Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source D. A. Coulter1, R. J. Foley1, C. D. Kilpatrick1, M. R. Drout2, A. L. Piro2, B. J. Shappee2;3, M. R. Siebert1, J. D. Simon2, N. Ulloa4, D. Kasen5;6, B. F. Madore2;7, A. Murguia-Berthier1, Y.-C. Pan1, J. X. Prochaska1, E. Ramirez-Ruiz1;8, A. Rest9;10, C. Rojas-Bravo1 1Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA 2The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 3 Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA 4Departamento de F´ısica y Astronom´ıa, Universidad de La Serena, La Serena, Chile 5Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 6Departments of Physics and Astronomy, University of California, Berkeley, CA 94720, USA ucDepartment of Astronomy and Astrophysics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 8Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark 9Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 10Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles arXiv:1710.05452v1 [astro-ph.HE] 16 Oct 2017 Street, Baltimore, MD 21218, USA ∗To whom correspondence should be addressed; E-mail:
[email protected]. On 2017 August 17, the Laser Interferometer Gravitational-wave Observa- tory (LIGO) and the Virgo interferometer detected gravitational waves em- anating from a binary neutron star merger, GW170817. Nearly simultane- ously, the Fermi and INTEGRAL telescopes detected a gamma-ray transient, GRB 170817A.