Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

Charles D. Kilpatrick, Ryan J. Foley, Daniel Kasen, Ariadna Murguia-Berthier, Enrico Ramirez-Ruiz, David A. Coulter, Maria R. Drout, Anthony L. Piro, Benjamin J. Shappee, Konstantina Boutsia, Carlos Contreras, Francesco Di Mille, Barry F. Madore, Nidia Morrell, Yen-Chen Pan, J. Xavier Prochaska, Armin Rest, César Rojas-Bravo, Matthew R. Siebert, Joshua D. Simon, Natalie Ulloa

Published 2017-10-16Version 1

11 hours after the detection of gravitational wave source GW170817 by the Laser Interferometer Gravitational-Wave Observatory and Virgo Interferometers, an associated optical transient SSS17a was discovered in the galaxy NGC 4993. While the gravitational wave data indicate GW170817 is consistent with the merger of two compact objects, the electromagnetic observations provide independent constraints of the nature of that system. Here we synthesize all optical and near-infrared photometry and spectroscopy of SSS17a collected by the One-Meter Two-Hemisphere collaboration. We find that SSS17a is unlike other known transients. The source is best described by theoretical models of a kilonova consisting of radioactive elements produced by rapid neutron capture (the r-process). We find that SSS17a was the result of a binary neutron star merger, reinforcing the gravitational wave result.