Does a long-lived remnant neutron star exist after short gamma-ray burst GRB 160821B?

TL;DR

This paper models the afterglow of GRB 160821B and finds evidence suggesting a long-lived neutron star remnant, indicating such remnants may be common in neutron star mergers and informing the neutron star equation of state.

Contribution

It provides the first modeling that supports the existence of a non-thermal pulsar wind nebula in a short gamma-ray burst, implying stable neutron star remnants are not rare.

Findings

Non-thermal PWN emission fits the afterglow data well

Stable massive neutron star formation may be common in DNS mergers

Supports a stiff equation of state for post-merger neutron stars

Abstract

Mergers of double neutron stars (DNSs) could lead to the formation of a long-lived massive remnant NS, which has been previously suggested to explain the AT 2017gfo kilonova emission in the famous GW170817 event. For an NS-affected kilonova, it is expected that a non-thermal emission component can be contributed by a pulsar wind nebula (PWN), which results from the interaction of the wind from the remnant NS with the preceding merger ejecta. Then, the discovery of such a non-thermal PWN emission can provide an evidence for the existence of the remnant NS. Similar to GRB 170817A, GRB 160821B is also one of the nearest short gamma-ray bursts (SGRBs). A candidate kilonova is widely believed to appear in the ultraviolet-optical-infrared afterglows of GRB 160821B. Here, by modeling the afterglow light curves and spectra of GRB 160821B, we find that the invoking of a non-thermal PWN emission can indeed be well consistent with the observational data. This may indicate that the formation of a stable massive NS could be not rare in the DNS merger events and, thus, the equation of state of the post-merger NSs should be stiff enough.