* Astronomy

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}).

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