HIGH-PRECISION TIMING OF PSR J1713+0747 - SHAPIRO DELAY

We present results based on timing of the binary millisecond pulsar J1713+0747 for 22 months through 1994 February. We have measured its annual parallax, pi = (0.9 +/- 0.3) mas, as well as its proper motion, mu = (6.4 +/- 1.0) milliarcsec (mas) yr(-1). We detect a signature in the timing residuals that is most naturally interpreted as the general relativisitic ''Shapiro delay at the 2 sigma confidence level, we find the companion mass, m(2) > 0.27 M(.), while the pulsar mass, m(1) > 1.2 M.. Upper limits on both masses can only be obtained by imposing additional constraints on the system, such as requiring that general relativity be valid in the strong-field limit. With a post-fit weighted root mean square timing residual of approximately 0.4 mu s, and a characteristic age of roughly 9 x 10(9) yr, this pulsar is potentially the most stable celestial clock among all known pulsars.