@article{5fb66e8d2fe8430ea9c46ac8e6fb7163,
title = "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 Lx 3.2 ×1038 erg s-1 (isotropic-equivalent). Continued monitoring revealed the presence of an X-ray source that brightened with time, reaching Lx 9 ×10 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 Ek ∼ 10 erg49-50erg, viewed off-axis with θobs ∼ 20°-40°. Our models favor a circumbinary density n ∼ 10-4-10-2 cm-3, depending on the value of the microphysical parameter ϵB =10-4-10-2. A centralengine 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 θobs are testable with GW information on GW170817 from advanced LIGO/Virgo on the binary inclination.",
keywords = "gravitational waves, relativistic processes, stars: neutron",
author = "R. Margutti and E. Berger and W. Fong and C. Guidorzi and Alexander, {K. D.} and Metzger, {B. D.} and Blanchard, {P. K.} and Cowperthwaite, {P. S.} and R. Chornock and T. Eftekhari and M. Nicholl and Villar, {V. A.} and Williams, {P. K.G.} and J. Annis and Brown, {D. A.} and H. Chen and Z. Doctor and Frieman, {J. A.} and Holz, {D. E.} and M. Sako and M. Soares-Santos",
note = "Funding Information: Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO7-18024X issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. W.F. acknowledges support for program number HST-HF2-51390.001-A, provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. C.G. acknowledges University of Ferrara for use of the local HPC facility co-funded by the “Large-Scale Facilities 2010” project (grant 7746/2011). Development of the Boxfit code was supported in part by NASA through grant NNX10AF62G issued through the Astrophysics Theory Program and by the NSF through grant AST-1009863. The Berger Time-Domain Group at Harvard is supported in part by the NSF through grants AST-1411763 and AST-1714498, and by NASA through grants NNX15AE50G and NNX16AC22G. D.A.B. is supported by NSF award PHY-1707954. Simulations for BOXFITv2 have been carried out in part on the computing facilities of the Computational Center for Particle and Astrophysics of the research cooperation “Excellence Cluster Universe” in Garching, Germany. Publisher Copyright: {\textcopyright} 2017 The American Astronomical Society. All rights reserved.",
year = "2017",
month = oct,
day = "20",
doi = "10.3847/2041-8213/aa9057",
language = "English (US)",
volume = "848",
journal = "Astrophysical Journal Letters",
issn = "2041-8205",
publisher = "IOP Publishing Ltd.",
number = "2",
}