Speaker
Description
Coherent radio waves from pulsars bring information about relativistic extremely-magnetized pair plasmas in neutron star magnetospheres because the waves originate at plasma kinetic scales. Though various radio emission mechanisms have been proposed in the last decades for their interpretation, many lack the inclusion of self-consistent wave--wave and particle--wave interactions, emission power, spectrum, polarization properties, and directivity that are necessary for interpreting the observations. Hence, particle-in-cell kinetic simulations that self-consistently include the necessary effects are an excellent tool for the plasma and radio emission diagnostics.
Most of pulsar radio waves are probably produced by pair cascades in their polar cap regions by quantum-electrodynamic pair cascades. We carried out PIC simulations that included the relativistic and pair creation in polar caps, magnetospheric currents, and curvature radiative losses of plasma particles. We studied a range of magnetic dipole inclination angles and magnetospheric currents to reveal how radio emissions can operate for various structures of pulsar magnetospheres.
We found that the pair creation events produce intensive Poynting flux originating in an electric gap region close to the star surface. The Poynting flux escapes the polar cap along open field lines where the plasma density is low, and the flux may propagate without significant absorption. Our results indicate that no energy conversion process from particles to waves is necessary for the pulsar coherent radio emissions.
The pulsar emission is directly produced by electromagnetic waves that escape the oscillating gap. Moreover, the produced pulsar radio beam does not have a cone structure; instead, the radiation mostly escapes along those open magnetic field lines in which no pair creation occurs.
