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The optical afterglow of GW170817 at one year post-merger
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Lamb, G. P., Lyman, J. D., Levan, Andrew J., Tanvir, N. R., Kangas, T., Fruchter, A. S., Gompertz, Benjamin P., Hjorth, J., Mandel, I., Oates, S. R., Steeghs, D. and Wiersema, Klaas (2019) The optical afterglow of GW170817 at one year post-merger. The Astrophysical Journal, 870 (2). L15. doi:10.3847/2041-8213/aaf96b ISSN 0004-637X.
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Official URL: http://dx.doi.org/10.3847/2041-8213/aaf96b
Abstract
We present observations of the optical afterglow of GRB 170817A, made by the Hubble Space Telescope, between 2018 February and August, up to one year after the neutron star merger GW170817. The afterglow shows a rapid decline beyond 170 days, and confirms the jet origin for the observed outflow, in contrast to more slowly declining expectations for “failed-jet” scenarios. We show here that the broadband (radio, optical, X-ray) afterglow is consistent with a structured outflow where an ultra-relativistic jet, with a Lorentz factor of Γ ≳ 100, forms a narrow core (∼5°) and is surrounded by a wider angular component that extends to ∼15°, which is itself relativistic (Γ ≳ 5). For a two-component model of this structure, the late-time optical decline, where F ∝ t ‑α , is α = 2.20 ± 0.18, and for a Gaussian structure the decline is α = 2.45 ± 0.23. We find the Gaussian model to be consistent with both the early ∼10 days and late ≳290 days data. The agreement of the optical light curve with the evolution of the broadband spectral energy distribution, and its continued decline, indicates that the optical flux is arising primarily from the afterglow and not any underlying host system. This provides the deepest limits on any host stellar cluster with a luminosity ≲4000 L ⊙ (M F606W ≳ ‑4.3).
Item Type: | Journal Article | |||||||||||||||||||||
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Subjects: | Q Science > QB Astronomy | |||||||||||||||||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | |||||||||||||||||||||
Library of Congress Subject Headings (LCSH): | Neutron stars, Gravitational waves | |||||||||||||||||||||
Journal or Publication Title: | The Astrophysical Journal | |||||||||||||||||||||
Publisher: | Institute of Physics Publishing, Inc. | |||||||||||||||||||||
ISSN: | 0004-637X | |||||||||||||||||||||
Official Date: | 9 January 2019 | |||||||||||||||||||||
Dates: |
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Volume: | 870 | |||||||||||||||||||||
Number: | 2 | |||||||||||||||||||||
Article Number: | L15 | |||||||||||||||||||||
DOI: | 10.3847/2041-8213/aaf96b | |||||||||||||||||||||
Status: | Peer Reviewed | |||||||||||||||||||||
Publication Status: | Published | |||||||||||||||||||||
Access rights to Published version: | Restricted or Subscription Access | |||||||||||||||||||||
Date of first compliant deposit: | 19 February 2019 | |||||||||||||||||||||
Date of first compliant Open Access: | 20 February 2019 | |||||||||||||||||||||
Grant number: | STFC ST / P000495 / 1 | |||||||||||||||||||||
RIOXX Funder/Project Grant: |
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