Magnetic fields and the $\dot P - P$ diagram for radio pulsars

Abstract

Various mechanisms for the loss of angular momentum of neutron stars are analyzed. Theoretical predictions about the evolution of the period are compared with the observed distribution of pulsars on the log$\dot P$log(P) diagram. Pulsars with short periods (P≤0.1 s) cannot be fit well by any of the models considered. Their braking index is n=−1, which requires the development of a new braking mechanism. The evolution of pulsars with P>1.25 s is described by the law $\dot P \propto P^2$, probably due to processes internal to the neutron stars. The observational data for pulsars with 0.1<P≤1.25 s can be fit with a hybrid model incorporating internal processes and magnetic-dipole losses. The magnetic fields in pulsar catalogs should be recomputed in accordance with the results obtained. For example, the magnetic fields obtained for two magnetars with P=5.16 s and P=7.47 s are B _s =1.7×10¹³ and 2.9×10¹³ G, which are lower than the critical field B _cr=4.4×10¹³ G. For a substantial fraction of pulsars, their characteristic ages $\tau = P/2\dot P$ cannot serve as measures of their real ages.