There are no physical principles disallowing the existence of extended sources of the electromagnetic field which move faster than light in empty space (Bolotovskii and Ginzburg 1972). Charge-current distributions whose patterns rotate around a fixed axis rigidly, and so have a phase speed that is greater than the speed of light in vacuo outside the light cylinder, emit radiation—different from both Cherenkov and synchrotron radiation—which has the following characteristics:

1. 1. It arises almost exclusively from the vicinity of those points within the source which, at the emission time, approach the observer with the speed of light and with zero acceleration.

2. 2. It consists of the superposition of a (continuous) set of narrow radiation beams whose flux densities fall off with the radial distance R from the source like R–1 (rather than R–2), and so it is intrinsically coherent.

3. 3. It has a power-law spectrum with no exponential cut-off, at high harmonics of the rotation frequency, whose index lies between –1 and –3 if the longitudinal distribution of the source density is pulse-like.

4. 4. It consists of two concurrent elliptically polarized signals whose position angles are predominantly orthogonal and simultaneously vary in direction in the course of each rotation.

I suggest that this radiation, here referred to as Schott radiation (cf. Schott 1912), may in fact be that received from pulsars.