Bunching mechanism for coherent curvature radiation in pulsar magnetospheres

The special case of the axisymmetric steady-state magnetosphere of an aligned rotator is reviewed, and the motion along curved field lines of a relativistic electron-positron plasma created in such a magnetosphere is analyzed. The necessary velocity difference between the positrons and electrons is determined and related to the excitation of two-stream instabilities within the light cylinder, charge bunching, and the generation of coherent curvature radiation at microwave frequencies. The results are generalized to oblique-rotator geometries, and effects of forces due to the radiation field on the bunching amplitude are examined. It is found that for the unstable plasma modes considered, the inclusion of interactions with the radiation field can lead to amplification rather than dissipation of bunching.