Abstract:
We investigate the statistical effects of non-discrete timing irregularities on observed radio pulsar braking indices using correlations between the measured anomalous frequency second derivatives (¨ obs) and some parameters that have been widely used to quantify pulsar timing fluctuations [the timing activity parameter (A), the amount of timing fluctuations absorbed by the cubic term ( R23) and a measure of pulsar rotational
stability ( z)] in a large sample of 366 Jodrell Bank Observatory (JBO) radio pulsars. The result demonstrates that anomalous braking indices are largely artefacts produced by aggregations of fluctuations that occur within or outside the pulsar system. For a subsample of 223 normal radio pulsars whose observed timing activity over timescales of ∼ 10−40 years appeared consistent with instabilities in rotation of the underlying neutron stars (or timing noise), |¨ obs| strongly correlates (with correlation coefficient |r| ∼ 0.80 − 0.90) with the pulsar timing activity parameters (TAPs) and spin-down properties. On the other hand, no meaningful correlations (r < 0.3) were found between ¨ obs and the timing activity diagnostics and spin-down parameters in the remaining 143 objects, whose timing activity appears significantly dominated by white noise fluctuations. Current result can be bettter understood if timing noise activity in isolated pulsars originates from intrinsic spin-down processes of the underlying neutron stars, while white noise fluctuations arise largely from processes external to the pulsar system.
