Force-Free Approximation — The Magnetosphere of Radio Pulsars

Abstract

The general view of the radio pulsar activity seems to have been established over many years. On the other hand, some fundamental problems are still to be solved. It is, first of all, the problem of the physical nature of the coherent radio emission of pulsars. In particular, as in the 1970 s, there is no common view of the problem of the coherent radio emission mechanism of a maser or an antenna type.Moreover, there is no common view of the pulsar magnetosphere structure. The point is that the initial hypothesis for the magnetodipole energy loss mechanism is, undoubtedly, unrealistic. Therefore, the problem of the slowing-down mechanism can be solved only if the magnetosphere structure of neutron stars is established. However, a consistent theory of radio pulsar magnetospheres has not yet been developed. Thus, the structure of longitudinal currents circulating in the magnetosphere has not been specified and, hence, the problems of neutron star braking, particle acceleration, and energy transport beyond the light cylinder have not been solvedeither. The theory of the inner structure of neutron stars is also far from completion. Naturally, it is impossible to dwell on all these problems here and, therefore, we discuss in detail only the problems directly associated with themain theme of this book, viz., the theory of radio pulsar magnetospheres. The first two sections consider the basic physical processes in neutron star magnetospheres and the secondary plasma generation mechanism. Then we formulate a pulsar equation, i.e., the force-free Grad–Shafranov equation in flat space providing the correct determination of the energy losses of radio pulsars. Further, the exact analytical solutions obtained for radio pulsar magnetospheres are also discussed in detail. It is demonstrated that, within the force-free approximation, a self-consistent theory cannot be formulated. Finally, the current pulsar magnetosphere models are analyzed.