  Observational data imply the presence of superluminal electric currents in
pulsar magnetospheres. Such sources are not inconsistent with special
relativity; they have already been created in the laboratory. Here we describe
the distinctive features of the radiation beam that is generated by a rotating
superluminal source and show that (i) it consists of subbeams that are narrower
the farther the observer is from the source: subbeams whose intensities decay
as 1/R instead of 1/R^2 with distance (R), (ii) the fields of its subbeams are
characterized by three concurrent polarization modes: two modes that are
'orthogonal' and a third mode whose position angle swings across the subbeam
bridging those of the other two, (iii) its overall beam consists of an
incoherent superposition of such coherent subbeams and has an intensity profile
that reflects the azimuthal distribution of the contributing part of the source
(the part of the source that approaches the observer with the speed of light
and zero acceleration), (iv) its spectrum (the superluminal counterpart of
synchrotron spectrum) is broader than that of any other known emission and
entails oscillations whose spacings and amplitudes respectively increase and
decrease algebraically with increasing frequency, and (v) the degree of its
mean polarization and the fraction of its linear polarization both increase
with frequency beyond the frequency for which the observer falls within the
Fresnel zone. We also compare these features with those of the radiation
received from the Crab pulsar.
