The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South

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Authors

  • R. Chornock
  • E. Berger
  • D. Kasen
  • P. S. Cowperthwaite
  • M. Nicholl
  • And 27 others
  • V. A. Villar
  • K. D. Alexander
  • P. K. Blanchard
  • T. Eftekhari
  • W. Fong
  • R. Margutti
  • P. K. G. Williams
  • J. Annis
  • D. Brout
  • D. A. Brown
  • H. -Y. Chen
  • M. R. Drout
  • Ben Farr
  • R. J. Foley
  • J. A. Frieman
  • C. L. Fryer
  • K. Herner
  • D. E. Holz
  • R. Kessler
  • T. Matheson
  • B. D. Metzger
  • E. Quataert
  • A. Rest
  • M. Sako
  • D. M. Scolnic
  • N. Smith
  • M. Soares-Santos

Colleges, School and Institutes

Abstract

We present a near-infrared spectral sequence of the electromagnetic counterpart to the binary neutron star merger GW170817 detected by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo. Our data set comprises seven epochs of J+H spectra taken with FLAMINGOS-2 on Gemini-South between 1.5 and 10.5 days after the merger. In the initial epoch, the spectrum is dominated by a smooth blue continuum due to a high-velocity, lanthanide-poor blue kilonova component. Starting the following night, all of the subsequent spectra instead show features that are similar to those predicted in model spectra of material with a high concentration of lanthanides, including spectral peaks near 1.07 and 1.55 μm. Our fiducial model with 0.04 M of ejecta, an ejection velocity of v = 0.1c, and a lanthanide concentration of Xlan = 10−2 provides a good match to the spectra taken in the first five days, although it over-predicts the late-time fluxes. We also explore models with multiple fitting components, in each case finding that a significant abundance of lanthanide elements is necessary to match the broad spectral peaks that we observe starting at 2.5 days after the merger. These data provide direct evidence that binary neutron star mergers are significant production sites of even the heaviest r-process elements.

Details

Original languageEnglish
Article numberL19
Number of pages7
JournalAstrophysical Journal Letters
Volume848
Issue number2
Publication statusPublished - 16 Oct 2017

Keywords

  • astro-ph.HE, astro-ph.GA, astro-ph.SR, binaries: close, nuclear reactions, nucleosynthesis, abundances, stars: neutron