A model for pulsar nullings.

A model explaining the pulsar nulling and phase memory phenomena is developed in the frame of the plasma model for the pulsar radiation developed by the authors during the last few years. According to this model after fulfilment of the resonant conditions the pulsar radio emission is generated in definite places of the magnetosphere. In addition to waves corresponding to the pulsar radiation, very low-frequency drift waves are also generated in the magnetospheric plasma. These waves propagate transversely to the neutron star magnetic field and encircle the region of the open magnetic field lines. These waves change the curvature radius of field lines and can affect the generation of the radio waves. If the frequency of these waves is about the same as that of the star angular velocity the subpulse drift phenomena can be observed. The particles extracted from the stellar surface form the primary beam distribution function. The particles with more energy radiate γ-quanta and produce electron-positron pairs. The positron accelerates toward the stellar surface and heats it and broaden the primary particles distribution function. This process continues until the density of the extracted particles exceeds the Goldreich-Julian density. At this time the negative potential appears screening the electric field and closing the gap. Simultaneously the peak of the primary particle distribution function moves towards the low Lorentz-factors and does not have enough energy to start the process of generation of radio emission. As a result the nulling phenomenon can be observed. Broadening of the primary particle distribution function can occur with different velocities, depending on the initial distribution function. If the typical duration of this process τ is larger than the period P of pulsar rotation (τ〉P) then nulling is observed. If τ