Toward explanation of microstructure in pulsar radio emission

Propagation of relativistically beamed radio photons through the ultrarelativistic highly magnetized plasma of pulsar magnetosphere is considered. The photons are found to be subject to an additional strong focusing inside the beam because of induced Compton scattering off the plasma particles. Incorporating this focusing effect is shown to improve on the angular beaming model of pulsar microstructure. For the typical conditions in the scattering region, the photon beam appears up to a few hundred times squeezed and its size becomes compatible with the observed micropulse widths. The induced Compton scattering can also account for the polarization properties of micropulses. Furthermore, given a favourable observational geometry, the focusing effect can explain the giant micropulses observed in the Vela and some other pulsars.