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Precursors and postcursors (PPCs) are rare emission components detected in ahandful of pulsars that appear beyond the main pulse emission, in some casesfar away from it. In this paper we attempt to characterize the PPC emission inrelation to the pulsar main pulse geometry. In our analysis we find that PPCcomponents have properties very different from that of outer conal emission.The separation of the PPC components from the main pulse center remainsconstant with frequency. In addition the beam opening angles corresponding tothe separation of PPC components from the pulsar center are much larger thanthe largest encountered in conal emission. Pulsar radio emission is believed tooriginate within the magnetic polar flux tubes due to the growth ofinstabilities in the outflowing relativistic plasma. Observationally, there isstrong evidence that the main pulse emission originates at altitudes of about50 neutron star radii for a canonical pulsar. Currently, the most plausibleradio emission model that can explain main pulse emission is the coherentcurvature radiation mechanism, wherein relativistic charged solitons are formedin a non-stationary electron-positron-pair plasma. The wider beam openingangles of PPC require the emission to emanate from larger altitudes as comparedto the main pulse, if both these components originate by the same emissionmechanism. We explore this possibility and find that this emission mechanism isprobably inapplicable at the height of the PPC emission. We propose that thePPC emission represents a new type of radiation from pulsars with a mechanismdifferent from that of the main pulse.

Toward an Empirical Theory of Pulsar Emission. X. On the Precursor and Postcursor Emission