High-precision timing of PSR J1713+0747: Shapiro delay

We present results based on timing of the binary millisecond pulsar (MSP) 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. We detect a signature in the timing residuals that is most naturally interpreted as the general relativistic 'Shapiro delay;' at the 2 sigma confidence level, we find the companion mass, m₂ is greater than 0.27 solar mass, while the pulsar mass, m₁ is greater than 1.2 solar mass. 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 (rms) timing residual of approximately 0.4 microsec, and a characteristic age of roughly 9 x 10⁹ yr, this pulsar is potentially the most stable celestial clock among all known pulsars.