Generic tests of the existence of the gravitational dipole radiation and the variation of the gravitational constant

Abstract

We present results from the high-precision timing analysis of the pulsar-white dwarf (WD) binary PSR J1012+5307 using 15 years of multitelescope data. Observations were performed regularly by the European Pulsar Timing Array (EPTA) network, consisting of Effelsberg, Jodrell Bank, Westerbork and Nançay. All the timing parameters have been improved from the previously published values, most by an order of magnitude. In addition, a parallax measurement of π = 1.2(3) mas is obtained for the first time for PSR J1012+5307, being consistent with the optical estimation from the WD companion. Combining improved 3D velocity information and models for the Galactic potential, the complete evolutionary Galactic path of the system is obtained. A new intrinsic eccentricity upper limit of e < 8.4 × 10 −7 is acquired, one of the smallest calculated for a binary system and a measurement of the variation of the projected semimajor axis also constrains the system's orbital orientation for the first time. It is shown that PSR J1012+5307 is an ideal laboratory for testing alternative theories of gravity. The measurement of the change of the orbital period of the system oḟ P b = 5(1) × 10 −14 is used to set an upper limit on the dipole gravitational wave emission that is valid for a wide class of alternative theories of gravity. Moreover, it is shown that in combination with other binary pulsars PSR J1012+5307 is an ideal system to provide selfconsistent, generic limits, based only on millisecond pulsar data, for the dipole radiation and the variation of the gravitational constantĠ.

New pulsar limit on local Lorentz invariance violation of gravity in the standard-model extension

“…Interestingly, such mass measurements were already obtained, thanks to the optical observations of the WD companions, with the three small-eccentricity binary pulsars we are to use [46,[48][49][50]. From optical observations, the mass of the WD can be inferred based on the WD atmosphere models and, from the ratio of the (projected) orbital velocities of the WD (from optical spectroscopy) and the pulsar (from radio timing), the mass ratio of two components can be derived.…”

“…(11-13)). Relevant parameters for the test of these systems, from radio timing and optical spectroscopy, are tabulated in Table I (see the original publications [46][47][48] for details).…”

“…Fortunately, for some NS-WD systems, we can use the orbitally phase-resolved optical spectroscopy of the white dwarf to separate its sinusoidally varying (projected) orbital velocity and its nearly constant systematic radial velocity [48][49][50]. We will make use of three small-eccentricity NS-WD binaries with radial velocity measurements, namely PSRs J1012+5307 [46], J1738+0333 [47] and J0348+0432 [48].…”

“…(12-13) instead ofė andω. Because for some pulsars, x,η, andκ were not reported along with other timing parameters in their timing solutions pub- [46], J1738+0333 [47], and J0348+0432 [48] for the test, from radio timing and optical spectroscopy observations. Parenthesized numbers represent the 1-σ uncertainty in the last digits quoted.…”

“…As mentioned, to meet the requirements listed above, we choose PSRs J1012+5307 [46], J1738+0333 [47], and J0348+0432 [48] to perform the test ofs TT . They are all well-timed small-eccentricity NS-WD binaries with both radio and optical observations.…”