JPL pulsar timing observations. I. The VELA pulsar.

It is found through an analysis of 12 years of arrival time data for PSR 0833-45, by fitting a model of the pulse period to the data in a least-squares sense, that there exist regions of exceptionally stable behavior in which rms residuals are typically about 40 microsec. In addition, each residual exhibits a significant period parameter second derivative which is found to change little within a given interjump era. Parameter changes in the period P, and the derivatives introduced by each of the four large observed jumps in period, are recomputed to demonstrate that the post-jump decay is nearly exponential in form. It is found that random fluctuations in P are an order of magnitude less than the systematic variations caused by the second derivative period parameter, whose component associated with the general slowdown of the pulsar can be reliably measured when the observations span 55 years or more.