Externally-driven plasma models as candidates for pulsar radio emission

Abstract

Coherent radio emission from pulsars originates from excited plasma waves in an ultra-relativistic and strongly magnetized electron-positron pair plasma streaming along the open magnetic field lines of the pulsar. Traditional coherent radio emission models have relied on instabilities in this pair plasma. Recently alternative models have been suggested. These models appeal to direct coupling of the external electromagnetic field to the superluminal O-mode ($l{t}_2$ mode) during the time-dependent pair cascade process at the polar gap. The objective of this work is to provide generic constraints on plasma models based on $l{t}_2$ mode using realistic pulsar parameters. We find that the very short timescale associated with pair cascades does not allow $l{t}_2$ mode to be excited at radio frequencies and the impulsive energy transfer can only increase the kinetic spread ("temperature") of the pair plasma particles. Moreover, under homogeneous plasma conditions, plasma waves on both branches of O-mode (i.e. superluminal $l{t}_2$ and subluminal $l{t}_1$) cannot escape the plasma. In the strongly magnetized pair plasma, only the extraordinary mode ($t$ mode) can escape freely. We show that any generic fictitious mechanisms does not result in the wave electric field of $t$ mode to have predominant orientation either parallel or perpendicular to the magnetic field plane as observed. Such fictitious mechanisms will inevitably lead to depolarization of signals and cannot account for the highly polarized single pulses observed in pulsars. We suggest coherent curvature radiation as a promising candidate for pulsar radio emission mechanism.

Accepted for publication in MNRAS

References in corpus (14)

• A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation
• Time-dependent pair cascades in magnetospheres of neutron stars I. Dynamics of the polar cap cascade with no particle supply from the neutron star surface
• Profile and polarization characteristics of energetic pulsars
• Unraveling the nature of coherent pulsar radio emission
• Two Modes of Partially Screened Gap
• The Nature of Coherent Radio Emission from Pulsars
• On the adiabatic walking of plasma waves in a pulsar magnetosphere
• A Mechanism of Spark Motion in Inner Acceleration Region to Investigate Subpulse Drifting in Pulsars
• A Single spark model for PSR J2144$-$3933
• Joint radio and X-ray modelling of PSR~J1136+1551
• XMM-Newton observation of the nearby pulsar B1133+16
• Toward an Empirical Theory of Pulsar Emission XI. Understanding the Orientations of Pulsar Radiation and Supernova "Kicks"
• Magnetothermal Evolution of Neutron Stars with Emphasis to Radio Pulsars
• Coherent emission from QED cascades in pulsar polar caps