Electromagnetic transients from radioactive decays accompanying short gamma-ray bursts

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The final inspiral stages and the subsequent coalescence of two neutron stars or of a neutron star and a stellar-mass black hole are the prime gravitational wave sources in the kilohertz regime. Moreover, they are thought to be the "central engines" behind the (short) Gamma-ray burst phenomenon. During the merging process, gravitational torques launch decompressed neutron star matter into unbound or nearly unbound, eccentric orbits. This debris consists of radioactive nuclei that finally decay into so-called r-process ("rapid neutron capture") elements and this decay must produce an isotropic, bright, but rapidly decaying electromagnetic transient. The identification of such transients is crucial since it increases the effective sensitivity of ground-based gravitational wave detector facilities and it places compact binary mergers in an astrophysical context by providing information on the host galaxy, the local environment and on binary star properties and evolution. Thus, current and future transient surveys can constrain the still unknown origin of the heaviest elements in the Universe. The aim of this proposal is to overcome the latter restriction and to perform a complete calculation from the initial merger process over the evolution of the debris material (including feedback from nuclear energy release onto the hydrodynamics) to the final light curves.