The polar-cap accelerator and radio emission from pulsars

A key parameter of the polar-cap accelerator is a = j/cρGJ, where j is the electric current and ρGJ is the corotation charge density. The customary model assumed a = 1 ± ǫ and found ǫ ≪ 1, steady acceleration of particles, and e creation. The fine-tuning of a to 1 is not, however, favored by the magnetosphere, and the accelerator with |a − 1| > ǫ ∼ 10 is qualitatively different. For 0 < a < 1 − ǫ, a charge-separated outflow forms at a low voltage, and no e pairs are created. For a > 1 + ǫ, the accelerator is unstable and a high voltage is generated by electrostatic and induction effects. We argue that the pulsar activity is generated by an unsteady gap near the surface that forms if a > 1 or a < 0. The unsteady voltage implies unsteady rotation of the open magnetic tube and generation of Alfven waves, which are ducted along the tube. Their energy flux can directly feed radio emission as Alfven waves convert to electromagnetic waves. Subject headings: plasmas — stars: magnetic fields, neutron