Non-Thermal Emission Following Compact Objects Mergers

Mergers of compact objects are expected to produce a highly relativistic collimated ejecta along with a quasi-spherical mildly relativistic ejecta. We model the non-thermal emission produced by the relativistic ejecta. Guided by 1D and 2D numerical calculations (that we carried out using our purposely modified relativistic hydrodynamics AMR code), we derived analytic and semi-analytic formulae describing the signal expected from collisionless shocks driven by the mildly relativistic (\gamma\beta~1) Kilonova ejecta, and by moderately relativistic (\gamma<10) outflow that is likely to dominate the emission from jetted outflows observed off-axis. Our results improve upon earlier order-of-magnitude estimates based on extrapolations of non- or ultra-relativistic results. They are thus essential for inferring constraints on the fast parts of the ejecta based on future radio & X-ray observations. Specifically, we provide an alternative explanation, different from that commonly considered in the literature, for the extensive radio & X-ray data of GW170817. Existing models consider a narrow ultra-relativistic jet and have difficulty accounting for all data. We suggest a wider-angle stratified ejecta with a lower Lorentz factor range. It is the first single-component complete numerical calculation that fits all the radio & X-ray data of this unprecedented event.