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The X-ray counterpart to the gravitational-wave event GW170817


A long-standing paradigm in astrophysics is that collisions—or mergers—of two neutron stars form highly relativistic and collimated outflows (jets) that power γ-ray bursts of short (less than two seconds) duration1,2,3. The observational support for this model, however, is only indirect4,5. A hitherto outstanding prediction is that gravitational-wave events from such mergers should be associated with γ-ray bursts, and that a majority of these bursts should be seen off-axis, that is, they should point away from Earth6,7. Here we report the discovery observations of the X-ray counterpart associated with the gravitational-wave event GW170817. Although the electromagnetic counterpart at optical and infrared frequencies is dominated by the radioactive glow (known as a ‘kilonova’) from freshly synthesized rapid neutron capture (r-process) material in the merger ejecta8,9,10, observations at X-ray and, later, radio frequencies are consistent with a short γ-ray burst viewed off-axis7,11. Our detection of X-ray emission at a location coincident with the kilonova transient provides the missing observational link between short γ-ray bursts and gravitational waves from neutron-star mergers, and gives independent confirmation of the collimated nature of the γ-ray-burst emission.

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Figure 1: Optical/infrared and X-ray images of the counterpart of GW170817.
Figure 2: Optical and infrared spectra of the kilonova associated with GW170817.
Figure 3: Multi-wavelength light curves for the counterpart of GW170817.
Figure 4: Schematic diagram for the geometry of GW170817.


  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)

    ADS  Google Scholar 

  2. 2

    Kouveliotou, C. et al. Identification of two classes of gamma-ray bursts. Astrophys. J. 413, L101–L104 (1993)

    ADS  CAS  Google Scholar 

  3. 3

    Rezzolla, L. et al. The missing link: merging neutron stars naturally produce jet-like structures and can power short gamma-ray bursts. Astrophys. J. 732, L6 (2011)

    ADS  Google Scholar 

  4. 4

    Gehrels, N. et al. A short γ-ray burst apparently associated with an elliptical galaxy at redshift z = 0.225. Nature 437, 851–854 (2005)

    ADS  CAS  PubMed  Google Scholar 

  5. 5

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

    ADS  Google Scholar 

  6. 6

    Schutz, B. F. Networks of gravitational wave detectors and three figures of merit. Class. Quantum Gravity 28, 125023 (2011)

    ADS  MATH  Google Scholar 

  7. 7

    Rhoads, J. E. How to tell a jet from a balloon: a proposed test for beaming in gamma-ray bursts. Astrophys. J. 487, L1–L4 (1997)

    ADS  Google Scholar 

  8. 8

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

    ADS  Google Scholar 

  9. 9

    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)

    ADS  Google Scholar 

  10. 10

    Piran, T., Nakar, E. & Rosswog, S. The electromagnetic signals of compact binary mergers. Mon. Not. R. Astron. Soc. 430, 2121–2136 (2013)

    ADS  Google Scholar 

  11. 11

    van Eerten, H. J., Zhang, W. & MacFadyen, A. I. Off-axis gamma-ray burst afterglow modeling based on a two-dimensional axisymmetric hydrodynamics simulation. Astrophys. J. 722, 235–247 (2010)

    ADS  Google Scholar 

  12. 12

    LIGO Scientific Collaboration and Virgo Collaboration. GW170817: observation of gravitational waves from a binary neutron star inspiral. Phys. Rev. Lett. (2017)

  13. 13

    Goldstein, A. et al. An ordinary short gamma-ray burst with extraordinary implications: Fermi-GBM detection of GRB 170817A. Astrophys. J. 848, (2017)

    ADS  Google Scholar 

  14. 14

    Savchenko, V. et al. INTEGRAL detection of the first prompt gamma-ray signal coincident with the gravitational wave event GW170817. Astrophys. J. 848, (2017)

    ADS  Google Scholar 

  15. 15

    D’Avanzo, P. et al. A complete sample of bright Swift short gamma-ray bursts. Mon. Not. R. Astron. Soc. 442, 2342–2356 (2014)

    ADS  Google Scholar 

  16. 16

    Coulter, D. A. et al. Swope supernova survey 2017a (SSS17a), the optical counterpart to a gravitational wave source. Science (2017)

    ADS  CAS  PubMed  Google Scholar 

  17. 17

    Evans, P. A. et al. Swift and NuSTAR observations of GW170817: detection of a blue kilonova. Science (2017)

    ADS  CAS  PubMed  Google Scholar 

  18. 18

    Hallinan, G. et al. A radio counterpart to a neutron star merger. Science (2017)

    ADS  CAS  PubMed  Google Scholar 

  19. 19

    Grossman, D., Korobkin, O., Rosswog, S. & Piran, T. The long-term evolution of neutron star merger remnants—II. Radioactively powered transients. Mon. Not. R. Astron. Soc. 439, 757–770 (2014)

    ADS  Google Scholar 

  20. 20

    Kisaka, S., Ioka, K. & Nakar, E. X-ray-powered macronovae. Astrophys. J. 818, 104 (2016)

    ADS  Google Scholar 

  21. 21

    Gao, H., Ding, X., Wu, X.-F., Dai, Z.-G. & Zhang, B. GRB 080503 late afterglow re-brightening: signature of a magnetar-powered merger-nova. Astrophys. J. 807, 163 (2015)

    ADS  Google Scholar 

  22. 22

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

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  23. 23

    Nakar, E. & Piran, T. Detectable radio flares following gravitational waves from mergers of binary neutron stars. Nature 478, 82–84 (2011)

    ADS  CAS  PubMed  Google Scholar 

  24. 24

    Zhang, B. & Meszaros, P. Gamma-ray burst afterglow with continuous energy injection: signature of a highly magnetized millisecond pulsar. Astrophys. J. 552, L35–L38 (2001)

    ADS  Google Scholar 

  25. 25

    Rossi, E. M. & Begelman, M. C. Delayed X-ray emission from fallback in compact-object mergers. Mon. Not. R. Astron. Soc. 392, 1451–1455 (2009)

    ADS  CAS  Google Scholar 

  26. 26

    Piran, T. Gamma-ray bursts and the fireball model. Phys. Rep. 314, 575–667 (1999)

    ADS  Google Scholar 

  27. 27

    Van Eerten, H., van der Horst, A. & MacFadyen, A. Gamma-ray burst afterglow broadband fitting based directly on hydrodynamics simulations. Astrophys. J. 749, 44 (2012)

    ADS  Google Scholar 

  28. 28

    Troja, E. et al. An achromatic break in the afterglow of the short GRB 140903A: evidence for a narrow jet. Astrophys. J. 827, 102 (2016)

    ADS  Google Scholar 

  29. 29

    Lazzati, D. et al. Off-axis prompt X-ray transients from the cocoon of short gamma-ray bursts. Preprint at (2017)

  30. 30

    Wollaeger, R. T . et al. Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers. Preprint at (2017)

  31. 31

    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, (2017)

    ADS  Google Scholar 

  32. 32

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

    ADS  Google Scholar 

  33. 33

    Arnaud, K. A. XSPEC: the first ten years. Astron. Data Analysis Softw. Syst. V 101, 17–20 (1996)

    ADS  Google Scholar 

  34. 34

    Tanvir, N. R. et al. The emergence of a lanthanide-rich kilonova following the merger of two neutron stars. Astrophys. J. ( (2017)

    ADS  Google Scholar 

  35. 35

    Deustua, S. (ed.) WFC3 Data Handbook Version 3.0, (Space Telescope Science Institute (STScI), 2016)

  36. 36

    Gonzaga, S., Hack, W., Fruchter, A. & Mack, J. (eds) The DrizzlePac Handbook (Space Telescope Science Institute (STScI), 2012)

  37. 37

    Deustua, S. E ., Mack, J ., Bajaj, V. & Khandrika, H. WFC3/UVIS Updated 2017 Chip-Dependent Inverse Sensitivity Values. Instrument Science Report WFC3, 14, (Space Telescope Science Institute (STScI), 2017)

  38. 38

    Deustua, S. E ., Mack, J ., Bajaj, V. & Khandrika, H. Hubble Space Telescope IR photometric calibration. (Space Telescope Science Institute (STScI), 2017)

  39. 39

    Mateos, S. et al. High precision X-ray log N–log S distributions: implications for the obscured AGN population. Astron. Astrophys. 492, 51–69 (2008)

    ADS  CAS  Google Scholar 

  40. 40

    Swartz, D. A., Soria, R., Tennant, A. F. & Yukita, M. A complete sample of ultraluminous X-ray source host galaxies. Astrophys. J. 741, 49 (2011)

    ADS  Google Scholar 

  41. 41

    Bellini, A ., Grogin, N. A ., Hathi, N. & Brown, T. M. The Hubble Space Telescope “Program of Last Resort”. Instrument Science Report ACS/WFC 2017-12, (Space Telescope Science Institute (STScI), 2017)

  42. 42

    Levan, A. J. et al. The environment of the binary neutron star merger GW170817. Astrophys. J. 848, (2017)

    ADS  Google Scholar 

  43. 43

    Chambers, K. C. et al. The Pan-STARRS1 surveys. Preprint available at (2016)

  44. 44

    Skrutskie, M. F. et al. The Two Micron All Sky Survey (2MASS). Astron. J. 131, 1163–1183 (2006)

    ADS  Google Scholar 

  45. 45

    Kim, S.-L. et al. KMTNET: a network of 1.6 m wide-field optical telescopes installed at three southern observatories. J. Korean Astron. Soc. 49, 37–44 (2016)

    ADS  Google Scholar 

  46. 46

    Smartt, S. J. et al. A kilonova as the electromagnetic counterpart to a gravitational-wave source. Nature (2017)

    ADS  CAS  PubMed  Google Scholar 

  47. 47

    Pian, E. et al. Spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger. Nature (2017)

    ADS  CAS  PubMed  Google Scholar 

  48. 48

    Drout, M. R. et al. Ultraviolet to near-infrared light curves of GW170817/SSS17a - implications for the r-process. Science (2017)

    ADS  CAS  PubMed  Google Scholar 

  49. 49

    Kasliwal, M. M. et al. Illuminating gravitational waves: a concordant picture of photons from a neutron star merger. Science (2017)

    ADS  CAS  PubMed  Google Scholar 

  50. 50

    Chornock, R. et al. The electromagnetic counterpart of the binary neutron star merger LIGO/VIRGO GW170817. IV. Detection of near-infrared signatures of r-process nucleosynthesis with Gemini-South. Astrophys. J. 848, (2017)

    ADS  Google Scholar 

  51. 51

    Schlafly, E. F. & Finkbeiner, D. P. Measuring reddening with Sloan Digital Sky Survey stellar spectra and recalibrating SFD. Astrophys. J. 737, 103 (2011)

    ADS  Google Scholar 

  52. 52

    Blondin, S. & Tonry, J. Determining the type, redshift, and age of a supernova spectrum. Astrophys. J. 666, 1024–1047 (2007)

    ADS  Google Scholar 

  53. 53

    Patat, F. et al. The metamorphosis of SN 1998bw. Astrophys. J. 555, 900–917 (2001)

    ADS  CAS  Google Scholar 

  54. 54

    Modjaz, M., Liu, Y. Q., Bianco, F. B. & Graur, O. The spectral SN-GRB connection: systematic spectral comparisons between type Ic supernovae and broad-lined type Ic supernovae with and without gamma-ray bursts. Astrophys. J. 832, 108–131 (2016)

    ADS  Google Scholar 

  55. 55

    Sault, R. J., Teuben, P. J. & Wright, M. C. H. A retrospective view of MIRIAD. Astron. Data Anal. Softw. Syst. IV 77, 433 (1995)

    ADS  Google Scholar 

  56. 56

    Kim, D. & Im, M. Optical-near-infrared color gradients and merging history of elliptical galaxies. Astrophys. J. 766, 109–135 (2013)

    ADS  Google Scholar 

  57. 57

    Ogando, R. L. C., Maia, M. A. G., Pellegrini, P. S. & Da Costa, L. N. Line strengths of early-type galaxies. Astron. J. 135, 2424–2445 (2008)

    ADS  CAS  Google Scholar 

  58. 58

    Xie, C., Fang, T., Wang, J., Liu, T. & Jiang, X. On the host galaxy of GRB 150101B and the associated active galactic nucleus. Astrophys. J. 824, L17 (2016)

    ADS  Google Scholar 

  59. 59

    Ryan, G., van Eerten, H., MacFadyen, A. & Zhang, B.-B. Gamma-ray bursts are observed off-axis. Astrophys. J. 799, 3 (2015)

    ADS  Google Scholar 

  60. 60

    Sari, R., Piran, T. & Narayan, R. Spectra and light curves of gamma-ray burst afterglows. Astrophys. J. 497, L17–L20 (1998)

    ADS  Google Scholar 

  61. 61

    van Eerten, H. J. & MacFadyen, A. I. Gamma-ray burst afterglow scaling relations for the full blast wave evolution. Astrophys. J. 747, L30 (2012)

    ADS  Google Scholar 

  62. 62

    Nagakura, H., Hotokezaka, K., Sekiguchi, Y., Shibata, M. & Ioka, K. Jet collimation in the ejecta of double neutron star mergers: a new canonical picture of short gamma-ray bursts. Astrophys. J. 784, L28 (2014)

    ADS  Google Scholar 

  63. 63

    Morsony, B. J., Workman, J. C. & Ryan, D. M. Modeling the afterglow of the possible Fermi-GBM event associated with GW150914. Astrophys. J. 825, L24 (2016)

    ADS  Google Scholar 

  64. 64

    Lazzati, D., Deich, A., Morsony, B. J. & Workman, J. C. Off-axis emission of short γ-ray bursts and the detectability of electromagnetic counterparts of gravitational-wave-detected binary mergers. Mon. Not. R. Astron. Soc. 471, 1652–1661 (2017)

    ADS  CAS  Google Scholar 

  65. 65

    Gottlieb, O ., Nakar, E. & Piran, T. The cocoon emission—an electromagnetic counterpart to gravitational waves from neutron star mergers. Preprint at (2017)

  66. 66

    Rossi, E., Lazzati, D. & Rees, M. Afterglow light curves, viewing angle and the jet structure of γ-ray bursts. Mon. Not. R. Astron. Soc. 332, 945–950 (2002)

    ADS  Google Scholar 

  67. 67

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

    ADS  Google Scholar 

  68. 68

    Troja, E., Rosswog, S. & Gehrels, N. Precursors of short gamma-ray bursts. Astrophys. J. 723, 1711–1717 (2010)

    ADS  CAS  Google Scholar 

  69. 69

    D’Alessio, V., Piro, L. & Rossi, E. M. Properties of X-ray rich gamma ray bursts and X-ray flashes detected with BeppoSAX and Hete-2. Astron. Astrophys. 460, 653–664 (2006)

    ADS  Google Scholar 

  70. 70

    Wollaeger, R. T. et al. Radiation transport for explosive outflows: a multigroup hybrid Monte Carlo method. Astrophys. J. Suppl. Ser. 209, 36 (2013)

    Google Scholar 

  71. 71

    Wollaeger, R. T. & van Rossum, D. R. Radiation transport for explosive outflows: opacity regrouping. Astrophys. J. Suppl. Ser. 214, 28 (2014)

    ADS  Google Scholar 

  72. 72

    van Rossum, D. R. et al. Light curves and spectra from a thermonuclear explosion of a white dwarf merger. Astrophys. J. 827, 128 (2016)

    ADS  Google Scholar 

  73. 73

    Fontes, C. J. et al. Relativistic opacities for astrophysical applications. High Energy Density Phys. 16, 53–59 (2015)

    ADS  CAS  Google Scholar 

  74. 74

    Fontes, C. J . et al. A line-smeared treatment of opacities for the spectra and light curves from macronovae. Preprint at (2017)

  75. 75

    Fontes, C. J. et al. The Los Alamos suite of relativistic atomic physics codes. J. Phys. At. Mol. Opt. Phys. 48, 144014 (2015)

    ADS  Google Scholar 

  76. 76

    Rosswog, S. et al. Detectability of compact binary merger macronovae. Class. Quantum Gravity 34, 104001 (2017)

    ADS  Google Scholar 

  77. 77

    Duflo, J. & Zuker, A. P. Microscopic mass formulas. Phys. Rev. C 52, 23–27 (1995)

    ADS  Google Scholar 

  78. 78

    Barnes, J., Kasen, D., Wu, M.-R. & Martine-Pinedo, G. Radioactivity and thermalization in the ejecta of compact object mergers and their impact on kilonova light curves. Astrophys. J. 829, 110 (2016)

    ADS  Google Scholar 

  79. 79

    Moller, P., Nix, J. R., Myers, W. D. & Swiatecki, W. J. Nuclear ground-state masses and deformations. At. Data Nucl. Data Tables 59, 185 (1995)

    ADS  CAS  Google Scholar 

  80. 80

    Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. Mon. Not. R. Astron. Soc. 344, 1000–1028 (2003)

    ADS  Google Scholar 

  81. 81

    Chabrier, G. Galactic stellar and substellar initial mass function. Publ. Astron. Soc. Pacif. 115, 763–795 (2003)

    ADS  Google Scholar 

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We acknowledge the advice and contribution of N. Gehrels, who was co-investigator of our Chandra and Hubble Space Telescope observing programs. We thank B. Wilkes and the Chandra X-ray Center staff, N. Reid and the Space Telescope Science Institute (STScI) staff, J. Stevens and the CSIRO staff, L. Ferrarese and the Gemini support staff, in particular R. Salinas, M. Andersen, H. Kim, P. Candia and K. Silva. E. Troja thanks Bianca A. Vekstein, A. Bersich and F. Troja for help during the preparation of this manuscript. We thank V. Bajaj (STScI) and S. Hernandez for their assistance with data reduction. Work at LANL was done under the auspices of the National Nuclear Security Administration of the US Department of Energy at Los Alamos National Laboratory (LANL) under contract number DE-AC52-06NA25396. All LANL calculations were performed on LANL Institutional Computing resources. This research used resources provided by the LANL Institutional Computing Program, which is supported by the US Department of Energy National Nuclear Security Administration under contract number DE-AC52-06NA25396. M.I., S.-K.L., J.K., C.C., G.L., and Y.Y. acknowledge support from NRFK grant number 2017R1A3A3001362, funded by the Korean government. Work by C.-U.L. and S.-L.K. was supported by the KASI (Korea Astronomy and Space Science Institute) grant 2017-1-830-03. This research made use of the KMTNet system operated by KASI, and the data were obtained at three Cerro-Tololo Inter-American Observatory host sites in Chile, the South African Astronomical Observatory in South Africa, and the Siding Spring Observatory in Australia. E. Troja acknowledges support from grants GO718062A and HSTG014850001A. R.S.-R. acknowledges support by the Italian Space Agency through contract number 2015-046-R.0 and by the European Union Horizon 2020 Programme under the AHEAD project (grant agreement number 654215). T.S. acknowledges support by MEXT KAKENHI (grant numbers 17H06357 and 17H06362).

Author information




E. Troja, L.P., H.v.E. and O.K. composed the text, with input from all co-authors. E. Troja and T.S. obtained and analysed the Chandra X-ray observations. Hubble Space Telescope observations were obtained, reduced and analysed by E. Troja, O.D.F., R.E.R. Jr and H.G.K. E. Troja, N.R.B., S.B.C., J.B.G. and R.S.-R. obtained, processed and analysed the Gemini data. M.I., C.-U.L., S.-L.K., J.K., C.C., G. L., H.M.L. led the optical imaging with KMTNet. E. Troja, L.P., R.R. and M.H.W. obtained, processed and analysed the Australia Telescope Compact Array observations. R.T.W., O.K., C.L.F. and C.J.F. led the modelling of the kilonova emission. H.v.E., L.P. and E. Troja led the modelling of the GRB and afterglow emission. A.M.W., W.H.L. and J.M.B. contributed to the spectral modelling. M.I., Y.Y. and S.-K.L. led the analysis of the host galaxy. All authors discussed the results and commented on the manuscript.

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Extended data figures and tables

Extended Data Figure 1 Spectral energy distributions of the optical/infrared counterpart.

We can empirically describe the spectral energy distribution and its temporal evolution as the superposition of two blackbody components in linear expansion. A single component provides a good fit at early times (T0 + 0.5 d), but at later times we find that two components (shown by the dashed and dotted lines) with different temperatures and expansion velocities represent a better description of the dataset. The large effective radii (R > 4 × 1014 cm at T0 + 0.5 d) inferred from the blackbody fits imply an average velocity v > 0.2c. Magnitudes are corrected for Galactic extinction along the line of sight51. Data have been shifted for plotting purposes.

Extended Data Figure 2 Models of off-axis afterglows at X-ray and radio energies.

Direct comparison between off-axis light curves for two different jet opening angles θj (15° and 28°). As long as the difference between the viewing angle and the jet angle is maintained, a continuous range of jet angles can be found that is consistent with the observations in X-rays and at radio wavelengths, mostly covering the peak. Dashed lines show light curves computed using the semi-analytic spreading top-hat jet model11 for identical input parameters. Note that the simulated angular fluid profile quickly becomes complex as the jet evolves, and the similarity in light curves to those derived from the top-hat shell illustrate that the global features do not depend strongly on this angular profile. The simulated light curves include synchrotron self-absorption, which was not found to be important for the current parameters. (GW, gravitational wave.)

Extended Data Figure 3 Afterglow modelling for different jet profiles viewed at an angle.

We consider three well known jet profiles: top-hat (dot-dashed line), Gaussian (solid line), and power law (dashed line). A power-law structured jet is not consistent with the lack of afterglow detection at early times. A top-hat jet and a Gaussian structured jet can both describe the afterglow behaviour, and imply a large off-axis angle. The Gaussian jet has the additional advantage of consistently explaining both the prompt γ-rays and the afterglow emission.

Extended Data Figure 4 Kilonova light curves as a function of the viewing angle.

Comparison of the observational data with the synthetic light curves from the two-component axisymmetric radiative transfer model at different viewing angles: 0° (on-axis view); 30°, 60° and 90° (edge-on equatorial view). Our model includes a wind with mass Mw ≈ 0.015M and velocity vw ≈ 0.08c, and dynamical ejecta with mass Mej ≈ 0.002M and velocity vej ≈ 0.2c.

Extended Data Figure 5 Illustrative example of the contamination modelling.

a, Two-dimensional dispersed image at the position of AT 2017gfo. b, Our model describing the emission from NGC 4993, smoothed with a Savitzky–Golay filter in order to remove any high-frequency structure. c, Difference between the data and the model.

Extended Data Figure 6 Broadband spectral energy distribution of NGC 4993.

The model assumes a delayed star-formation rate, standard spectral templates80 and initial mass function81. Models for three different stellar ages are shown. Fluxes are corrected for Galactic extinction along the line of sight51. Vertical error bars are 1σ. Data above 5,000 Å (open circles) are not used in the fit as they may be affected by emission from dust. The modelling of the spectral energy distribution favours a mean stellar age of 3–7 billion years (Gyr) and disfavours ages less than 2 Gyr. The mean stellar mass is found to be in the range of (5–10) × 1010M with a solar metallicity.

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

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