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

Abstract

We explore the electromagnetic counterparts that will associate with binary neutron star mergers for the case that remnant massive neutron stars survive for 0.5 s after the merger. For this study, we employ the outflow profiles obtained by long-term general-relativistic neutrino-radiation magnetohydrodynamics simulations with a mean field dynamo effect. We show that a synchrotron afterglow with high luminosity can be associated with the merger event if the magnetic fields of the remnant neutron stars are significantly amplified by the dynamo effect. We also perform a radiative transfer calculation for kilonovae and find that for the highly amplified magnetic field cases, the kilonovae can be bright in the early epoch (t ≤ 0.5 d), while it shows rapid declining ( 1 d) emission and long-lasting (∼ 10 d) emission in the optical and near-infrared wavelength, respectively. All these features have not been found in GW170817, indicating that the merger remnant neutron star formed in GW170817 might have collapsed to a black hole within several hundreds ms or magnetic-field amplification might be a minor effect.

Magnetar-powered neutrinos and magnetic moment signatures at IceCube

“…Note the relation n e = Y e n b , where n b = n p + n n is the baryon number density and n p = n e is the proton number density. Here, the benchmark value taken for ρ B aligns with numerical simulations for magnetar born in a merger event [44]. Furthermore, as elaborated in the following, larger values of ρ B would lead to significant attenuation of the neutrino flux.…”

Comprehensive study of mass ejection and nucleosynthesis in binary neutron star mergers leaving short-lived massive neutron stars

“…However, such a radio transient has not been observed in untargeted surveys or follow-up observations of short gamma-ray bursts (Horesh et al 2016). This also indicates that a binary neutron star merger resulting in a long-lived massive neutron star as its remnant may not be a frequent event (Kawaguchi et al 2022).…”

On the diversity of magnetar-driven kilonovae

“…Another source of uncertainty is nuclear physics itself, which has been demonstrated previously to contribute to up to an order of magnitude uncertainty at peak (Zhu et al 2021;Barnes et al 2021). Both these factors, alongside other issues explored by numerical simulations (e.g., Kawaguchi et al 2022;Wu et al 2022), the sig-nificance of neutron precursor emission (Metzger et al 2015a), shock heated ejecta (Gottlieb et al 2018;Piro & Kollmeier 2018), neutrino-driven winds (Metzger et al 2018), interaction with the jet (Klion et al 2021;Nativi et al 2021Nativi et al , 2022, and viewing angle dependencies (Klion et al 2022) indicate systematic uncertainties, which until resolved suggest that the relative brightness of a kilonova alone may not a good diagnostic for distinguishing an engine-driven kilonova from an ordinary one. This is especially true for "Case 2"like systems unless they are observed quite early.…”

“…However, in many cases, the same observations could be interpreted with the afterglow produced by a structured relativistic jet (Beniamini et al 2020;, or attributed to systematics and not require a neutron star central engine (Zhu et al 2021;O'Connor et al 2021). Theoretically, the impact of the long-lived neutron star remnants, in particular on kilonovae, has been explored in detail in many works (e.g., Yu et al 2013;Metzger & Piro 2014;Metzger & Fernández 2014;Siegel & Ciolfi 2016;Li et al 2018;Wollaeger et al 2019;Kawaguchi et al 2020Kawaguchi et al , 2021Kawaguchi et al , 2022Ai et al 2022). However, these works either do not explore the entire parameter space or make different simplifying assumptions in modelling, such as ignoring relativistic dynamics, gamma-ray leakage, pair cascades, the dynamical evolution of the neutron star, or gravitational-wave emission.…”