Radioactively powered electromagnetic counterparts of neutron star mergers

The most promising astrophysical sources of gravitational waves (GWs) for ground-based inter-ferometers such as LIGO and Virgo are the inspiral and merger of binary neutron star (NS) and black hole systems. However, maximizing the scientific benefits of a GW detection will require identifying a coincident electromagnetic counterpart. One of the most likely sources of isotropic emission from NS mergers is a supernova-like transient powered by the radioactive decay of r-process elements synthesized in the merger ejecta. We present the first calculations of the optical transients from NS mergers that self consistently determine the radioactive heating using a nuclear reaction network and which determine the resulting light curve with a Monte Carlo radiation transfer calculation. Due to the rapid evolution and low luminosity of NS merger transients, optical counterpart searches triggered by a GW detection will require close collaboration between the GW and astronomical communities. NS merger transients may also be detectable following a short duration Gamma-Ray Burst or blindly with present or upcoming optical transient surveys.