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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

R. ChornockAstrophysical Institute, Department of Physics and Astronomy, 251B Clippinger Lab, Ohio University, Athens, OH 45701, USA; [email protected]E. BergerHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAD. KasenDepartments of Physics and Astronomy, and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720-7300, USAP. S. CowperthwaiteDepartment of Physics, Brandeis University, Waltham, MA 02454, USAM. NichollHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAV. A. VillarHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAK. D. AlexanderHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAP. K. BlanchardHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAT. EftekhariHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAW. FongCenter for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USAR. MarguttiCenter for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USAP. K. G. WilliamsHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAJ. AnnisFermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510, USAD. BroutDepartment of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USAD. A. BrownDepartment of Physics, Syracuse University, Syracuse NY 13224, USAH.-Y. ChenDepartment of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USAM. R. DroutCarnegie ObservatoriesB. FarrDepartment of Physics, University of Oregon, Eugene, OR 97403, USAR. J. FoleyDepartment of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USAJ. A. FriemanFermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510, USAC. L. FryerCenter for Theoretical Astrophysics, Los Alamos National Laboratory, Los Alamos, NM 87544, USAK. HernerFermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510, USAD. E. HolzEnrico Fermi Institute, Department of Physics, Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USAR. KesslerKavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USAT. MathesonNational Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USAB. D. MetzgerDepartment of Physics and Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USAE. QuataertDepartment of Astronomy & Theoretical Astrophysics Center, University of California, Berkeley, CA 94720-3411, USAA. RestDepartment of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USAM. SakoDepartment of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USAD. M. ScolnicKavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USAN. SmithSteward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USAM. Soares-SantosDepartment of Physics, Brandeis University, Waltham, MA 02454, USA

2017en

ABI

Annotatsiya

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 μ m. Our fiducial model with 0.04 M ⊙ of ejecta, an ejection velocity of v = 0.1 c , and a lanthanide concentration of X lan = 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.

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DOI: 10.3847/2041-8213/aa905c

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