Gravitational-radiation losses from the pulsar white-dwarf binary PSR J1141 6545

Pulsars in close binary systems with white dwarfs or other neutron stars make ideal laboratories for testing the predictions of gravitational radiation and self-gravitational effects. We report new timing measurements of the pulsar white-dwarf binary PSR J1141 6545. The orbit is found to be decaying at a rate of 1.04±0.06 times the general relativistic prediction and the Shapiro delay is consistent with the orbital inclination angle derived from scintillation measurements. The system provides a unique testbed for tensor-scalar theories of gravity. Our measurements place stringent constraints in the theory space, with a limit of α₀²<2.1×10^-5 for weakly nonlinear coupling and an asymptotic limit of α₀²<3.4×10^-6 for strongly nonlinear coupling (where α₀ is the linear coupling strength of matter to an underlying scalar field), which is nearly 3 times smaller than the Cassini bound (α₀²≈10^-5).