Understanding the residual patterns of timing solutions of radio pulsars with a model of magnetic field oscillation

TL;DR

This paper models pulsar timing residuals using magnetic field oscillations, successfully fitting observed patterns and suggesting a common oscillation mode in pulsars' magnetic fields throughout their lifetimes.

Contribution

It introduces a magnetic field oscillation model that explains and reproduces various timing residual patterns with few parameters, supported by simulations.

Findings

Most residual patterns can be reproduced by the model.

A single magnetic field oscillation mode is common in pulsars.

Multiple modes may exist during pulsars' evolution.

Abstract

We explain some phenomena existing generally in the timing residuals: amplitude and sign of the second derivative of a pulsar's spin-frequency ($\ddot\nu$), some sophisticated residual patterns, which also change with the time span of data segments. The sample is taken from Hobbs et al.\,(2010), in which the pulsar's spin-frequency and its first derivative have been subtracted from the timing solution fitting. We first classify the timing residual patterns into different types based on the sign of $\ddot\nu$. Then we use the magnetic field oscillation model developed in our group \citep{zhang12a} to fit successfully the different kinds of timing residuals with the Markov Chain Monte Carlo method. Finally, we simulate the spin evolution over 20 years for a pulsar with typical parameters and analyze the data with the conventional timing solution fitting. By choosing different segments of the simulated data, we find that most of the observed residual patterns can be reproduced successfully. This is the first time that the observed residual patterns are fitted by a model and reproduced by simulations with very few parameters. From the distribution of the different residual patterns in the $P-\dot P$ diagram, we argue that (1) a single magnetic field oscillation mode exists commonly in all pulsars throughout their lifetimes; (2) there may be a transition period over the lifetimes of pulsars, in which multiple magnetic field oscillation modes exist.