A second measurement of a pulsar breaking index

The braking index, n, of a pulsar is a fundamental parameter of pulsar electrodynamics. Simple theoretical arguments predict n=3, whereas the only previously measured value (for the Crab pulsar) is 2.515+-0.005. Here the authors present radio timing observations of the X-ray and radio pulsar, PSR1509-58, made over an approximately 2-year interval, which yield a second significant measurement of n=2.83+-0.03, more than that for the Crab pulsar, but less than the canonical value of 3. Despite the large period first derivative of PSR1509-58, there is no evidence for glitches or random irregularities in the period. (author)