X-ray emission from the gravitational wave transient GW170817 is well described as non-thermal afterglow radiation produced by a structured relativistic jet viewed off-axis. We show that the X-ray counterpart continues to be detected at 3.3 years after the merger. Such long-lasting signal is not a prediction of the earlier jet models characterized by a narrow jet core and a viewing angle ≈20 deg, and is spurring a renewed interest in the origin of the X-ray emission. We present a comprehensive analysis of the X-ray dataset aimed at clarifying existing discrepancies in the literature, and in particular the presence of an X-ray rebrightening at late times. Our analysis does not find evidence for an increase in the X-ray flux, but confirms a growing tension between the observations and the jet model. Further observations at radio and X-ray wavelengths would be critical to break the degeneracy between models.

Original languageEnglish
Pages (from-to)1902-1909
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date4 Dec 2021
Publication statusPublished - 28 Feb 2022

Bibliographical note

Funding Information:
ET and BO were supported in part by the National Aeronautics and Space Administration (NASA) through grants NNX16AB66G, NNX17AB18G, and 80NSSC20K0389. ET further acknowledges support from the National Science Foundation (NSF) award 2108950. LP and HJvE acknowledge support from the European Union’s Horizon 2020 Programme under the AHEAD2020 project (grant agreement number 871158). LP was supported in part from MIUR, PRIN 2017 (grant 20179ZF5KS). TP was supported by an advanced ERC grant TReX.

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


  • gamma-ray burst
  • gravitational waves
  • stars: neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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