Subsequent Non-thermal Emission due to the Kilonova Ejecta in GW170817

Abstract

The ejected material at the binary neutron star merger GW170817 was confirmed as a kilonova by UV, optical and IR observations. This event provides a unique opportunity to investigate the particle acceleration at a mildly relativistic shock propagating in the circum binary medium. In this {\it Letter}, we simulate the non-thermal emission from electrons accelerated by the shock induced by the kilonova ejecta with a time-dependent method. The initial velocity and mass of the ejecta in the simulations are obtained from the kilonova observations in GW170817. If the ambient density is high enough (\(\geq 10^{-2}~\mbox{cm}^{-3}\)), radio, optical/IR, and X-ray signals will be detected in a few years, though the off-axis short gamma-ray burst models, accounting for the X-ray counterpart detected at \(\sim 10\) days after the merger, implies low ambient density. Even for low ambient density as \(\sim 10^{-3}~\mbox{cm}^{-3}\), depending on the microscopic parameters for the electron acceleration, we can expect a growth of radio flux as \(\sim \mu\)Jy in a few years.