Dynamics of Relativistic Shock Waves Subject to a Strong Radiation Drag: Similarity Solutions and Numerical Simulations

We examine the effect of Compton drag on the dynamics of a relativistic shock wave. Similarity solutions describing a radiation-supported shock are obtained for certain profiles of the external radiation intensity and the density of the unshocked ejecta, and are compared with 1D numerical simulations of a blast wave expanding into an ambient medium containing isotropic seed radiation. Both the analytic model and the simulations indicate that under realistic conditions the radiation drag should strongly affect the dynamics and structure of the shocked layer. In particular, our calculations show significant strengthening of the reverse shock and weakening of the forward shock over time of the order of the inverse Compton cooling time. We conclude that the effect of radiation drag on the evolution of the emitting plasma should affect the resultant light curves and, conceivably, spectra of the observed emission during strong blazar flares.