A Radio Counterpart to a Neutron Star Merger

TL;DR

This paper reports the detection of a radio counterpart to the neutron star merger GW170817, providing insights into the merger's energetics and environment through radio observations and modeling.

Contribution

It presents the first radio detection of a neutron star merger counterpart and discusses how future observations can distinguish between different emission models.

Findings

Radio emission detected 16 days post-merger

Emission consistent with off-axis jet or mildly relativistic ejecta

Future observations will clarify the merger's geometry and energetics

Abstract

Gravitational waves have been detected from a binary neutron star merger event, GW170817. The detection of electromagnetic radiation from the same source has shown that the merger occurred in the outskirts of the galaxy NGC 4993, at a distance of 40 megaparsecs from Earth. We report the detection of a counterpart radio source that appears 16 days after the event, allowing us to diagnose the energetics and environment of the merger. The observed radio emission can be explained by either a collimated ultra-relativistic jet viewed off-axis, or a cocoon of mildly relativistic ejecta. Within 100 days of the merger, the radio light curves will distinguish between these models and very long baseline interferometry will have the capability to directly measure the angular velocity and geometry of the debris.