Relativistic Shear Flows and the Gamma-Ray Emission of GW170817*

We present an analysis of the radiation characteristics of kinetic shear boundary layers created by relativistic

plasma jets interacting with the ambient medium.  Using the electromagnetic field output of particle-in-cell (PIC) simulations,  we solve the motion of a large number of test electrons and compute their radiated power and peak frequency.  By summing over the radiation output of all highly radiative electrons, we obtain the distribution of the total radiated energy and characteristic frequency as functions of the view angle relative to the bulk flow.  This result has important implications for the observed radiation output of short gamma-ray bursts viewed at large angles from the jet axis, such as the neutron star merger event GW170817/GRB170817A.