Did Binary Neutron Star Merger GW170817 Leave Behind A Long-lived Neutron Star?

TL;DR

This paper explores how a long-lived neutron star from GW170817 could produce a hidden equatorial outflow that causes late-time re-brightening in the observed light curve, aligning with current observations.

Contribution

It introduces a semi-analytic model for a beamed equatorial outflow from a neutron star remnant, explaining late-time re-brightening in GW170817's light curve.

Findings

The model matches observed light curves of GW170817.

Hidden outflows can become visible as re-brightening at late times.

Predictions are made for future afterglow observations.

Abstract

We consider the observational implications of the binary neutron star (BNS) merger GW170817 leaving behind a rapidly rotating massive neutron star that launches a relativistic, equatorial outflow as well as a jet. We show that if the equatorial outflow (ring) is highly beamed in the equatorial plane, its luminosity can be "hidden" from view until late times, even if carrying a significant fraction of the spin-down energy of the merger remnant. This hidden ring reveals itself as a re-brightening in the light curve once it slows down enough for Earth to be within the ring's relativistic beaming solid angle. We compute semi-analytic light curves using this model and find they are in agreement with the observations thus far, and we provide predictions for the ensuing afterglow.