Seventeenth Marcel Grossmann Meeting

Stochastic and secular anomalies in measurements of pulsar braking indices

Not scheduled

20m

Aurum, the ‘Gabriele d’Annunzio’ University and ICRANet

Talk in a parallel session High energy astrophysics High energy astrophysics

Speaker

Dr Andrés Vargas (Research Fellow, The University of Melbourne)

Description

Stochastic (i.e. the achromatic component of timing noise unrelated to interstellar propagation) and secular variations in the spin frequency $\nu$ of a rotation-powered pulsar complicate the interpretation of the measured second derivative of the spin frequency $\ddot{\nu }$, and hence the braking index, $n$, in terms of a power-law spin-down torque $\propto {\nu }^{n_{\mathrm{p}\mathrm{l}}}$. Both categories of variation can lead to measurements of $\ddot{\nu }$ which yield anomalous braking indices, i.e. $|n|=|\nu \ddot{\nu }/{\dot{\nu }}^2|\gg 1$, where the overdot symbolizes a derivative with respect to time. In this talk, I will discuss the following three key results. First, the combined effect of stochastic and secular deviations from pure power-law spin down on measurements of $\ddot{\nu }$ and its implications in observationally constraining $n$. Second, how the variance of $\ddot{\nu }$ (or equivalently $n$) satisfies a falsifiable, analytical result derived from first principles. We quantify said variance through analytic calculations, Monte Carlo simulations involving synthetic data from a phenomenological model, and modern Bayesian techniques. Third, how the variance of $\ddot{\nu }$ may be applied to real astronomical situations to predict or interpret the measured braking index $n$.