The orbit of GW170817 was inclined by less than 28 degrees to the line of sight

TL;DR

This paper combines gravitational-wave data, galaxy redshift, and Hubble constant measurements to constrain the inclination angle of GW170817's binary neutron star merger, finding it to be less than 28 degrees at 90% confidence.

Contribution

It introduces a novel multi-messenger approach to constrain the binary inclination angle using gravitational-wave, electromagnetic, and cosmological data.

Findings

Inclination angle less than 28 degrees at 90% confidence

Provides constraints on models of afterglow observations

Demonstrates the power of combining different observational data

Abstract

We combine the gravitational-wave measurement of the effective distance to the binary neutron star merger GW170817, the redshift of its host galaxy NGC 4993, and the latest Hubble constant measurement from the Dark Energy Survey to constrain the inclination between the orbital angular momentum of the binary and the line of sight to $18 \pm 8$ degrees (less than 28 degrees at 90% confidence). This provides a complementary constraint on models of potential afterglow observations.