The radio afterglow of Swift J1644+57 reveals a powerful jet with fast core and slow sheath

Understand

We model the non-thermal transient Swift J1644+57 as resulting from a relativistic jet powered by the accretion of a tidally-disrupted star onto a super-massive black hole.

• Accompanying synchrotron radio emission is produced by the shock interaction between the jet and the dense circumnuclear medium, similar to a gamma-ray burst afterglow.
• An open mystery, however, is the origin of the late-time radio rebrightening, which occurred well after the peak of the jetted X-ray emission.
• Here, we systematically explore several proposed explanations for this behavior by means of multi-dimensional hydrodynamic simulations coupled to a self-consistent radiative transfer calculation of the synchrotron emission.