| Abstract
| - We show that a jet in an active galactic nucleus (AGN) is produced by a rotating massive black hole. The jet contains relativistic protons accelerated by the corotating radial magnetic field, which is brought to the black hole horizon by the accreting disc matter. The Lorentz factor of protons at the light cylinder surface can gain a value of γ as high as ≃ 105. The main proton energy is in the azimuthal rotation, and only a small part is in the radial motion. The jet matter, flowing out slowly behind the light cylinder, vr=cγ−1/2, is accelerated moving in the expanding poloidal magnetic field (magnetic nozzle) and it obtains a longitudinal Lorentz factor of Γ ≃ (B/BL)−1/2 ≤ 10 (where BL is the value of the magnetic field at the light cylinder surface, BL ≃ 102 G). The observed short time variability from some AGNs, τ ≃ 300 s, can be explained by the excitation of the collective ion plasma waves near the jet base.
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