• Open Access

Properties of the Binary Neutron Star Merger GW170817

B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)
Phys. Rev. X 9, 011001 – Published 2 January 2019

Abstract

On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a low-mass compact binary inspiral. The initial sky localization of the source of the gravitational-wave signal, GW170817, allowed electromagnetic observatories to identify NGC 4993 as the host galaxy. In this work, we improve initial estimates of the binary’s properties, including component masses, spins, and tidal parameters, using the known source location, improved modeling, and recalibrated Virgo data. We extend the range of gravitational-wave frequencies considered down to 23 Hz, compared to 30 Hz in the initial analysis. We also compare results inferred using several signal models, which are more accurate and incorporate additional physical effects as compared to the initial analysis. We improve the localization of the gravitational-wave source to a 90% credible region of 16deg2. We find tighter constraints on the masses, spins, and tidal parameters, and continue to find no evidence for nonzero component spins. The component masses are inferred to lie between 1.00 and 1.89M when allowing for large component spins, and to lie between 1.16 and 1.60M (with a total mass 2.730.01+0.04M) when the spins are restricted to be within the range observed in Galactic binary neutron stars. Using a precessing model and allowing for large component spins, we constrain the dimensionless spins of the components to be less than 0.50 for the primary and 0.61 for the secondary. Under minimal assumptions about the nature of the compact objects, our constraints for the tidal deformability parameter Λ˜ are (0,630) when we allow for large component spins, and 300230+420 (using a 90% highest posterior density interval) when restricting the magnitude of the component spins, ruling out several equation-of-state models at the 90% credible level. Finally, with LIGO and GEO600 data, we use a Bayesian analysis to place upper limits on the amplitude and spectral energy density of a possible postmerger signal.

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  • Received 6 June 2018
  • Revised 20 September 2018
  • Corrected 30 April 2019

DOI:https://doi.org/10.1103/PhysRevX.9.011001

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Corrections

30 April 2019

Correction: The wrong author-affiliation list was used and has now been fixed.

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Popular Summary

On August 17, 2017, gravitational-wave observatories detected evidence of a long-anticipated class of gravitational-wave sources: the merger of two neutron stars. The event was coincident with a gamma-ray burst and was later detected by instruments across the electromagnetic spectrum. Here, we improve on the initial estimates of the binary’s properties, such as masses, spins, and tidal parameters.

The gravitational-wave signal provides information on the masses and spins of the binary’s components, the distance and location of the source, and the orientation of its orbit. Neutron stars, unlike black holes, can also be tidally deformed. Excitation of tides affects the phase evolution of the signal, allowing us to probe the behavior of matter at ultrahigh densities, the so-called equation of state.

Our improved analysis relies on recalibrated data from the Virgo detector in Italy, knowledge of the source location, and an extended range of gravitational-wave frequencies. The new constraints on mass, spin, and tidal deformation rule out some of the stiffest equations of state, and place new upper limits on a possible postmerger signal. We find evidence for tidal deformation of the components when individual spins are restricted to the range observed in Galactic binaries. However, when allowing for large spins, we cannot rule out the possibility of no tidal deformation, meaning we cannot say from gravitational-wave measurements alone that the components were neutron stars.

With increased sensitivity of the Advanced LIGO and Virgo detectors, we expect more detections of neutron-star mergers within the next several years. Our techniques can be used for future events to constrain the equation of state at supranuclear densities, which governs matter inside neutron stars.

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Vol. 9, Iss. 1 — January - March 2019

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