Early Gamma‐Ray Burst Afterglows from Relativistic Blast Waves in General Radiative Regimes

We present simple analytical expressions for the predicted spectral and temporal behavior of the early afterglow radiation from gamma-ray bursts in radiative regimes intermediate between the adiabatic and the fully radiative solutions of the blast-wave hydrodynamic equations. Our expressions are valid as long as the relativistic electrons responsible for the observed synchrotron emission are in the fast-cooling regime and the blast wave is relativistic. We show that even a slight deviation from a perfectly adiabatic evolution results in significant changes of the temporal characteristics of the afterglow emission.