Jan Benáček | Evolution and coherent radio emission of pair-plasma bunches in pulsar magnetospheres

Friday 9 Jun 2023, 10:00 → 12:00 Europe/Berlin

SR05 (Villa)

Pulsars are neutron stars that emit coherent radio beams out of their magnetic poles. However, the origin and exact mechanism of their coherent radio emission are still under investigation. I will discuss one of the proposed coherent radio emission mechanisms that exploits plasma bunches/clouds of electron-positron pairs created during spark events in gap regions. To study the bunch evolution, we utilized particle-in-cell simulations of relativistically hot bunches to investigate the bunch's nonlinear evolution and radiation by linear acceleration emission. We found that the main parameter influencing the bunch evolution is the initial drift velocity between electrons and positrons. For zero drift, the bunches can freely expand, and adjacent bunches may overlap in the phase space and form relativistic streaming instability. Otherwise, the bunches are constrained from expansion and form strong oscillating electrostatic fields. Plasma particles oscillate in these fields and emit coherent radio waves. Furthermore, we found that the bunches constrained from expansion have similar observational characteristics as those observed for pulsars. Their spectrum contains a flat part for low frequencies and power-law profiles for higher frequencies. Also, the emitted radiation is relativistically beamed along the pulsar dipole axis and oscillates at microsecond scales.