Modeling GW170817 based on numerical relativity and its implications

TL;DR

This paper uses numerical relativity simulations to interpret GW170817, suggesting the merger resulted in a long-lived neutron star and highlighting the importance of the neutron-star equation of state in explaining observed electromagnetic counterparts.

Contribution

It provides a detailed interpretation of GW170817 based on numerical relativity, emphasizing the role of a long-lived neutron star and constraints on the neutron-star equation of state.

Findings

GW170817 is consistent with a long-lived hypermassive or supramassive neutron star remnant.

The neutron-star equation of state must be sufficiently stiff, with M_max > 2M_sun.

No detection of a relativistic optical counterpart constrains M_max to approximately 2.15-2.25M_sun.

Abstract

Gravitational-wave observation together with a large number of electromagnetic observations shows that the source of the latest gravitational-wave event, GW170817, detected primarily by advanced LIGO, is the merger of a binary neutron star. We attempt to interpret this observational event based on our results of numerical-relativity simulations performed so far paying particular attention to the optical and infra-red observations. We finally reach a conclusion that this event is described consistently by the presence of a long-lived hypermassive or supramassive neutron star as the merger remnant, because (i) significant contamination by lanthanide elements along our line of sight to this source can be avoided by the strong neutrino irradiation from it and (ii) it could play a crucial role to produce an ejecta component of appreciable mass with fast motion in the post-merger phase. We also point out that (I) the neutron-star equation of state has to be sufficiently stiff (i.e., the maximum mass of cold spherical neutron stars, M_max, has to be appreciably higher than 2M_sun in order that a long-lived massive neutron star can be formed as the merger remnant for the binary systems of GW170817, for which the initial total mass is >~ 2.73M_sun and (II) no detection of relativistic optical counterpart suggests a not-extremely high value of M_max approximately as 2.15-2.25M_sun.