The electromagnetic counterpart of the binary neutron star merger LIGO/Virgo GW170817. V. rising X-ray emission from an off-axis jet

Research output: Contribution to journalArticlepeer-review


  • R. Margutti
  • E. Berger
  • W. Fong
  • C. Guidorzi
  • K. D. Alexander
  • B. D. Metzger
  • P. K. Blanchard
  • P. S. Cowperthwaite
  • R. Chornock
  • T. Eftekhari
  • V. A. Villar
  • P. K. G. Williams
  • J. Annis
  • D. A. Brown
  • H. Chen
  • Z. Doctor
  • J. A. Frieman
  • D. E. Holz
  • M. Sako
  • M. Soares-Santos

Colleges, School and Institutes


We report the discovery of rising X-ray emission from the binary neutron star merger event GW170817. This is the first detection of X-ray emission from a gravitational-wave (GW) source. Observations acquired with the Chandra X-ray Observatory (CXO) at t≈ 2.3 days post-merger reveal no significant emission, with {L}x≲ 3.2× {10}38 {erg} {{{s}}}-1 (isotropic-equivalent). Continued monitoring revealed the presence of an X-ray source that brightened with time, reaching {L}x≈ 9× {10}38 {erg} {{{s}}}-1 at ≈ 15.1 days post-merger. We interpret these findings in the context of isotropic and collimated relativistic outflows (both on- and off-axis). We find that the broadband X-ray to radio observations are consistent with emission from a relativistic jet with kinetic energy {E}k̃ {10}49-50 {erg}, viewed off-axis with {θ }{obs}̃ 20^\circ {--}40^\circ . Our models favor a circumbinary density ñ {10}-4{--}{10}-2 {{cm}}-3, depending on the value of the microphysical parameter {∊ }B={10}-4{--}{10}-2. A central-engine origin of the X-ray emission is unlikely. Future X-ray observations at t≳ 100 days, when the target will be observable again with the CXO, will provide additional constraints to solve the model degeneracies and test our predictions. Our inferences on {θ }{obs} are testable with GW information on GW170817 from advanced LIGO/Virgo on the binary inclination....


Original languageEnglish
Article numberL20
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 16 Oct 2017


  • stars: neutron, gravitational waves, relativistic processes