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Science. 2017 Dec 22;358(6370):1574-1578. doi: 10.1126/science.aaq0186. Epub 2017 Oct 16.

Early spectra of the gravitational wave source GW170817: Evolution of a neutron star merger.

Author information

1
The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA. shappee@hawaii.edu.
2
Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA.
3
The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA.
4
Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile.
5
Núcleo de Astronomía de la Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Avenida Ejército 441, Santiago, Chile.
6
Millennium Institute of Astrophysics, Santiago, Chile.
7
Departments of Physics and Astronomy, 366 LeConte Hall, University of California---Berkeley, Berkeley, CA 94720, USA.
8
Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
9
Department of Astronomy and Astrophysics, University of California-Santa Cruz, Santa Cruz, CA 95064, USA.
10
Dark Cosmology Center, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark.
11
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA.
12
Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.
13
Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA.
14
Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
15
Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, C.P. 58190, Morelia, Mexico.
16
University of Victoria, Victoria, BC V8P 5C2, Canada.
17
National Research Council (NRC) Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada.
18
Instituto de Física y Astronomía, Universidad de Valparaíso, Valparaíso, Chile.
19
George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy and Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA.
20
Department of Physics and Joint Institute for Nuclear Astrophysics (JINA) Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556, USA.
21
Sydney Institute for Astronomy, School of Physics, A28, University of Sydney, NSW 2006, Australia.

Abstract

On 17 August 2017, Swope Supernova Survey 2017a (SSS17a) was discovered as the optical counterpart of the binary neutron star gravitational wave event GW170817. We report time-series spectroscopy of SSS17a from 11.75 hours until 8.5 days after the merger. Over the first hour of observations, the ejecta rapidly expanded and cooled. Applying blackbody fits to the spectra, we measured the photosphere cooling from [Formula: see text] to [Formula: see text] kelvin, and determined a photospheric velocity of roughly 30% of the speed of light. The spectra of SSS17a began displaying broad features after 1.46 days and evolved qualitatively over each subsequent day, with distinct blue (early-time) and red (late-time) components. The late-time component is consistent with theoretical models of r-process-enriched neutron star ejecta, whereas the blue component requires high-velocity, lanthanide-free material.

PMID:
29038374
DOI:
10.1126/science.aaq0186

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