Profile-shape stability and phase-jitter analyses of millisecond pulsars

Millisecond pulsars (MSPs) have been studied in detail since their discovery in 1982. The integrated pulse profiles of MSPs appear to be stable, which enables precision monitoring of the pulse times of arrival (TOAs). However, for individual pulses the shape and arrival phase can vary dramatically; this is known as pulse jitter. In this paper, we investigate the stability of integrated pulse profiles for five MSPs and estimate the amount of jitter for PSR J0437-4715. We do not detect intrinsic profile-shape variation based on integration times from similar to 10-100s with the provided instrumental sensitivity. For PSR J0437-4715, we calculate the jitter parameter to be f(J) = 0.067 +/- 0.002 and demonstrate that the result is not significantly affected by instrumental TOA uncertainties. Jitter noise is also found to be independent of observing frequency and bandwidth around 1.4 GHz on frequency scales of <100 MHz, which supports the idea that pulses within a narrow frequency scale are equally jittered. In addition, we point out that pulse jitter would limit TOA calculation for timing observations with future telescopes like the Square Kilometre Array and the Five hundred metre Aperture Spherical Telescope. A quantitative understanding of pulse-profile stability and the contribution of jitter would enable improved TOA calculations, which are essential for ongoing endeavours in pulsar timing such as detection of the stochastic gravitational wave background.