Toward an Empirical Theory of Pulsar Emission. X. On the Precursor and
  Postcursor Emission
  Precursors and postcursors (PPCs) are rare emission components detected in a
handful of pulsars that appear beyond the main pulse emission, in some cases
far away from it. In this paper we attempt to characterize the PPC emission in
relation to the pulsar main pulse geometry. In our analysis we find that PPC
components have properties very different from that of outer conal emission.
The separation of the PPC components from the main pulse center remains
constant with frequency. In addition the beam opening angles corresponding to
the separation of PPC components from the pulsar center are much larger than
the largest encountered in conal emission. Pulsar radio emission is believed to
originate within the magnetic polar flux tubes due to the growth of
instabilities in the outflowing relativistic plasma. Observationally, there is
strong evidence that the main pulse emission originates at altitudes of about
50 neutron star radii for a canonical pulsar. Currently, the most plausible
radio emission model that can explain main pulse emission is the coherent
curvature radiation mechanism, wherein relativistic charged solitons are formed
in a non-stationary electron-positron-pair plasma. The wider beam opening
angles of PPC require the emission to emanate from larger altitudes as compared
to the main pulse, if both these components originate by the same emission
mechanism. We explore this possibility and find that this emission mechanism is
probably inapplicable at the height of the PPC emission. We propose that the
PPC emission represents a new type of radiation from pulsars with a mechanism
different from that of the main pulse.
