W. Zhang et al., A phase-connected braking index measurement for the Large Magellanic Cloudpulsar PSR B0540-69, ASTROPHYS J, 554(2), 2001, pp. L177-L180
We report the results of an extensive monitoring campaign of PSR B0540-69,
the 50 ms pulsar in the Large Magellanic Cloud, using data acquired with th
e Rossi X-Ray Timing Explorer. A set of 45 pointed X-ray observations spann
ing 1.2 yr reveals a steady spin-down interrupted by a single glitch event,
the first recorded for this young, rotation-powered pulsar. The quality of
the data allowed us to perform a pulse-timing analysis that successfully m
aintains cycle count between observations, after allowing for the observed
glitch. The glitch event occurred on MJD 51,325 +/- 45 (90% CL error) and i
s characterized by a change in frequency of Delta nu/nu = 1.90 +/- 0.04 x 1
0(-9) and in frequency derivative of. By phase-linking the data set we prov
ide a definitive measurement of the spin frequency of the pulsar and its fi
rst and second derivatives. These translate into a braking index of n = 1.8
1 +/- 0.07, significantly lower than reported previously for this source us
ing measurements that could not be phase-linked unambiguously.