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F.E. Marshall, W. Zhang (NASA/GSFC), E.V. Gotthelf (Columbia U.), J. Middleditch (LANL), Q.D. Wang (U. Mass.)
We report the results of an extensive timing monitoring campaign of PSR J0537-6910, the 16-ms pulsar in the Large Magellanic Cloud, using data acquired with the Rossi X-ray Timing Explorer. A set of 130 pointed X-ray observations during the 2.6 year campaign reveals a steady spin-down interrupted by 6 glitch events. This glitch rate is comparable to the highest seen for any pulsar. We have performed pulse timing analysis which successfully maintains phase between observations, after allowing for the observed glitches. The mean glitch amplitude was a change in frequency of \Delta\nu/\nu = 0.36\times 10-6 or a glitch activity parameter Ag of 0.83/yr. Two types of transient behavior are frequently seen near the glitches. First, phases measured during observations for several weeks after a glitch are often slightly below the extrapolation of best-fit model for the subsequent post-glitch data. It appears that a small fraction of the sudden increase in frequency decays with an e-folding time scale of about a week. Second, the initial indication of a glitch is often the detection of a large phase error with no measurable change in pulsar frequency. This precursor typically precedes by many days the large change in frequency associated with the glitch. Despite this extreme timing activity, the spin-down of the pulsar continues to average -1.9743\times 10-10 Hz/s. The evolution of the rotation rate during the longest glitch-free interval of 266 days indicates a braking index significantly higher than the value for pure magnetic dipole braking in a vacuum. The exact value of the braking index requires an accurate position for the pulsar.