Timing Observations of the X-Ray Pulsar SMC X-1

The EXOSAT observatory was pointed at the X-ray pulsar SMC X-1 on five occasions late in 1984. These were at intervals of approximately 3.892 days, the orbital period. The source was in a bright state for all five observations, thus permitting precise determination of the pulsation wave form and its variability, the pulse period and its derivative, and the binary epoch. Results are presented and discussed in the context of the historical record. Interpretation will consider the possibility of an anomalous change in the pulsar spin rate or in the orbital evolution.