Poynting flux transport channels formed in polar cap regions of neutron star magnetospheres
arXiv:2405.20866 · doi:10.1051/0004-6361/202450949
Abstract
Pair cascades in polar cap regions of neutron stars are considered to be an essential process in various models of coherent radio emissions of pulsars. The cascades produce pair plasma bunch discharges in quasi-periodic spark events. The cascade properties, and therefore also the coherent radiation, depend strongly on the magnetospheric plasma properties and vary significantly across and along the polar cap. Importantly, where the radio emission emanates from in the polar cap region is still uncertain. We investigate the generation of electromagnetic waves by pair cascades and their propagation in the polar cap for three representative inclination angles of a magnetic dipole, , , and . We use two-dimensional particle-in-cell simulations that include quantum-electrodynamic pair cascades in a charge-limited flow from the star surface. We find that the discharge properties are strongly dependent on the magnetospheric current profile in the polar cap and that transport channels for high intensity Poynting flux are formed along magnetic field lines where the magnetospheric currents approach zero and where the plasma cannot carry the magnetospheric currents. There, the parallel Poynting flux component is efficiently transported away from the star and may eventually escape the magnetosphere as coherent radio waves. The Poynting flux decreases with increasing distance from the star in regions of high magnetospheric currents. Our model shows that no process of energy conversion from particles to waves is necessary for the coherent radio wave emission. Moreover, the pulsar radio beam does not have a cone structure; rather, the radiation generated by the oscillating electric gap fields directly escapes along open magnetic field lines in which no pair creation occurs.
18 pages, 11 figures, 2 tables
References in corpus (17)
- Radiation Reaction Effects on Radiation Pressure Acceleration
- 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
- Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations
- Polar-cap accelerator and radio emission from pulsars
- Pulsar radio emission mechanisms: a critique
- Differential Frequency-dependent Delay from the Pulsar Magnetosphere
- Radio Emission and Electric Gaps in Pulsar Magnetospheres
- Pulsar gamma-ray emission in the radiation reaction regime
- Kinetic model of large-amplitude oscillations in neutron star pair cascades
- Internal heating mechanisms in neutron stars
- Particle acceleration and radiation reaction in a strongly magnetized rotating dipole
- Linear acceleration emission of pulsar relativistic streaming instability and interacting plasma bunches
- Polarized QED Cascades over Pulsar Polar Caps
- Particle-in-cell simulations of electron-positron cyclotron maser forming pulsar radio zebras
- Particle motion in neutron stars ultra-strong electromagnetic field: the influence of radiation reaction
- Frequency resolved radio and high-energy emission of pulsars
- Streaming instability in neutron star magnetospheres: No indication of soliton-like waves