The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. II. UV, Optical, and Near-IR Light Curves and Comparison to Kilonova Models

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  • LIGO Scientific Collaboration
  • P. S. Cowperthwaite
  • E. Berger
  • V. A. Villar
  • B. D. Metzger
  • M. Nicholl
  • R. Chornock
  • P. K. Blanchard
  • W. Fong
  • R. Margutti
  • M. Soares-Santos
  • K. D. Alexander
  • S. Allam
  • J. Annis
  • D. Brout
  • D. A. Brown
  • R. E. Butler
  • H. -Y. Chen
  • H. T. Diehl
  • Z. Doctor
  • M. R. Drout
  • T. Eftekhari
  • B. Farr
  • D. A. Finley
  • R. J. Foley
  • J. A. Frieman
  • C. L. Fryer
  • J. García-Bellido
  • M. S. S. Gill
  • J. Guillochon
  • K. Herner
  • D. E. Holz
  • D. Kasen
  • R. Kessler
  • J. Marriner
  • T. Matheson
  • Jr E. H. Neilsen
  • E. Quataert
  • A. Palmese
  • A. Rest
  • M. Sako
  • D. M. Scolnic
  • N. Smith
  • D. L. Tucker
  • P. K. G. Williams
  • E. Balbinot
  • J. L. Carlin
  • E. R. Cook
  • F. Durret
  • T. S. Li
  • P. A. A. Lopes

Colleges, School and Institutes


We present UV, optical, and NIR photometry of the first electromagnetic counterpart to a gravitational wave source from Advanced LIGO/Virgo, the binary neutron star merger GW170817. Our data set extends from the discovery of the optical counterpart at $0.47$ days to $18.5$ days post-merger, and includes observations with the Dark Energy Camera (DECam), Gemini-South/FLAMINGOS-2 (GS/F2), and the {\it Hubble Space Telescope} ({\it HST}). The spectral energy distribution (SED) inferred from this photometry at $0.6$ days is well described by a blackbody model with $T\approx 8300$ K, a radius of $R\approx 4.5\times 10^{14}$ cm (corresponding to an expansion velocity of $v\approx 0.3c$), and a bolometric luminosity of $L_{\rm bol}\approx 5\times10^{41}$ erg s$^{-1}$. At $1.5$ days we find a multi-component SED across the optical and NIR, and subsequently we observe rapid fading in the UV and blue optical bands and significant reddening of the optical/NIR colors. Modeling the entire data set we find that models with heating from radioactive decay of $^{56}$Ni, or those with only a single component of opacity from $r$-process elements, fail to capture the rapid optical decline and red optical/NIR colors. Instead, models with two components consistent with lanthanide-poor and lanthanide-rich ejecta provide a good fit to the data, the resulting "blue" component has $M_\mathrm{ej}^\mathrm{blue}\approx 0.01$ M$_\odot$ and $v_\mathrm{ej}^\mathrm{blue}\approx 0.3$c, and the "red" component has $M_\mathrm{ej}^\mathrm{red}\approx 0.04$ M$_\odot$ and $v_\mathrm{ej}^\mathrm{red}\approx 0.1$c. These ejecta masses are broadly consistent with the estimated $r$-process production rate required to explain the Milky Way $r$-process abundances, providing the first evidence that BNS mergers can be a dominant site of $r$-process enrichment.

Bibliographic note

13 Pages, 3 Figures, 2 Tables. ApJL, In Press. Keywords: GW170817, LVC


Original languageEnglish
Article numberL17
Number of pages10
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 16 Oct 2017


  • astro-ph.HE