Tight multimessenger constraints on the neutron star equation of state from GW170817 and a forward model for kilonova light-curve synthesis

Matt Nicholl, Ben Margalit, Patricia Schmidt, Graham P. Smith, Evan J. Ridley, James Nuttall

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53 Scopus citations


We present a rapid analytic framework for predicting kilonova light curves following neutron star (NS) mergers, where the main input parameters are binary-based properties measurable by gravitational wave detectors (chirp mass and mass ratio, orbital inclination) and properties dependent on the nuclear equation of state (tidal deformability, maximum NS mass). This enables synthesis of a kilonova sample for any NS source population, or determination of the observing depth needed to detect a live kilonova given gravitational wave source parameters in low latency. We validate this code, implemented in the public mosfit package, by fitting it to GW170817. A Bayes factor analysis overwhelmingly (B > 1010) favours the inclusion of an additional luminosity source in addition to lanthanide-poor dynamical ejecta during the first day. This is well fit by a shock-heated cocoon model, though differences in the ejecta structure, opacity or nuclear heating rate cannot be ruled out as alternatives. The emission thereafter is dominated by a lanthanide-rich viscous wind. We find the mass ratio of the binary is q = 0.92 ± 0.07 (90 per cent credible interval). We place tight constraints on the maximum stable NS mass, MTOV$=2.17^{+0.08}_{-0.11}$ M⊙. For a uniform prior in tidal deformability, the radius of a 1.4-M⊙ NS is R1.4 ∼10.7 km. Re-weighting with a prior based on equations of state that support our credible range in MTOV, we derive a final measurement R1.4$=11.06^{+1.01}_{-0.98}$ km. Applying our code to the second gravitationally detected NS merger, GW190425, we estimate that an associated kilonova would have been fainter (by ∼0.7 mag at 1 d post-merger) and declined faster than GW170817, underlining the importance of tuning follow-up strategies individually for each GW-detected NS merger.

Original languageEnglish (US)
Pages (from-to)3016-3032
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Aug 1 2021
Externally publishedYes

Bibliographical note

Funding Information:
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 948381). BM is supported by NASA through the NASA Hubble Fellowship grant #HST-HF2-51412.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. PS is supported by the Dutch Research Council (NWO) Veni Grant No. 680-47-460. GPS acknowledges support from the Science and Technology Facilities Council through grant number ST/N021702/1.

Publisher Copyright:
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.


  • gravitational waves
  • methods: data analysis
  • stars: neutron
  • transients: neutron star mergers


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