2002ApJ...567.1067G

We report on long-term monitoring of three anomalous X-ray pulsars (AXPs) using the Rossi X-Ray Timing Explorer (RXTE). We present a phase-coherent timing ephemeris for 4U 0142+61 and show that it has rotated with high stability over 4.4 yr, with rms phase deviations of 7% of the pulse period from a simple fit including only ν and ν{dot}. We report on the continued timing stability of 1E 2259.1+586, for which phase coherence has now been maintained over 4.5 yr, as well as on the detection of a significant ν{ddot} in 1.4 yr of monitoring of 1RXS J170849.0-400910, consistent with recovery following a glitch. We note a correlation in which timing stability in AXPs decreases with increasing ν{dot}. The timing stability of soft gamma repeaters in quiescence is consistent with this trend, given their large spin-down rates. This trend is similar to one seen in radio pulsars, suggesting a connection between the three populations. We find no large variability in pulse morphology as a function of time. We present high signal-to-noise ratio average pulse profiles for each AXP and consider them as a function of energy. We find a variety of different behaviors and consider possible trends in the data. We also find no large variations in pulsed flux and set 1 σ upper limits of ∼20%-30% of the mean.