Formation of filament-like structures in the pulsar magnetosphere and the short-term variability of pulsar emission

摘要

Context. Magnetohydrodynamic (MHD) instabilities can play an important role in the dynamics of the pulsar magnetosphere and can be responsible for the formation of various structures. Aims. We consider the instability caused by a gradient of the magnetic pressure, which can occur in a non-neutral magnetospheric plasma of the pulsars. Methods. Stability is discussed by means of a linear analysis of the force-free MHD equations. Results. We argue that the pulsar magnetospheres are always unstable. The unstable disturbances have a form of filaments directed along the magnetic field lines with plasma motions being almost parallel (or anti-parallel) to the magnetic field. The growth rate of instability is high and can reach a fraction of ck, where k is the wavevector of unstable disturbances. The instability can be responsible for fluctuations of plasma and the short-term variability of pulsar emission.