# The Emergence of a Lanthanide-rich Kilonova Following the Merger of Two Neutron Stars

Tanvir, NR and Levan, AJ and Gonzalez-Fernandez, C and Korobkin, O and Mandel, I and Rosswog, S and Hjorth, J and D'Avanzo, P and Fruchter, AS and Fryer, CL and Kangas, T and Milvang-Jensen, B and Rosetti, S and Steeghs, D and Wollaeger, RT and Cano, Z and Copperwheat, CM and Covino, S and D'Elia, V and de Ugarte Postigo, A and Evans, PA and Even, WP and Fairhurst, S and Jaimes, RF and Fontes, CJ and Fujii, YI and Fynbo, JPU and Gompertz, BP and Greiner, J and Hodosan, G and Irwin, MJ and Jakobsson, P and Jorgensen, UG and Kann, DA and Lyman, JD and Malesani, D and McMahon, RG and Melandri, A and O'Brien, PT and Osborne, JP and Palazzi, E and Perley, DA and Pian, E and Piranomonte, S and Rabus, M and Rol, E and Rowlinson, A and Schulze, S and Sutton, P and Thone, CC and Ulaczyk, K and Watson, D and Wiersema, K and Wijers, RAMJ (2017) The Emergence of a Lanthanide-rich Kilonova Following the Merger of Two Neutron Stars. Astrophysical Journal Letters, 848 (2). ISSN 2041-8205

 Preview
Text
The Emergence of a Lanthanide-rich Kilonova Following the Merger of Two Neutron Stars.pdf - Published Version

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 ${K}_{{\rm{s}}}$-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 $A\approx 195$). 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.