Long-Term Phase-coherent X-Ray Timing of PSR-B0540-69

We present a new phase-coherent timing analysis for the young, energetic pulsar PSR-B0540-69 using 7.6 yr of data from the Rossi X-Ray Timing Explorer. We measure the braking index, n = 2.140 +- 0.009, and discuss our measurement in the context of other discordant values reported in the literature. We present an improved source position from the phase-coherent timing of the pulsar, to our knowledge, the first of its kind from X-ray pulsar timing. In addition, we detect evidence for a glitch that had been previously reported but later disputed. The glitch occurred at MJD 51,335 +12 with (delta)(nu)/(nu) = (1.4 +- 0.2) * 10^-9 and (delta).../... = (1.33 +- 0.02) * 10^-4. We calculate that the glitch activity parameter for PSR-B0540-69 is 2 orders of magnitude smaller than that of the Crab pulsar, which otherwise has very similar properties. This suggests that neutron stars of similar apparent ages, rotation properties, and inferred dipolar B fields can have significantly different internal properties.