A simple analysis of period noise in binary X-ray pulsars

Abstract

A simple method is presented for determining whether the noise in the pulse period history of X-ray pulsars can be described by a random walk process. This is accomplished by calculating the mean difference in angular velocity between different observations as a function of the time interval between these observations. The method is applied to 10 X-ray pulsars for which more than 10 period determinations are available. For Vela X-1, earlier results that the pulse period behavior is very well fitted by a random walk in period is confirmed. In GX 301-2 the pulse period behavior is also consistent with a random walk. Analysis of the pulse period history of three X-ray pulsars with a Be companion shows that a random walk is not consistent with the data.