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

TL;DR

This paper investigates precursor and postcursor emissions in pulsars, revealing they differ from main pulse emissions and likely originate from different mechanisms or altitudes, challenging existing models of pulsar radio emission.

Contribution

It characterizes PPC emissions, showing they have distinct properties and likely originate from different mechanisms or altitudes than main pulse emission, suggesting a new radiation process.

Findings

PPC components have constant separation from the main pulse across frequencies.

PPC beam opening angles are larger than those of conal emissions.

The emission mechanism for PPC is probably different from that of the main pulse.

Abstract

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.