A Strong Jet Signature in the Late-time Light Curve of GW170817
We present new 0.6–10 GHz observations of the binary neutron star merger GW170817 covering the period up to 300 days post-merger, taken with the upgraded Karl G. Jansky Very Large Array, the Australia Telescope Compact Array, the Giant Metrewave Radio Telescope and the MeerKAT telescope. We use these data to precisely characterize the decay phase of the late-time radio light curve. We find that the temporal decay is consistent with a power-law slope of t^(−2.2), and that the transition between the power-law rise and decay is relatively sharp. Such a slope cannot be produced by a quasi-isotropic (cocoon-dominated) outflow, but is instead the classic signature of a relativistic jet. This provides strong observational evidence that GW170817 produced a successful jet, and directly demonstrates the link between binary neutron star mergers and short-hard gamma-ray bursts. Using simple analytical arguments, we derive constraints on the geometry and the jet opening angle of GW170817. These results are consistent with those from our companion very long baseline interferometry paper, reporting superluminal motion in GW170817.
© 2018 The American Astronomical Society. Received 2018 August 30; revised 2018 October 17; accepted 2018 October 29; published 2018 November 16. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Australia Telescope is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. We thank the staff of the GMRT that made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, (SARAO), which is a facility of the National Research Foundation (NRF), an agency of the Department of Science and Technology. The authors thank the NRAO staff, especially Mark Claussen and Amy Mioduszewski, for scheduling the VLA observations. K.P.M. would like to thank Kenta Hotokezaka and Michael Zhang for help with emcee. We thank Varun Bhalerao for help with some of the uGMRT observation A.C. acknowledges support from the NSF CAREER award #1455090. D.D. is supported by an Australian Government Research Training Program Scholarship. K.P.M. is currently a Jansky Fellow of the National Radio Astronomy Observatory. T.M. acknowledges the support of the Australian Research Council through grant FT150100099. Part of this work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant No. 1545949. DK was additionally supported by by NSF grant AST-1412421. P.C. acknowledges support from the Department of Science and Technology via Swarana Jayanti Fellowship award (file no.DST/SJF/PSA-01/2014-15). The research of O.S. is supported by the South African Research Chairs Initiative of the Department of Science and Technology and NRF. Software: Matplotlib (Hunter 2007), NumPy (Oliphant 2006), MIRIAD (Sault et al. 1995), DIFMAP (Shepherd 1997), CASA (McMullin et al. 2007), emcee (Foreman-Mackey et al. 2013), corner (Foreman-Mackey 2016).
Accepted Version - 1810.12927.pdf
Published - Mooley_2018_ApJL_868_L11.pdf