The Fate of the Merger Remnant in GW170817 and its Imprint on the Jet Structure

TL;DR

This paper uses numerical simulations to study how the environment and lifetime of the merger remnant influence the structure of jets in neutron star mergers, providing insights into GW170817's jet formation timing.

Contribution

It introduces a model linking jet structure to the merger remnant's lifetime, constraining GW170817's remnant collapse time based on jet observations.

Findings

Jet angular energy distribution depends on remnant lifetime

Estimated remnant lifetime for GW170817 is 1-1.7 seconds

Simulations connect jet structure with merger environment and timing

Abstract

The first neutron star binary merger detected in gravitational waves, GW170817 and the subsequent detection of its emission across the electromagnetic spectrum showed that these systems are viable progenitors of short $\gamma$-ray bursts (sGRB). The afterglow signal of GW170817 has been found to be consistent with a structured GRB jet seen off-axis, requiring significant amounts of relativistic material at large angles. This trait can be attributed to the interaction of the relativistic jet with the external wind medium. Here we perform numerical simulations of relativistic jets interacting with realistic wind environments in order to explore how the properties of the wind and central engine affect the structure of successful jets. We find that the angular energy distribution of the jet depends primarily on the ratio between the lifetime of the jet and the time it takes the merger remnant to collapse. We make use of these simulations to constrain the time it took for the merger remnant in GW170817 to collapse into a black hole based on the angular structure of the jet as inferred from afterglow observations. We conclude that the lifetime of the merger remnant in GW170817 was $\approx 1-1.7$s, which, after collapse, triggered the formation of the jet.