The merger of two dense stellar remnants including at least one neutron star is predicted to produce gravitational waves (GWs) and short-duration gamma ray bursts1,2. In the process, neutron-rich material is ejected from the system and heavy elements are synthesized by r-process nucleosynthesis1,3. The radioactive decay of these heavy elements produces additional transient radiation termed kilonova or macronova4,5,6,7,8,9,10. We report the detection of linear optical polarization, P = (0.50 ± 0.07)%, 1.46 days after detection of the GWs from GW 170817—a double neutron star merger associated with an optical macronova counterpart and a short gamma ray burst11,12,13,14. The optical emission from a macronova is expected to be characterized by a blue, rapidly decaying component and a red, more slowly evolving component due to material rich in heavy elements—the lanthanides15. The polarization measurement was made when the macronova was still in its blue phase, during which there was an important contribution from a lanthanide-free outflow. The low degree of polarization is consistent with intrinsically unpolarized emission scattered by galactic dust, suggesting a symmetric geometry of the emitting region and low inclination of the merger system. Stringent upper limits to the polarization degree from 2.45–9.48 days post-burst are consistent with the lanthanides-rich macronova interpretation.

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  • Correction 30 October 2017

    In the version of this Letter originally published, in the third paragraph of the text Kyutoku  et al. were not correctly cited and the sentence should have read: “As pointed out by Kyutoku at al.28, in the case of high optical depth to electron scattering (~1) and assuming spectral lines do not significantly depolarize the global emission, the linear polarization observed from the equatorial plane could be as high as a few per cent.” Also, in the Author contributions section, the final sentence should have read: “C.G.M. contributed to the writing of the paper.”


  1. 1.

    Eichler, D., Livio, M., Piran, T. & Schramm, D. N. Nucleosynthesis, neutrino bursts and gamma-rays from coalescing neutron stars. Nature 340,126–128 (1989).

  2. 2.

    Berger, E. Short-duration gamma-ray bursts. Annu. Rev. Astron. Astrophys. 52, 43–105 (2014).

  3. 3.

    Rosswog, S. et al. Mass ejection in neutron star mergers. Astron. Astrophys. 341, 499–526 (1999).

  4. 4.

    Li, L.-X. & Paczyński, B. Transient events from neutron star mergers. Astrophys. J. 507, L59–L62 (1998).

  5. 5.

    Rosswog, S. Mergers of neutron star-black hole binaries with small mass ratios: nucleosynthesis, gamma-ray bursts, and electromagnetic transients. Astrophys. J. 634, 1202–1213 (2005).

  6. 6.

    Metzger, B. D. et al. Electromagnetic counterparts of compact object mergers powered by the radioactive decay of r-process nuclei. Mon. Not. R. Astron. Soc. 406, 2650–2662 (2010).

  7. 7.

    Kasen, D., Badnell, N. R. & Barnes, J. Opacities and spectra of the r-process ejecta from neutron star mergers. Astrophys. J. 774, 25 (2013).

  8. 8.

    Barnes, J. & Kasen, D. Effect of a high opacity on the light curves of radioactively powered transients from compact object mergers. Astrophys. J. 775, 18 (2013).

  9. 9.

    Tanaka, M. & Hotokezaka, K. Radiative transfer simulations of neutron star merger ejecta. Astrophys. J. 775, 113 (2013).

  10. 10.

    Baiotti, L. & Rezzolla, L. Binary neutron star mergers: a review of Einstein’s richest laboratory. Rep. Prog. Phys. 80, 096901 (2017).

  11. 11.

    Abbott, B. P. et al. (LIGO Scientific Collaboration and Virgo Collaboration) GW170817: Observation of gravitational waves from a binary neutron star inspiral. Phys. Rev. Lett. https://doi.org/10.1103/PhysRevLett.119.161101 (2017).

  12. 12.

    Savchenko, V. et al. INTEGRAL detection of the first prompt gamma-ray signal coincident with the gravitational event GW170817. Astrophys. J. Lett. https://doi.org/10.3847/2041-8213/aa8f94 (2017).

  13. 13.

    Goldstein et al. An ordinary short gamma-ray burst with extraordinary implications: Fermi-GBM detection of GRB 170817A. Astrophys. J. Lett. https://doi.org/10.3847/2041-8213/aa8f41 (2017).

  14. 14.

    Coulter, D. et al. Swope Supernova Survey 2017a (SSS17a), the optical counterpart to a gravitational wave source. Science https://doi.org/10.1126/science.aap9811 (2017).

  15. 15.

    Kasen, D., Fernàndez, R. & Metzger, B. D. Kilonova light curves from the disc wind outflows of compact object mergers. Mon. Not. R. Astron. Soc. 450, 1777–1786 (2015).

  16. 16.

    Pian, E. et al. Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger. Nature https://doi.org/10.1038/nature24298 (2017).

  17. 17.

    Tanvir, N. R. et al. A 'kilonova' associated with the short-duration γ-ray burst GRB 130603B. Nature 500, 547–549 (2013).

  18. 18.

    Yang, B. et al. A possible macronova in the late afterglow of the ‘long-short’ burst GRB 060614. Nat. Commun. 6, 7323 (2015).

  19. 19.

    Jin, Z.-P. et al. The light curve of the macronova associated with the long-short burst GRB 060614. Astrophys. J. 811, L22 (2015).

  20. 20.

    Jin, Z.-P. et al. The macronova in GRB 050709 and the GRB–macronova connection. Nat. Commun. 7, 12898 (2016).

  21. 21.

    Ghirlanda, G. et al. Short gamma-ray bursts at the dawn of the gravitational wave era. Astron. Astrophys. 594, A84 (2016).

  22. 22.

    Jin, Z.-P. et al. Short GRBs with small opening angles: implications on local neutron star merger rate and GRB/GW association. Preprint athttps://arxiv.org/abs/1708.07008 (2017).

  23. 23.

    Mundell, C. G. et al. Highly polarized light from stable ordered magnetic fields in GRB 120308A. Nature 504, 119–121 (2013).

  24. 24.

    Wiersema, K. et al. Circular polarization in the optical afterglow of GRB 121024A. Nature 509, 201–204 (2014).

  25. 25.

    Goriely, S., Bauswein, A. & Janka, H.-T. r-process nucleosynthesis in dynamically ejected matter of neutron star mergers. Astrophys. J. 738, L32 (2011).

  26. 26.

    Hotokezaka, K. et al. Remnant massive neutron stars of binary neutron star mergers: evolution process and gravitational waveform. Phys. Rev. D 88, 044026 (2013).

  27. 27.

    Kiuchi, K., Cerdà-Duràn, P., Kyutoku, K., Sekiguchi, Y. & Shibata, M. Efficient magnetic- field amplification due to the Kelvin–Helmholtz instability in binary neutron star mergers. Phys. Rev. D 92, 124034 (2015).

  28. 28.

    Kyutoku, K., Ioka, K., Okawa, H., Shibata, M. & Taniguchi, K. Dynamical mass ejection from black hole-neutron star binaries. Phys. Rev. D 92, 044028 (2015).

  29. 29.

    Tanaka, M. et al. Radioactively powered emission from black hole-neutron star mergers. Astrophys. J. 780, 31 (2014).

  30. 30.

    Granot, J., Panaitescu, A., Kumar, P. & Woosley, S. E. Off-axis afterglow emission from jetted gamma-ray bursts. Astrophys. J. 570, L61–L64 (2002).

  31. 31.

    Aasi, J. et al. Characterization of the LIGO detectors during their sixth science run. Classical and Quantum Gravity 32, 074001 (2015).

  32. 32.

    Acernese, F. et al. Advanced Virgo: a second-generation interferometric gravitational wave detector. Class. Quantum Grav. 32, 024001 (2015).

  33. 33.

    Serkowski, K., Mathewson, D. S. & Ford, V. L. Wavelength dependence of interstellar polarization and ratio of total to selective extinction. Astrophys. J. 196, 261–290 (1975).

  34. 34.

    Plaszczynski, S., Montier, L., Levrier, F. & Tristram, M. A novel estimator of the polarization amplitude from normally distributed Stokes parameters. Mon. Not. R. Astron. Soc. 439, 4048–4056 (2014).

  35. 35.

    Wiersema, K. et al. Detailed optical and near-infrared polarimetry, spectroscopy and broad-band photometry of the afterglow of GRB 091018: polarization evolution. Mon. Not. R. Astron. Soc. 426, 2–22 (2012).

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This study was based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under European Southern Observatory programme 099.D-0116. We thank the European Southern Observatory—Paranal staff for carrying out excellent observations under difficult conditions during a hectic period. We also acknowledge partial funding from Agenzia Spaziale Italiana-Istituto Nazionale di Astrofisica grant I/004/11/3. K.W., A.B.H., R.L.C.S. and N.R.T. acknowledge funding from the Science and Technology Facilities Council. J.H. was supported by a VILLUM FONDEN Investigator grant (project number 16599). Y.Z.F. was supported by the National Natural Science Foundation of China under grant 11525313. C.G.M. acknowledges support from the UK Science and Technology Facilities Council. K.T. was supported by Japan Society for the Promotion of Science grant 15H05437 and a Japan Science and Technology Consortia grant. J.M. acknowledges the National Natural Science Foundation of China 11673062 and the Major Program of the Chinese Academy of Sciences(KJZD-EW-M06).

Author information


  1. Istituto Nazionale di Astrofisica / Brera Astronomical Observatory, via Bianchi 46, 23807, Merate (LC), Italy

    • S. Covino
    • , A. Melandri
    • , P. D’Avanzo
    • , M. G. Bernardini
    • , S. Campana
    • , W. Gao
    •  & G. Tagliaferri
  2. Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK

    • K. Wiersema
    • , A. B. Higgins
    • , N. R. Tanvir
    •  & R. L. C. Starling
  3. Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210008, China

    • Y. Z. Fan
    •  & Z. P. Jin
  4. Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, 980-8578, Japan

    • K. Toma
  5. Astronomical Institute, Tohoku University, Sendai, 980-8578, Japan

    • K. Toma
  6. Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, UK

    • C. G. Mundell
  7. Istituto Nazionale di Astrofisica / Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, Via Gobetti 101, 40129, Bologna, Italy

    • E. Palazzi
    • , E. Pian
    •  & A. Rossi
  8. Laboratoire Univers et Particules de Montpellier, Université de Montpellier, Centre National de la Recherche Scientifique / IN2P3, Montpellier, 34095, France

    • M. G. Bernardini
  9. Gran Sasso Science Institute, 67100, L’Aquila, Italy

    • M. Branchesi
  10. Istituto Nazionale di Fisica Nucleare / Laboratori Nazionali del Gran Sasso, 67100, L’Aquila, Italy

    • M. Branchesi
  11. Istituto Nazionale di Astrofisica / Osservatorio Astronomico di Roma, Via di Frascati, 33, 00078, Monteporzio Catone, Italy

    • E. Brocato
  12. Istituto Nazionale di Astrofisica / Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Firenze, Italy

    • S. di Serego Alighieri
  13. Commissariat à l’Énergie Atomique Saclay—Direction de la Recherche Fondamentale/Irfu/Dèpartement d’Astrophysique, 91191, Gif-sur-Yvette, France

    • D. Götz
  14. Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100, Copenhagen, Denmark

    • J. P. U. Fynbo
    • , J. Hjorth
    •  & D. Malesani
  15. Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing, 210046, China

    • W. Gao
  16. Centre for Astrophysics and Cosmology, University of Nova Gorica, Vipavska 11c, 5270, Ajdovščina, Slovenia

    • A. Gomboc
  17. Space Telescope Science Institute, Baltimore, MD, 21218, USA

    • B. Gompertz
  18. Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr. 1, 85748, Garching, Germany

    • J. Greiner
  19. Anton Pannekoek Institute, University of Amsterdam, Science Park 904, 1098XH, Amsterdam, The Netherlands

    • L. Kaper
    •  & R. A. M. J. Wijers
  20. Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778, Tautenburg, Germany

    • S. Klose
  21. Astrophysics Research Institute, Liverpool John Moores University, ic2, Liverpool Science Park, 146 Brownlow Hill, Liverpool, L3 5RF, UK

    • S. Kobayashi
    •  & I. Steele
  22. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000, Ljubljana, Slovenia

    • D. Kopac
  23. Department of Physics, University of Warwick, Coventry, CV4 7AL, UK

    • A. J. Levan
  24. Yunnan Observatories, Chinese Academy of Sciences, 650011, Kunming, Yunnan Province, China

    • J. Mao
  25. Istituto Nazionale di Astrofisica / Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, via E. Bassini 15, 20133, Milano, Italy

    • R. Salvaterra
  26. Department of Astronomy, University of Maryland, College Park, MD, 20742, USA

    • E. Troja
  27. Department of Physics, The George Washington University, 725 21st Street NW, Washington, DC, 20052, USA

    • C. Kouveliotou
    •  & A. J. van der Horst
  28. Astronomy, Physics, and Statistics Institute of Sciences, Washington, DC, 20052, USA

    • A. J. van der Horst


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All authors contributed to the work presented in this paper. S.C. and K.W. coordinated the data acquisition, analysed the data and wrote the paper. A.B.H., A.M., P.D., E.P. and N.T. contributed to the data analysis. Y.F. and K.T. contributed to the theoretical discussion. C.G.M. contributed to the writing of the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to S. Covino.

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