Measurement of relativistic orbital decay in the PSR B1534+12 binary system

We have made timing observations of binary pulsar PSR B1534+12 with radio t elescopes at Arecibo, Green Bank, and Jodrell Bank. By combining our new ob servations with data collected up to seven years earlier, we obtain a signi ficantly improved solution for the astrometric, spin, and orbital parameter s of the system. For the first time in any binary pulsar system, no fewer t han five relativistic or "post-Keplerian" orbital parameters are measurable with useful accuracies in a theory-independent way. We find the orbital pe riod of the system to be decreasing at a rate close to that expected from g ravitational radiation damping according to general relativity, although th e precision of this test is limited to about 15% by the otherwise poorly kn own distance to the pulsar. The remaining post-Keplerian parameters are all consistent with one another and all but one of them have fractional accura cies better than 1%. By assuming that general relativity is the correct the ory of gravity, at least to the accuracy demanded by this experiment, we fi nd the masses of the pulsar and companion star each to be 1.339 +/- 0.003 M . and the system's distance to be d = 1.1 +/- 0.2 kpc, marginally larger th an the d approximate to 0.7 kpc estimated from the dispersion measure. The increased distance reduces estimates of the projected rate of coalescence o f double neutron star systems in the universe, a quantity of considerable i nterest for experiments with terrestrial gravitational wave detectors such as the Laser Interferometer Gravitational-Wave Observatory.