@article{d806d184bf244cebae787fbf6c5e7ef9,
title = "A Decline in the X-Ray through Radio Emission from GW170817 Continues to Support an Off-axis Structured Jet",
abstract = "We present new observations of the binary neutron star merger GW170817 at Δt ≈ 220-290 days post-merger, at radio (Karl G. Jansky Very Large Array; VLA), X-ray (Chandra X-ray Observatory), and optical (Hubble Space Telescope; HST) wavelengths. These observations provide the first evidence for a turnover in the X-ray light curve, mirroring a decline in the radio emission at 5σ significance. The radio-to-X-ray spectral energy distribution exhibits no evolution into the declining phase. Our full multi-wavelength data set is consistent with the predicted behavior of our previously published models of a successful structured jet expanding into a low-density circumbinary medium, but pure cocoon models with a choked jet cannot be ruled out. If future observations continue to track our predictions, we expect that the radio and X-ray emission will remain detectable until ∼1000 days post-merger.",
keywords = "gravitational waves, relativistic processes",
author = "Alexander, {K. D.} and R. Margutti and Blanchard, {P. K.} and W. Fong and E. Berger and A. Hajela and T. Eftekhari and R. Chornock and Cowperthwaite, {P. S.} and D. Giannios and C. Guidorzi and A. Kathirgamaraju and A. Macfadyen and Metzger, {B. D.} and M. Nicholl and L. Sironi and Villar, {V. A.} and Williams, {P. K.G.} and X. Xie and J. Zrake",
note = "Funding Information: We would like to thank the referee for helpful comments that improved this manuscript. The Berger Time-Domain Group at Harvard is supported in part by the NSF through grant AST-1714498, and by NASA through grants NNX15AE50G and NNX16AC22G. This work is partially based on observations acquired by the Chandra X-ray Observatory. The Chandra X-ray Observatory Center is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. Funding Information: We would like to thank the referee for helpful comments that improved this manuscript. The Berger Time-Domain Group at Harvard is supported in part by the NSF through grant AST-1714498, and by NASA through grants NNX15AE50G and NNX16AC22G. This work is partially based on observations acquired by the Chandra X-ray Observatory. The Chandra X-ray Observatory Center 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 from 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. B.D.M. is supported in part by NASA ATP grant NNX16AB30G. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Facilities: VLA, HST, CXO. Software: CASA, emcee, Numpy, pwkit. Publisher Copyright: {\textcopyright} 2018. The American Astronomical Society. All rights reserved.",
year = "2018",
month = aug,
day = "20",
doi = "10.3847/2041-8213/aad637",
language = "English (US)",
volume = "863",
journal = "Astrophysical Journal Letters",
issn = "2041-8205",
publisher = "IOP Publishing Ltd.",
number = "2",
}