First Multimessenger Observations of a Neutron Star Merger

TL;DR

This paper reports the first combined gravitational wave and electromagnetic observations of a neutron star merger, confirming its role in short gamma-ray bursts and r-process element production, and providing insights into jet structure and cosmology.

Contribution

It presents the first multimessenger detection of a neutron star merger, linking gravitational waves, gamma rays, optical, X-ray, and radio observations to understand the event's physics.

Findings

Confirmed neutron star mergers as sources of short gamma-ray bursts

Established neutron star mergers as sites of r-process nucleosynthesis

Provided constraints on the neutron star equation of state and universe expansion rate

Abstract

We describe the first observations of the same celestial object with gravitational waves and light. * GW170817 was the first detection of a neutron star merger with gravitational waves. * The detection of a spatially coincident weak burst of $\gamma$-rays (GRB 170817A) 1.7 s after the merger constituted the first electromagnetic detection of a gravitational wave source and established a connection between at least some cosmic short gamma-ray bursts (SGRBs) and binary neutron star mergers. * A fast-evolving optical and near-infrared transient (AT 2017gfo) associated with the event can be interpreted as resulting from the ejection of $\sim$0.05 M$_{\odot}$ of material enriched in r-process elements, finally establishing binary neutron star mergers as at least one source of r-process nucleosynthesis. * Radio and X-ray observations revealed a long-rising source that peaked $\sim$160 d after the merger. Combined with the apparent superluminal motion of the associated VLBI source, these observations show that the merger produced a relativistic structured jet whose core was oriented $\approx$ 20 deg from the line of sight and with properties similar to SGRBs. The jet structure likely results from the jet interaction with the merger ejecta. * The electromagnetic and gravitational wave information can be combined to produce constraints on the expansion rate of the universe and the equation of state of dense nuclear matter. These multimessenger endeavors will be a major emphasis for future work.