A charged particle in vacuum and stable motion would induce a time-variant but non-radiating electromagnetic field, whose pattern moves at exactly the particle's speed, but in a medium with lower speed of light this solution is no longer valid, and the only legal solution becomes that of a bow shock (Cerenkov Radiation).
This is analogous to supersonic flow. However even in this flow regime we have isentropic compression body, i.e. a disturbance can travel upstream at supersonic speed without causing shockwave, the air would return to original state at infinity behind the body, and none of the body's kinetic would in theory be converted to heat. (Imagine 2 back to back divergent parts of a rocket nozzle that compresses the incoming flow to Mach 1 then expands it back, the outside envelope is a cylinder.)
As an analogy, is such a body possible in a medium? Let's pretend the medium is sparse so the physical size of the body wouldn't cause displacement flow.
