@article{3940c074189d4bd1985e2287d1136b2a,
title = "Measuring the Viewing Angle of GW170817 with Electromagnetic and Gravitational Waves",
abstract = "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.",
keywords = "binaries: close, gravitational waves, stars: neutron",
author = "Daniel Finstad and Soumi De and Brown, {Duncan A.} and Edo Berger and Biwer, {Christopher M.}",
note = "Funding Information: We thank Stefan Ballmer and Steven Reyes for useful discussions. We particularly thank Collin Capano and Alexander Nitz, who made significant contributions to the development of the PyCBC Inference software used in this Letter. This work was supported by U.S. National Science Foundation awards PHY-1404395 (D.A.B., C.M.B.), PHY-1707954 (D.A.B., S.D., D.F.) and AST-1714498 (E.B.). Computational work was supported by Syracuse University and National Science Foundation award OAC-1541396. D.A.B., E.B., and S.D. acknowledge the Kavli Institute for Theoretical Physics which is supported by the National Science Foundation award PHY-1748958. All software used in this analysis is open source and available from https:// github.com/gwastro/pycbc. Full posterior data samples from the MCMC are available at https://github.com/sugwg/gw170817-inclination-angle. The gravitational-wave data used in this work was obtained from the LIGO Open Science Center at https:// losc.ligo.org. LOSC is a service of LIGO Laboratory, the LIGO Scientific Collaboration and the Virgo Collaboration. LIGO is funded by the National Science Foundation. Virgo is funded by the French Centre National de Recherche Scientifique (CNRS), the Italian Istituto Nazionale della Fisica Nucleare (INFN) and the Dutch Nikhef, with contributions by Polish and Hungarian institutes. Publisher Copyright: {\textcopyright} 2018. The American Astronomical Society. All rights reserved.",
year = "2018",
month = jun,
day = "10",
doi = "10.3847/2041-8213/aac6c1",
language = "English (US)",
volume = "860",
journal = "Astrophysical Journal Letters",
issn = "2041-8205",
publisher = "IOP Publishing Ltd.",
number = "1",
}