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Title: The optical afterglow of the short gamma-ray burst associated with GW170817
Authors: Lyman, J. D.
Lamb, G. P.
Levan, A. J.
Mandel, I.
Tanvir, N. R.
Kobayashi, S.
Gompertz, B.
Hjorth, J.
Fruchter, A. S.
Kangas, T.
Steeghs, D.
Steele, I. A.
Cano, Z.
Copperwheat, C.
Evans, P. A.
Fynbo, J. P. U.
Gall, C.
Im, M.
Izzo, L.
Jakobsson, P.
Milvang-Jensen, B.
O'Brien, P.
Osborne, J. P.
Palazzi, E.
Perley, D. A.
Pian, E.
Rosswog, S.
Rowlinson, A.
Schulze, S.
Stanway, E. R.
Sutton, P.
Thöne, C. C.
Postigo, A. D. U.
Watson, D. J.
Wiersema, K.
Wijers, R. A. M. J.
First Published: 2-Jul-2018
Publisher: Nature Publishing Group
Citation: Nature Astronomy, 2018
Abstract: The binary neutron star merger GW170817 was the first multi-messenger event observed in both gravitational and electromagnetic waves. The electromagnetic signal began ~ 2 seconds after the merger with a weak, short burst of gamma-rays, which was followed over the course of the next hours and days by the ultraviolet, optical and near-infrared emission from a radioactively-powered kilonova. The low luminosity of the gamma-rays and the rising radio and X-ray flux from the source at late times could indicate that we are viewing this event outside the opening angle of the beamed relativistic jet launched during the merger. Alternatively, the emission could be arising from a cocoon of material formed from the interaction between a (possibly choked) jet and the merger ejecta. Here we present late-time optical detections and deep near-infrared limits on the emission from GW170817 at 110 days after the merger. Our new observations are at odds with expectations of late-time emission from kilonova models, being too bright and blue. Instead, this late-time optical emission arises from the optical afterglow of GRB 170817A, associated with GW170817. This emission matches the expectations of a structured relativistic jet, that would have launched a high luminosity short GRB to an aligned observer. The distinct predictions for the future optical behaviour in the structured-jet and cocoon models will directly distinguish the origin of the emission.
DOI Link: 10.1038/s41550-018-0511-3
eISSN: 2397-3366
Version: Post-print
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2018, Nature Publishing Group. Deposited with reference to the publisher’s open access archiving policy. (
Description: Data Availability The newly-presented HST data are stored in the Mikulski Archive for Space Telescopes ( and available from the corresponding author upon reasonable request. Code Availability The algorithm for the structured jet model used here is fully described in Ref.22 and the MCMC implementation was done via the publicly available emcee46 package ( The specific codes are available upon request to the corresponding author.
The file associated with this record is under embargo until 6 months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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