Measuring the Viewing Angle of GW170817 with Electromagnetic and Gravitational Waves

Daniel Finstad, Soumi De, Duncan A. Brown, Edo Berger, Christopher M. Biwer

Research output: Contribution to journalArticlepeer-review

55 Scopus citations


The joint detection of gravitational waves (GWs) and electromagnetic (EM) radiation from the binary neutron star merger GW170817 ushered in a new era of multi-messenger astronomy. Joint GW-EM observations can be used to measure the parameters of the binary with better precision than either observation alone. Here, we use joint GW-EM observations to measure the viewing angle of GW170817, the angle between the binary's angular momentum and the line of sight. We combine a direct measurement of the distance to the host galaxy of GW170817 (NGC 4993) of 40.7 ±2.36 Mpc with the Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo GW data and find that the viewing angle is degrees (90% confidence, statistical, and systematic errors). We place a conservative lower limit on the viewing angle of ≥13°, which is robust to the choice of prior. This measurement provides a constraint on models of the prompt γ-ray and radio/X-ray afterglow emission associated with the merger; for example, it is consistent with the off-axis viewing angle inferred for a structured jet model. We provide for the first time the full posterior samples from Bayesian parameter estimation of LIGO/Virgo data to enable further analysis by the community.

Original languageEnglish (US)
Article numberL2
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Jun 10 2018


  • binaries: close
  • gravitational waves
  • stars: neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Measuring the Viewing Angle of GW170817 with Electromagnetic and Gravitational Waves'. Together they form a unique fingerprint.

Cite this