* Astronomy

Blobrana · L

RE: PSR J1738+0333

Blobrana · L

Title: PSR J1738+0333: The First Millisecond Pulsar + Pulsating White Dwarf Binary
Author: Mukremin Kilic, J. J. Hermes, A. Gianninas, Warren R. Brown

We report the discovery of the first millisecond pulsar with a pulsating white dwarf companion. Following the recent discoveries of pulsations in extremely low-mass (ELM, <0.3 Msol) white dwarfs (WDs), we targeted ELM WD companions to two millisecond pulsars with high-speed Gemini photometry. We find significant optical variability in PSR J1738+0333 with periods between roughly 1790-3060 s, consistent in timescale with theoretical and empirical observations of pulsations in 0.17 Msol He-core ELM WDs. We additionally put stringent limits on a lack of variability in PSR J1909-3744, showing this ELM WD is not variable to <0.1 per cent amplitude. Thanks to the accurate distance and radius estimates from radio timing measurements, PSR J1738+0333 becomes a benchmark for low-mass, pulsating WDs. Future, more extensive time-series photometry of this system offers an unprecedented opportunity to constrain the physical parameters (including the cooling age) and interior structure of this ELM WD, and in turn, the mass and spin-down age of its pulsar companion.

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Blobrana · L

Title: The relativistic pulsar-white dwarf binary PSR J1738+0333 II. The most stringent test of scalar-tensor gravity
Authors: Paulo C. C. Freire, Norbert Wex, Gilles Esposito-Farèse, Joris P. W. Verbiest, Matthew Bailes, Bryan A. Jacoby, Michael Kramer, Ingrid H. Stairs, John Antoniadis, Gemma H. Janssen

We report the results of a 10-year timing campaign on PSR J1738+0333, a 5.85-ms pulsar in a low-eccentricity 8.5-hour orbit with a low-mass white dwarf companion (...) The measurements of proper motion and parallax allow for a precise subtraction of the kinematic contribution to the observed orbital decay; this results in a significant measurement of the intrinsic orbital decay: (-25.9 ±3.2) x 10^{-15} s/s. This is consistent with the orbital decay from the emission of gravitational waves predicted by general relativity, (-27.7 +1.5/-1.9) x 10^{-15} s/s (...). This agreement introduces a tight upper limit on dipolar gravitational wave emission, a prediction of most alternative theories of gravity for asymmetric binary systems such as this. We use this limit to derive the most stringent constraints ever on a wide class of gravity theories, where gravity involves a scalar field contribution. When considering general scalar-tensor theories of gravity, our new bounds are more stringent than the best current solar-system limits over most of the parameter space, and constrain the matter-scalar coupling constant {\alpha}_0^2 to be below the 10^{-5} level. For the special case of the Jordan-Fierz-Brans-Dicke, we obtain the one-sigma bound {\alpha}_0^2 < 2 x 10^{-5}, which is within a factor two of the Cassini limit. We also use our limit on dipolar gravitational wave emission to constrain a wide class of theories of gravity which are based on a generalisation of Bekenstein's Tensor-Vector-Scalar gravity (TeVeS), a relativistic formulation of Modified Newtonian Dynamics (MOND).

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