On the adiabatic walking of plasma waves in a pulsar magnetosphere

The pulsar radio emission is generated in the near magnetosphere of the neutron star and it has to propagate through the rest of it to emerge into the interstellar medium. An important issue is whether this propagation affects the planes of polarization of the generated radiation. Observationally, there is a sufficient evidence that the emerging radiation is polarized parallel or perpendicular to the magnetic field line planes that should be associated with the ordinary O and extraordinary X plasma modes respectively, excited by some radiative process. This strongly suggests that the excited X- and O-modes are not affected by the so-called Adiabatic Walking that causes a slow rotation of polarization vectors. In this paper we demonstrate that the conditions for the Adiabatic Walking are not fulfilled within the soliton model of pulsar radio emission, in which the coherent curvature radiation occurs at frequencies much lower than the characteristic plasma frequency. The X-mode propagates freely and observationally represents the primary polarization mode. The O-mode has difficulties in escaping from the pulsar plasma, nonetheless it is sporadically observed as a weaker secondary polarization mode. We discuss a possible scenario under which the O-mode can also escape from the plasma and reach an observer.