The Emergence of a Lanthanide-rich Kilonova Following the Merger of Two Neutron Stars
Wollaeger, R. T.; Fryer, C. L.; Korobkin, O.; Covino, S.; D'Avanzo, P.; Fontes, C. J.; Melandri, A.; Pian, E.; D'Elia, V.; Palazzi, E.; Greiner, J.; Lyman, J. D.; Ulaczyk, K.; Fruchter, A. S.; Wijers, R. A. M. J.; Rol, E.; Milvang-Jensen, B.; Watson, D.; Fynbo, J. P. U.; Kann, D. A.; O'Brien, P. T.; Rowlinson, A.; Perley, D. A.; Wiersema, K.; Steeghs, D.; Osborne, J. P.; Levan, A. J.; Rabus, M.; Tanvir, N. R.; Malesani, D.; Cano, Z.; Evans, P. A.; Hjorth, J.; Jakobsson, P.; Thöne, C. C.; Jørgensen, U. G.; de Ugarte Postigo, A.; Irwin, M. J.; Gompertz, B. P.; Piranomonte, S.; Schulze, S.; Figuera Jaimes, R.; McMahon, R. G.; Copperwheat, C. M.; González-Fernández, C.; Mandel, I.; Rosswog, S.; Fairhurst, S.; Kangas, T.; Hodosan, G.; Fujii, Y. I.; Sutton, P.; Rosetti, S.; Even, W. P.
United Kingdom, United States, Sweden, Denmark, Italy, Spain, Japan, Germany, Iceland, Chile, Australia, Netherlands, Israel
Abstract
We report the discovery and monitoring of the near-infrared counterpart (AT2017gfo) of a binary neutron-star merger event detected as a gravitational wave source by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo (GW170817) and as a short gamma-ray burst by Fermi Gamma-ray Burst Monitor (GBM) and Integral SPI-ACS (GRB 170817A). The evolution of the transient light is consistent with predictions for the behavior of a “kilonova/macronova” powered by the radioactive decay of massive neutron-rich nuclides created via r-process nucleosynthesis in the neutron-star ejecta. In particular, evidence for this scenario is found from broad features seen in Hubble Space Telescope infrared spectroscopy, similar to those predicted for lanthanide-dominated ejecta, and the much slower evolution in the near-infrared {K}{{s}}-band compared to the optical. This indicates that the late-time light is dominated by high-opacity lanthanide-rich ejecta, suggesting nucleosynthesis to the third r-process peak (atomic masses A≈ 195). This discovery confirms that neutron-star mergers produce kilo-/macronovae and that they are at least a major—if not the dominant—site of rapid neutron capture nucleosynthesis in the universe.