenario; the recent studies by Haddadi et al (2022) showed that if the r-process heating source terms are included in the evolution of the postmerger ejecta during a multisecond simulation, the ejecta's velocity needs to be measured at a much larger distance. This study claimed that the ejecta is being continuously accelerated as a result of the r-process heating and reaches its asymptotic value around r ∼ 40,000 km.…”