Spin-down of pulsars

The theories on the spin-down of pulsars are roughly grouped into two: those involving stellar wind and those which do not. In both groups, the spin-down rate is predominantly governed by the properties of the stars, while surrounding nebula or interstellar material plays no significant role. If it is assumed that neutron stars are created by supernova explosion, it may be expected that the supernova remnant will disperse after a long time, and interstellar material will have some effect on the spin-down rate of pulsars. Such effect may play an important role in the spin-down of magnetic non-degenerate stars, and the similar effect may become important in the long term spin-down of pulsars. In order to determine this problem, the oblique rotator model for pulsars and the magnetic frictional braking model for non-degenerate stars were compared. At present, the self-consistent theory on the evolution of the magnetosphere of pulsars or the spin-down of magnetic stars in general does not exist. According to the estimation, the period of the same order as the longest period of known pulsars was obtained, but it is not clear whether magnetic frictional braking is responsible for the turn-off mechanism of pulsars. Perhaps there is more than one cause for the turning-off of pulsars, and stars slow down and rest within a finite time, whereas in usual pulsar theories, it is infinite. It is reasonable to assume that pulsars are surrounded by interstellar medium. (Kako, I.)