Title: PSR J1141-6545: a powerful laboratory of GR and tensor-scalar theories of gravity Authors: J. P. W. Verbiest, N. D. R. Bhat, M. Bailes

Pulsars in close binary systems have provided some of the most stringent tests of strong-field gravity to date. The pulsar--white-dwarf binary system J1141-6545 is specifically interesting due to its gravitational asymmetry which makes it one of the most powerful probes of tensor-scalar theories of gravity. We give an overview of current gravitational tests provided by the J1141-6545 binary system and comment on how anomalous accelerations, geodetic precession and timing instabilities may be prevented from limiting future tests of gravity to come from this system.

Title: Gravitational-radiation losses from the pulsar-white-dwarf binary PSR J1141-6545 Authors: N. D. Ramesh Bhat, Matthew Bailes, Joris P. W. Verbiest

Pulsars in close binary orbit around another neutron star or a massive white dwarf 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, providing strong evidence that such asymmetric systems have gravitational wave losses that are consistent with general relativity. 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 test-bed for tensor-scalar theories of gravity; our current measurements place stringent constraints in the theory space, with a limit of \alpha_0² < 2.1 \times 10^{-5} for weakly non-linear coupling and an asymptotic limit of \alpha_0² < 3.4 \times 10^{-6} for strongly non-linear coupling, where \alpha_0 is the linear coupling strength of matter to an underlying scalar field. This asymptotic limit is nearly three times smaller than the Cassini bound (\alpha_0² ~ 10^{-5}).