Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Superluminal motion of a relativistic jet in the neutron-star merger GW170817

Nature volume 561, pages 355–359 (2018)Cite this article

Subjects

An Author Correction to this article was published on 17 December 2019

This article has been updated

Abstract

The binary neutron-star merger GW1708171 was accompanied by radiation across the electromagnetic spectrum2 and localized2 to the galaxy NGC 4993 at a distance3 of about 41 megaparsecs from Earth. The radio and X-ray afterglows of GW170817 exhibited delayed onset4,5,6,7, a gradual increase8 in the emission with time (proportional to t0.8) to a peak about 150 days after the merger event9, followed by a relatively rapid decline9,10. So far, various models have been proposed to explain the afterglow emission, including a choked-jet cocoon4,8,11,12,13 and a successful-jet cocoon4,8,11,12,13,14,15,16,17,18 (also called a structured jet). However, the observational data have remained inconclusive10,15,19,20 as to whether GW170817 launched a successful relativistic jet. Here we report radio observations using very long-baseline interferometry. We find that the compact radio source associated with GW170817 exhibits superluminal apparent motion between 75 days and 230 days after the merger event. This measurement breaks the degeneracy between the choked- and successful-jet cocoon models and indicates that, although the early-time radio emission was powered by a wide-angle outflow8 (a cocoon), the late-time emission was most probably dominated by an energetic and narrowly collimated jet (with an opening angle of less than five degrees) and observed from a viewing angle of about 20 degrees. The imaging of a collimated relativistic outflow emerging from GW170817 adds substantial weight to the evidence linking binary neutron-star mergers and short γ-ray bursts.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Proper motion of the radio counterpart of GW170817.
Fig. 2: Radio, 3-GHz light curves of several representative simulated models.
Fig. 3: Synthetic radio images.
Fig. 4: Schematic of the physical and geometric parameters derived for GW170817.

Similar content being viewed by others

Data availability

All relevant (VLBI) data are available from the corresponding authors on request. The VLA data (presented in Fig. 2) are currently being readied for public release.

Change history

  • 17 December 2019

    An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

References

  1. Abbott, B. P. et al. GW170817: observation of gravitational waves from a binary neutron star inspiral. Phys. Rev. Lett. 119, 161101 (2017).

    Article  ADS  CAS  Google Scholar 

  2. Abbott, B. P. et al. Multi-messenger observations of a binary neutron star merger. Astrophys. J. 848, L12 (2017).

    Article  ADS  Google Scholar 

  3. Hjorth, J. et al. The distance to NGC 4993: the host galaxy of the gravitational-wave event GW170817. Astrophys. J. 848, L31 (2017).

    Article  ADS  Google Scholar 

  4. Hallinan, G. et al. A radio counterpart to a neutron star merger. Science 358, 1579–1583 (2017).

    Article  ADS  CAS  Google Scholar 

  5. Troja, E. et al. The X-ray counterpart to the gravitational-wave event GW170817. Nature 551, 71–74 (2017).

    Article  ADS  Google Scholar 

  6. Margutti, R. et al. The electromagnetic counterpart of the binary neutron star merger LIGO/Virgo GW170817. V. Rising X-ray emission from an off-axis jet. Astrophys. J. 848, L20 (2017).

    Article  ADS  Google Scholar 

  7. Haggard, D. et al. A deep Chandra X-ray study of neutron star coalescence GW170817. Astrophys. J. 848, L25 (2017).

    Article  ADS  Google Scholar 

  8. Mooley, K. P. et al. A mildly relativistic wide-angle outflow in the neutron-star merger event GW170817. Nature 554, 207–210 (2018).

    Article  ADS  CAS  Google Scholar 

  9. Dobie, D. et al. A turnover in the radio light curve of GW170817. Astrophys. J. 858, L15 (2018).

    Article  ADS  Google Scholar 

  10. Alexander, K. D. et al. A decline in the X-ray through radio emission from GW170817 continues to support an off-axis structured jet. Astrophys. J. 863, L18 (2018).

    Article  ADS  Google Scholar 

  11. Kasliwal, M. M. et al. Illuminating gravitational waves: A concordant picture of photons from a neutron star merger. Science 358, 1559–1565 (2017).

    Article  ADS  CAS  Google Scholar 

  12. Troja, E. et al. The outflow structure of GW170817 from late-time broad-band observations. Mon. Not. R. Astron. Soc. 478, L18–L23 (2018).

    Article  ADS  CAS  Google Scholar 

  13. Xie, X., Zrake, J. & MacFadyen, A. Numerical simulations of the jet dynamics and synchrotron radiation of binary neutron star merger event GW170817/GRB 170817A. Astrophys. J. 863, 58 (2018).

    Article  ADS  Google Scholar 

  14. Lamb, G. P. & Kobayashi, S. Electromagnetic counterparts to structured jets from gravitational wave detected mergers. Mon. Not. R. Astron. Soc. 472, 4953–4964 (2017).

    Article  ADS  CAS  Google Scholar 

  15. Lazzati, D. et al. Late time afterglow observations reveal a collimated relativistic jet in the ejecta of the binary neutron star merger GW170817. Phys. Rev. Lett. 120, 241103 (2018).

    Article  ADS  CAS  Google Scholar 

  16. Margutti, R. et al. The binary neutron star event LIGO/Virgo GW170817 160 days after merger: synchrotron emission across the electromagnetic spectrum. Astrophys. J. 856, L18 (2018).

    Article  ADS  Google Scholar 

  17. Lyman, J. D. et al. The optical afterglow of the short gamma-ray burst associated with GW170817. Nat. Astron. https://doi.org/10.1038/s41550-018-0511-3 (2018).

    Article  ADS  Google Scholar 

  18. Resmi, L. et al. Low frequency view of GW 170817/GRB 170817A with the Giant Meterwave Radio Telescope. Preprint at https://arxiv.org/abs/1803.02768 (2018).

  19. Nakar, E. & Piran, T. Implications of the radio and X-ray emission that followed GW170817. Mon. Not. R. Astron. Soc. 478, 407–415 (2018).

    Article  ADS  CAS  Google Scholar 

  20. Troja, E., Piro, L. & Ryan, G. Chandra observations of GW170817 reveal a fading afterglow. Astron. Telegr. 11619 (2018).

  21. Hotokezaka, K., Kiuchi, K., Shibata, M., Nakar, E. & Piran, T. Synchrotron radiation from the fast tail of dynamical ejecta of neutron star mergers. Preprint at https://arxiv.org/abs/1803.00599 (2018).

  22. D’Avanzo, P. et al. The evolution of the X-ray afterglow emission of GW 170817/ GRB 170817A in XMM-Newton observations. Astron. Astrophys. 613, L1 (2018).

    Article  ADS  Google Scholar 

  23. Gill, R. & Granot, J. Afterglow imaging and polarization of misaligned structured GRB jets and cocoons: breaking the degeneracy in GRB 170817A. Mon. Not. R. Astron. Soc. 478, 4128–4141 (2018).

    Article  ADS  CAS  Google Scholar 

  24. Taylor, G., Frail, D., Berger, E. & Kulkarni, S. High resolution observations of GRB 030329. AIP Conf. Ser. 727, 324–327 (2004).

    Article  ADS  CAS  Google Scholar 

  25. Boutelier, T., Henri, G. & Petrucci, P.-O. The influence of the jet opening angle on the appearance of relativistic jets. Mon. Not. R. Astron. Soc. 418, 1913–1922 (2011).

    Article  ADS  Google Scholar 

  26. Lind, K. R. & Blandford, R. D. Semidynamical models of radio jets: relativistic beaming and source counts. Astrophys. J. 295, 358–367 (1985).

    Article  ADS  Google Scholar 

  27. Hotokezaka, K. et al. A Hubble constant measurement from superluminal motion of the jet in GW170817. Preprint at https://arxiv.org/abs/1806.10596 (2018).

  28. Nakar, E., Gottlieb, O., Piran, T., Kasliwal, M. M. & Hallinan, G. From γ to radio - the electromagnetic counterpart of GW 170817. Preprint at https://arxiv.org/abs/1803.07595 (2018).

  29. Fong, W., Berger, E., Margutti, R. & Zauderer, B. A. A decade of short-duration gamma-ray burst broadband afterglows: energetics, circumburst densities, and jet opening angles. Astrophys. J. 815, 102 (2015).

    Article  ADS  Google Scholar 

  30. Wanderman, D. & Piran, T. The rate, luminosity function and time delay of non-Collapsar short GRBs. Mon. Not. R. Astron. Soc. 448, 3026–3037 (2015).

    Article  ADS  CAS  Google Scholar 

  31. Greisen, E. W. in Information Handling in Astronomy – Historical Vistas (ed. Heck, A.) 109–126 (Kluwer Academic, Dordrecht, 2003).

  32. Shepherd, M. C. Difmap: an interactive program for synthesis imaging. ASP Conf. Ser. 125, 77–84 (1997).

    ADS  Google Scholar 

  33. Condon, J. J. Errors in elliptical Gaussian FITS. Publ. Astron. Soc. Pacif. 109, 166–172 (1997).

    Article  ADS  Google Scholar 

  34. Pradel, N., Charlot, P. & Lestrade, J.-F. Astrometric accuracy of phase-referenced observations with the VLBA and EVN. Astron. Astrophys. 452, 1099–1106 (2006).

    Article  ADS  Google Scholar 

  35. Tzioumis, A. K. et al. VLBI observations at 2.3 GHz of the compact galaxy 1934-638. Astron. J. 98, 36–43 (1989).

    Article  ADS  Google Scholar 

  36. Tingay, S. J., Preston, R. A. & Jauncey, D. L. The subparsec-scale structure and evolution of Centaurus A. II. Continued very long baseline array monitoring. Astron. J. 122, 1697–1706 (2001).

    Article  ADS  Google Scholar 

  37. Gottlieb, O., Nakar, E. & Piran, T. The cocoon emission – an electromagnetic counterpart to gravitational waves from neutron star mergers. Mon. Not. R. Astron. Soc. 473, 576–584 (2018).

    Article  ADS  CAS  Google Scholar 

  38. Gottlieb, O., Nakar, E., Piran, T. & Hotokezaka, K. A cocoon shock breakout as the origin of the γ-ray emission in GW170817. Mon. Not. R. Astron. Soc. 479, 588–600 (2018).

    ADS  CAS  Google Scholar 

  39. Mignone, A. et al. PLUTO: a numerical code for computational astrophysics. Astrophys. J. Suppl. Ser. 170, 228–242 (2007).

    Article  ADS  Google Scholar 

  40. Lazzati, D. et al. Off-axis prompt X-ray transients from the cocoon of short gamma-ray bursts. Astrophys. J. 848, L6 (2017).

    Article  ADS  Google Scholar 

  41. Eichler, D. Testing the viewing angle hypothesis for short GRBs with LIGO events. Astrophys. J. 851, L32 (2017).

    Article  ADS  Google Scholar 

  42. Kathirgamaraju, A., Barniol Duran, R. & Giannios, D. Off-axis short GRBs from structured jets as counterparts to GW events. Mon. Not. R. Astron. Soc. 473, L121–L125 (2018).

    Article  ADS  CAS  Google Scholar 

  43. Bromberg, O., Tchekhovskoy, A., Gottlieb, O., Nakar, E. & Piran, T. The γ-rays that accompanied GW170817 and the observational signature of a magnetic jet breaking out of NS merger ejecta. Mon. Not. R. Astron. Soc. 475, 2971–2977 (2018).

    Article  ADS  CAS  Google Scholar 

  44. Pozanenko, A. S. et al. GRB 170817A associated with GW170817: multi-frequency observations and modeling of prompt gamma-ray emission. Astrophys. J. 852, L30 (2018).

    Article  ADS  Google Scholar 

  45. Granot, J. & Piran, T. On the lateral expansion of gamma-ray burst jets. Mon. Not. R. Astron. Soc. 421, 570–587 (2012).

    ADS  Google Scholar 

  46. Corsi, A. et al. An upper-limit on the linear polarization fraction of the GW170817 radio continuum. Astrophys. J. 861, L10 (2018).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

We are grateful to the VLBA, VLA and GBT staff, especially M. Claussen, A. Mioduszewski, T. Minter, F. Ghigo, W. Brisken, K. O’Neill and M. McKinnon, for their support with the HSA observations. We thank V. Dhawan and P. Demorest for help with observational issues with the VLBI system at the VLA. K.P.M. thanks A. Mioduszewski, E. Momjian, E. Greisen, T. Pearson and S. Kulkarni for discussions. We thank M. Kasliwal for providing comments on the manuscript. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities. K.P.M. is currently a Jansky Fellow of the National Radio Astronomy Observatory. K.P.M. acknowledges support from the Oxford Centre for Astrophysical Surveys, which is funded through the Hintze Family Charitable Foundation, for some initial work presented here. E.N. acknowledges the support of an ERC starting grant (GRB/SN) and an ISF grant (1277/13). A.T.D. is the recipient of an Australian Research Council Future Fellowship (FT150100415). G.H. acknowledges the support of NSF award AST-1654815. A.H. acknowledges support by the I-Core Program of the Planning and Budgeting Committee and the Israel Science Foundation. A.C. acknowledges support from the NSF CAREER award number 1455090 titled ‘CAREER: Radio and gravitational-wave emission from the largest explosions since the Big Bang’.

Author contributions

K.P.M., A.T.D., S.B., G.H. and D.A.F. coordinated the VLBI observations. A.T.D. and K.P.M. performed the VLBI data processing. O.G. and E.N. carried out the theoretical study, including analytic calculations and numerical simulations, with some input from K.H. K.P.M., A.T.D., E.N., G.H. and D.A.F. wrote the paper. A.C. and A.H. compiled the references. A.H., A.D. and K.P.M. compiled Methods. O.G., A.T.D., A.H. and K.P.M. prepared the figures. All co-authors discussed the results and provided comments on the manuscript.

Author information

Author notes

  1. These authors contributed equally: K. P. Mooley, A. T. Deller, O. Gottlieb

Authors and Affiliations

  1. National Radio Astronomy Observatory, Socorro, NM, USA

    K. P. Mooley & D. A. Frail

  2. Caltech, Pasadena, CA, USA

    K. P. Mooley & G. Hallinan

  3. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria, Australia

    A. T. Deller

  4. ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), Hawthorn, Victoria, Australia

    A. T. Deller

  5. The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel

    O. Gottlieb & E. Nakar

  6. Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden

    S. Bourke

  7. Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, Israel

    A. Horesh

  8. Department of Physics and Astronomy, Texas Tech University, Lubbock, TX, USA

    A. Corsi

  9. Department Astrophysical Sciences, Princeton University, Princeton, NJ, USA

    K. Hotokezaka

Authors
  1. K. P. Mooley
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. A. T. Deller
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. O. Gottlieb
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. E. Nakar
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. G. Hallinan
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. S. Bourke
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. D. A. Frail
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. A. Horesh
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. A. Corsi
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. K. Hotokezaka
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding authors

Correspondence to K. P. Mooley or O. Gottlieb.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 VLBI images.

a, b, The cleaned images (natural weighting; 0.2 mas pixel−1) from the two epochs of VLBI, 75 days (a) and 230 days (b) post-merger. The centre coordinates for these images are RA = 13 h 09 min 48.069 s, dec. = −23° 22′ 53.39′. The black contours are at 11, 22 and 44 μJy beam−1 in both images (red dashed contour is −11 μJy beam−1). The peak flux density of the sources is 58 ± 5 μJy beam−1 (a) and 48 ± 6 μJy beam−1 (b) (image root-mean-square noise quoted as the 1σ uncertainty). The ellipse in the lower left corner of each panel shows the synthesized beam: (12.4, 2.2, −7) and (9.1, 3.2, −4) for the two epochs (major axis in mas, minor axis in mas, position angle in degrees).

Extended Data Fig. 2 VLBI astrometric accuracy.

a, b, The VLBI positions of GW170817 (a, relative to the best-fit position at day 75) and the low-luminosity active galactic nucleus in NGC 4993 (b, relative to the previously derived position using VLBA-only observations). The individual observations of GW170817 have very low signal-to-noise ratio and hence large errors; the moderately discrepant measurement on day 72 has the lowest signal-to-noise ratio and was affected by observing issues at the GBT. The NGC 4993 positions do not show any significant systematic position shifts between the two epochs, and are consistent with our estimated systematic position uncertainties of 0.15 mas in RA and 0.5 mas in dec. The root-mean-square variation in the position of the nucleus of NGC 4993 over our seven individual observations (0.14 mas in RA and 0.49 mas in dec.) is shown as a dotted ellipse in b. All error bars and uncertainties quoted are 1σ.

Extended Data Table 1 Log of VLBI (HSA) observations
Full size table
Extended Data Table 2 The initial set-ups of models A–D
Full size table

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Mooley, K.P., Deller, A.T., Gottlieb, O. et al. Superluminal motion of a relativistic jet in the neutron-star merger GW170817. Nature 561, 355–359 (2018). https://doi.org/10.1038/s41586-018-0486-3

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41586-018-0486-3

Keywords

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing