Shock within a shock: revisiting the radio flares of NS merger ejecta and GRB-supernovae

Understand

Fast ejecta expelled in binary neutron star (NS) mergers or energetic supernovae (SNe) should produce late-time synchrotron radio emission as the ejecta shocks into the surrounding ambient medium.

• Models for such radio flares typically assume the ejecta expands into an unperturbed interstellar medium (ISM).
• However, it is also well-known that binary NS mergers and broad-lined Ic SNe can harbor relativistic jetted outflows.
• In this work, we show that such jets shock the ambient ISM ahead of the ejecta, thus evacuating the medium into which the ejecta subsequently collides.