Effects of Spin Properties on Braking Indices of 208 Glitching Pulsars

Abstract

Pulsars are stars that emit electromagnetic radiation in a definite time interval. Detailed study of the long-term timing observations of pulsars indicate that the predictable smooth spin- down of pulsars is predisposed to discrete fluctuations known as glitch. The rotation frequency of pulsars decays with time as quantified by the braking index (<i>n</i>). The braking indices have been known to have no consequence on the quantities like obliquity angle evolution or complex high-order multipole structure but on the spin properties of the pulsars. In the canonical model of the theory of braking indices, <i>n</i> = 3 for all pulsars, but observational information has shown that <i>n</i> ≠ 3, indicating that the canonical model requires reconsideration. Using the Australian Telescope National Facility (ATNF) pulsar catalogue, we selected 208 pulsars with 670 glitches and used the distributions of the spin properties to statistically investigate their effects on the braking indices. We computed the braking indices of these pulsars using the theoretical method and observed that the braking index is much smaller for very young pulsars (10⁴-10⁷) which have been observed to show more glitch activity than their old, stable counterparts. A simple regression analysis of our data show that spin properties of pulsar are more than 65% correlated with the magnitude of pulsar braking index. The implications of the spin properties on braking indices on long timescales are discussed.