ESO/A.J. Levan, N.R. Tanvir

On 17th August 2017, a gravitational wave signal lasting for more than 50 seconds was discovered by the Ligo-Virgo Science Collaboration and just 1.7 seconds later a short burst of gamma rays was detected by the Fermi and INTEGRAL satellites. A new optical and infrared source was identified in the galaxy NGC 4993 that was unlike any other transient ever reported. This was AT2017gfo, a kilonova from the merger of two neutron stars, powered by the radioactive decay of r-processed heavy elements. The European Southern Observatory’s telescopes played a central role in the discovery and we have formed ENGRAVE to exploit ESO’s powerful resources, beginning with the O3 LVC observing runs and now moving into the O4 era.