Pulsar radio emission mechanism I : On the amplification of Langmuir waves in the linear regime

Abstract

Observations suggest that in normal period radio pulsars, coherent curvature radiation is excited within 10$\%$ of the light cylinder. The coherence is attributed to Langmuir mode instability in a relativistically streaming one-dimensional plasma flow along the open magnetic field lines. In this work, we use a hot plasma treatment to solve the hydrodynamic dispersion relation of Langmuir mode for realistic pulsar parameters. The solution involves three scenarios of two-stream instability viz., driven by high energy beams, due to longitudinal drift that leads to a separation of electron-positron distribution functions in the secondary plasma and due to cloud-cloud interaction causing spatial overlap of two successive secondary plasma clouds. We find that sufficient amplification can be obtained only for the latter two scenarios. Our analysis shows that longitudinal drift is characterized by high growth rates only for certain multi-polar surface field geometry. For these configurations, very high growth rates are obtained starting from a few tens of km from the neutron star surface, which then falls monotonically with increasing distance. For cloud-cloud overlap, growth rates become high starting only after a few hundred km from the surface, which first increases and then decreases with increasing distance. A spatial window of up to around a 1000 km above the neutron star surface has been found where large amplitude Langmuir waves can be excited while the pair plasma is dense enough to account for high brightness temperature.

arXiv commentAccepted for publication in MNRAS

References in corpus (28)

• Pulsar Jets: Implications for Neutron Star Kicks and Initial Spins
• Evidence for alignment of the rotation and velocity vectors in pulsars
• Drifting subpulses and inner acceleration regions in radio pulsars
• Pair-production multiplicities in rotation-powered pulsars
• Profile and polarization characteristics of energetic pulsars
• Toward An Empirical Theory of Pulsar Emission. VII. On the Spectral Behavior of Conal Beam Radii and Emission Heights
• The spark-associated soliton model for pulsar radio emission
• Curvature radiation in pulsar magnetospheric plasma
• Pulsar Spin-Velocity Alignment: Kinematic Ages, Birth Periods and Braking Indices
• On the maximum pair multiplicity of pulsar cascades
• Comparing Geometrical and Delay Radio Emission Heights in Pulsars
• Pair Creation in the Pulsar Magnetosphere
• Pair cascades in the magnetospheres of strongly-magnetized neutron stars
• Vacuum gaps in pulsars and PSR J2144-3933
• Unraveling the nature of coherent pulsar radio emission
• Toward an Empirical Theory of Pulsar Emission. IX. On the Peculiar Properties and Geometric Regularity of Lyne & Manchester's "Partial Cone" Pulsars
• Pulsar Spin--Velocity Alignment: Further Results and Discussion
• Modelling of surface magnetic field in neutron stars: application to radio pulsars
• 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 Single spark model for PSR J2144$-$3933
• Relativistic charge solitons created due to nonlinear Landau damping: A candidate for explaining coherent radio emission in pulsars
• New mechanism of pulsar radio emission
• Evaluating the Evidence of Multipolar Surface Magnetic Field in PSR J0108$-$1431
• Beam Instabilities in Magnetized Pair Plasma
• Excitation of Alfven Waves and Pulsar Radio Emission
• Wave dispersion in pulsar plasma: 3. Beam-driven instabilities