Speaker
Description
Binary neutron star mergers are expected to produce a relativistic jet and a fast dynamical ejecta, with mildly relativistic velocities extending to $\beta=v/c>0.6$. We consider the radio to X-ray synchrotron emission produced by collisionless shocks driven by such spherical fast ejecta into the interstellar medium. We provide analytic expressions for this non-thermal emission, which are an accurate description (to 10's of percent) of the evolution of the flux, including at the phase of deceleration to sub-relativistic expansion. This is a significant improvement over earlier results, based on extrapolations of results valid for $\gamma\beta\gg1$ or $\ll1$ to $\gamma\beta\approx1$, which overestimate the flux by an order of magnitude for typical parameter values. Our results will enable a more reliable inference of ejecta parameters from future measurements of the non-thermal emission. We will also present initial results regarding the impact of our improved treatment of the emission from mildly relativistic plasmas on the predicted non-thermal radiation driven by non-spherical (jet/cocoon) components observed off-axis/at late times.
