Gamma-ray burst afterglow light curves from realistic density profiles

Radio Afterglow of the Jetted Tidal Disruption Event Swift J1644+57

Radio Afterglow of the Jetted Tidal Disruption Event Swift J1644+57

On the existence of a reverse shock in magnetized GRB ejecta

The role of magnetic fields in gamma-ray burst (GRB) flows remains controversial. The study of the early afterglow phases and, in particular, of the reverse shock dynamics and associated emission offers a promising probe of the magnetization of the ejecta. In this paper, we derive the conditions for the existence of a reverse shock in arbitrarily magnetized ejecta that decelerate and interact with the circumburst medium. Both constant and wind-like density profiles are considered. We show, in contrast to previous estimates, that ejecta with magnetization larger than unity are not crossed by a reverse shock for a large fraction of the parameter space relevant to GRB flows. Allowing for shell…