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A mildly relativistic wide-angle outflow in the neutron-star merger event GW170817

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GW170817 was the first gravitational wave detection of a binary neutron-star merger1. It was accompanied by radiation across the electromagnetic spectrum and localized2 to the galaxy NGC 4993 at a distance of 40 megaparsecs. It has been proposed that the observed γ-ray, X-ray and radio emission is due to an ultra-relativistic jet launched during the merger, directed away from our line of sight3–6. The presence of such a jet is predicted from models that posit neutron-star mergers as the central engines that drive short hard γ-ray bursts7,8. Here we report that the radio light curve of GW170817 has no direct signature of an off-axis jet afterglow. Although we cannot rule out the existence of a jet pointing elsewhere, the observed γ-rays could not have originated from such a jet. Instead, the radio data require a mildly relativistic wide-angle outflow moving towards us. This outflow could be the high-velocity tail of the neutron-rich material dynamically ejected during the merger or a cocoon of material that breaks out when a jet transfers its energy to the dynamical ejecta. The cocoon model explains the radio light curve of GW170817 as well as the γ-rays and X-rays (possibly also ultraviolet and optical emission)9–15, and is therefore the model most consistent with the observational data. Cocoons may be a ubiquitous phenomenon produced in neutron-star mergers, giving rise to a heretofore unidentified population of radio, ultraviolet, X-ray and γ-ray transients in the local Universe.

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Author information


  1. Hintze Fellow, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK

    • K. P. Mooley
  2. National Radio Astronomy Observatory, Socorro, New Mexico 87801, USA

    • K. P. Mooley
    • , D. A. Frail
    •  & S. T. Myers
  3. California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, California 91125, USA

    • K. P. Mooley
    • , G. Hallinan
    • , K. De
    • , M. M. Kasliwal
    •  & S. R. Kulkarni
  4. The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel

    • E. Nakar
    •  & O. Gottlieb
  5. Department Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, New Jersey 08544, USA

    • K. Hotokezaka
  6. Department of Physics and Astronomy, Texas Tech University, Box 41051, Lubbock, Texas 79409-1051, USA

    • A. Corsi
  7. Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

    • A. Horesh
    •  & T. Piran
  8. Sydney Institute for Astronomy, School of Physics, University of Sydney, New South Wales 2006, Australia

    • T. Murphy
    • , E. Lenc
    • , D. Dobie
    •  & C. Lynch
  9. ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)

    • T. Murphy
    • , E. Lenc
    • , D. Dobie
    •  & C. Lynch
  10. Department of Physics, University of Wisconsin - Milwaukee, Milwaukee, Wisconsin 53201, USA

    • D. L. Kaplan
  11. ATNF, CSIRO Astronomy and Space Science, PO Box 76, Epping, New South Wales 1710, Australia

    • D. Dobie
    •  & K. W. Bannister
  12. National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University Campus, Ganeshkhind Pune 411007, India

    • P. Chandra
  13. Department of Astronomy, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden

    • P. Chandra
  14. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, John Street, Hawthorn, Victoria 3122, Australia

    • A. Deller
  15. Institute of Mathematics, Astrophysics and Particle Physics, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands

    • S. Nissanke
  16. Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India

    • V. Bhalerao
  17. Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, S-439 92 Onsala, Sweden

    • S. Bourke
  18. Astroparticle Physics Laboratory, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, Maryland 20771, USA

    • L. P. Singer


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Corresponding author

Correspondence to K. P. Mooley.


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