Magnetocentrifugal acceleration of bulk motion of plasma in pulsar magnetosphere

Abstract

Acceleration of bulk motion of plasma due to magneto centrifugal mechanism is investigated for different shapes of the field lines of 3-D magnetic field. It is shown that this mechanism can be efficient provided that the field line is twisted into direction of rotation. According to the last results of the numerical modelling a fraction of the field lines with such geometrical shape apparently exist in the pulsar magnetosphere close to the last closed field line. In this case the Lorentz factor $\gamma$ increases with the radius $r$ along these field lines as $\gamma\sim (1-(r\Omega/c)^2)^{-1}$, where $\Omega$ - angular velocity of the pulsar rotation. The magneto centrifugal mechanism provides acceleration of the electrons to the energy which is sufficient to explain the observed VHE pulsed $\gamma$-rays from Crab pulsar.