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

Biryukov, A.; Beskin, G.; Karpov, S.

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

Authors

Biryukov, A.

Beskin, G.

Karpov, S.

Description

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 $ν$, $\dot ν$ and $\ddot ν$ of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between $\ddot ν$ and $\dot ν$ for both $\ddotν> 0$ and $\ddotν< 0$, as well as between $ν$ and $\dotν$. We interpret these dependencies as evolutionary ones due to $\dotν$ being nearly proportional to the pulsars' age. The derived statistical relations as well as "anomalous" values of $\ddotν$ are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore, consists of secular change of $ν_{ev}(t)$, $\dotν_{ev}(t)$ and $\ddotν_{ev}(t)$ according to the power law with $n \approx 5$, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that timespan -- several tens of years.
4 pages, 3 figures. Accepted for publication in ApSS, in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 2006; eds. S. Zane, R. Turolla and D. Page