The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. V. Rising X-Ray Emission from an Off-axis Jet
Abstract
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}k∼ {10}49-50 {erg}, viewed off-axis with {θ }{obs}∼ 20^\circ {--}40^\circ . Our models favor a circumbinary density n∼ {10}-4{--}{10}-2 {{cm}}-3, depending on the value of the microphysical parameter {ɛ }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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2017
- DOI:
- 10.3847/2041-8213/aa9057
- arXiv:
- arXiv:1710.05431
- Bibcode:
- 2017ApJ...848L..20M
- Keywords:
-
- stars: neutron;
- gravitational waves;
- relativistic processes;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 7 Pages, 4 Figures, ApJL, In Press. Keywords: GW170817, LVC