Measurement of Relativistic Orbital Decay in thePSR B 1534 + 12 Binary SystemI

We have made timing observations of binary pulsar PSR B1534+12 with radio telescopes at Arecibo, Green Bank, and Jodrell Bank. By combining our new observations with data collected up to seven years earlier, we obtain a signiicantly improved solution for the astrometric, spin, and orbital parameters of the system. For the rst time in any binary pulsar system, no fewer than ve relativistic or \post-Keplerian" orbital parameters are measurable with useful accuracies in a theory-independent way. We nd the orbital period of the system to be decreasing at a rate close to that expected from gravitational radiation damping, according to general relativity, although the precision of this test is limited to about 15% by the otherwise poorly known distance to the pulsar. The remaining post-Keplerian parameters are all consistent with one another and all but one of them have fractional accuracies better than 1%. By assuming that general relativity is the correct theory of gravity, at least to the accuracy demanded by this experiment, we nd the masses of the pulsar and companion star each to be 1:339 0:003M and the system's distance to be d = 1:1 0:2 kpc, marginally larger than the d 0:7 kpc estimated from the dispersion measure. The increased distance reduces estimates of the projected rate of coalescence of double neutron-star systems in the universe, a quantity of considerable interest for experiments with terrestrial gravitational wave detectors such as LIGO.