Binary Neutron Star Mergers: Mass Ejection, Electromagnetic Counterparts, and Nucleosynthesis

Abstract

We present a systematic numerical relativity study of the mass ejection and the associated electromagnetic transients and nucleosynthesis from binary neutron star (NS) mergers. We find that a few 10−3 M ⊙ of material is ejected dynamically during the mergers. The amount and the properties of these outflows depend on binary parameters and on the NS equation of state (EOS). A small fraction of these ejecta, typically ∼10−6 M ⊙, is accelerated by shocks formed shortly after merger to velocities larger than 0.6c and produces bright radio flares on timescales of weeks, months, or years after merger. Their observation could constrain the strength with which the NSs bounce after merger and, consequently, the EOS of matter at extreme densities. The dynamical ejecta robustly produce second and third r-process peak nuclei with relative isotopic abundances close to solar. The production of light r-process elements is instead sensitive to the binary mass ratio and the neutrino radiation treatment. Accretion disks of up to ∼0.2 M ⊙ are formed after merger, depending on the lifetime of the remnant. In most cases, neutrino- and viscously driven winds from these disks dominate the overall outflow. Finally, we generate synthetic kilonova light curves and find that kilonovae depend on the merger outcome and could be used to constrain the NS EOS.

Thunder and Lightning: Using Neutron-star Mergers as Simultaneous Standard Candles and Sirens to Measure Cosmological Parameters

“…Using the ejecta masses from Dietrich & Ujevic (2017) and Coughlin et al (2019b), yields similar results, albeit less biased to large H 0 since the predicted ejecta masses are larger. If the ejecta masses from Radice et al (2018) are arbitrarily increased by a factor of 3, the inference on H 0 becomes consistent with those in the existing literature. It is also worth noting that these results would change if the high-spin analysis of the LVC were used instead.…”

“…As such, careful accounting of modeling uncertainties must be done to recover unbiased H 0 estimates. For KNe for example, ejecta properties can vary from study to study (Radice et al 2018), so H 0 estimates may have large systematic errors. Additionally, selection effects must be addressed when the GW detector horizon distances extend to distances at which cosmology can affect the joint GW-EM detection prospects.…”

A multidimensional implementation of the Advanced Spectral neutrino Leakage scheme

“…We examine the modified scheme in typical supernova and neutron star merger remnant snapshots. We focus on the modelling of the absorption in the semi-transparent regime, which is responsible for the neutrino-driven winds (Perego et al 2014;Radice et al 2018b), one of the major ejection channels related to the observed blue EM component. We rely on a spectral treatment of the neutrino-matter interactions, a key ingredient for capturing the composition of the polar ejecta (Foucart et al 2016).…”

LOFAR 144-MHz follow-up observations of GW170817

“…Not only will such measurements provide us with a better understanding of the afterglow, but will also help constrain the neutron star equation of state if the afterglow of the dynamical ejecta is detected (e.g. Radice et al 2018a).…”