Nonthermal afterglow of the binary neutron star merger GW170817: A more natural modeling of electron energy distribution leads to a qualitatively different new solution

Observed properties of the nonthermal afterglow emission of GW170817 from radio to X‐ray are consistent with synchrotron radiation by electrons accelerated in the shock generated by outflow from the merger. However, previous studies modeling these data made a simplified assumption that all electrons in the shock are accelerated as a nonthermal population. Here, we present a new modeling with a more natural electron energy distribution, in which the number fraction f of electrons injected into particle acceleration is variable. Using two models (structured jet and radially stratified spherical outflow) for the outflow geometry, model parameters are determined by fit to the observed data. Interestingly, new solutions are found with radio flux in the regime of low‐frequency tail below ν m in the early phase, where ν m is the frequency corresponding to the lowest electron energy, in contrast to previous studies that found the radio frequency always above ν m . We encourage researchers to take densely sampled low‐frequency radio data in the early phase for future binary neutron star merger events, which would detect ν m passage and give a strong constraint on electron energy distribution and particle acceleration efficiency.