The optical afterglow of the short gamma-ray burst associated with GW170817
journal contribution
posted on 2018-06-11, 08:54 authored by J. D. Lyman, G. P. Lamb, A. J. Levan, I. Mandel, N. R. Tanvir, S. Kobayashi, B. Gompertz, J. Hjorth, A. S. Fruchter, T. Kangas, D. Steeghs, I. A. Steele, Z. Cano, C. Copperwheat, P. A. Evans, J. P. U. Fynbo, C. Gall, M. Im, L. Izzo, P. Jakobsson, B. Milvang-Jensen, P. O'Brien, J. P. Osborne, E. Palazzi, D. A. Perley, E. Pian, S. Rosswog, A. Rowlinson, S. Schulze, E. R. Stanway, P. Sutton, C. C. Thöne, A. D. U. Postigo, D. J. Watson, K. Wiersema, R. A. M. J. WijersThe 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.
Funding
s Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. These observations are associated with programs GO 14771 (Tanvir), GO 14270 (Levan). We thank the staff at STScI for their excellent support of these observations. AJL acknowledges that this project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no 725246). JDL, AJL, DS, KW acknowledge support from STFC via grant ST/P000495/1. NRT, PTO, JPO, GPL, IM, SK acknowledge support from STFC. GPL acknowledges partial support from RAS and IAU grants. JH was supported by a VILLUM FONDEN Investigator grant (project number 16599). The Cosmic Dawn Center is funded by the DNRF. AdUP, CT and ZC acknowledge support from the Spanish project AYA 2014-58381-P. ZC also acknowledges support from the Juan de la Cierva Incorporacion fellowship IJCI-2014-21669. MI acknowledges the support from the ´ NRFK grant, No. 2017R1A3A3001362. SR has been supported by the Swedish Research Council (VR) under grant number 2016- 03657 3, by the Swedish National Space Board under grant number Dnr. 107/16 and by the research environment grant “Gravitational Radiation and Electromagnetic Astrophysical Transients (GREAT)” funded by the Swedish Research council (VR) under Dnr 2016-06012. PAE acknowledges UKSA support. DJW is supported by the the Danish Agency for Science, Technology and Innovation under grant number DFF 7014-00017
History
Citation
Nature Astronomy, 2018Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and AstronomyVersion
- AM (Accepted Manuscript)
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Nature AstronomyPublisher
Nature Publishing Groupeissn
2397-3366Copyright date
2018Available date
2019-01-02Publisher DOI
Publisher version
https://www.nature.com/articles/s41550-018-0511-3Notes
Data Availability The newly-presented HST data are stored in the Mikulski Archive for Space Telescopes (https://archive.stsci.edu/hst/) 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 (http://dfm.io/emcee/current/). 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.Language
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