On the peculiarities in the rotational frequency evolution of isolated neutron stars

Abstract

The measurements of pulsar frequency second derivatives have shown that they are 10 2 −10 6 times larger than expected for standard pulsar spin-down law, and are even negative for about half of pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters ν,ν andν of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation betweenν andν for bothν > 0 andν < 0, as well as between ν andν. We interpret these dependencies as evolutionary ones due toν being nearly proportional to the pulsars' age. The derived statistical relations as well as "anomalous" values ofν are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore, consists of secular change of ν ev (t),ν ev (t) andν ev (t) according to the power law with n ≈ 5, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that-several decades.