An improved test of the strong equivalence principle with the pulsar in a triple star system

Abstract

Context. The gravitational strong equivalence principle (SEP) is a cornerstone of the general theory of relativity (GR). Hence, testing the validity of SEP is of great importance when confronting GR, or its alternatives, with experimental data. Pulsars that are orbited by white dwarf companions provide an excellent laboratory, where the extreme difference in binding energy between neutron stars and white dwarfs allows for precision tests of the SEP via the technique of radio pulsar timing. Aims. To date, the best limit on the validity of SEP under strong-field conditions was obtained with a unique pulsar in a triple stellar system, PSR J0337+1715. We report here on an improvement of this test using an independent data set acquired over a period of 6 years with the Nançay radio telescope. The improvements arise from a uniformly sampled data set, a theoretical analysis, and a treatment that fixes some short-comings in the previously published results, leading to better precision and reliability of the test. Methods. In contrast to the previously published test, we use a different long-term timing data set, developed a new timing model and an independent numerical integration of the motion of the system, and determined the masses and orbital parameters with a different methodology that treats the parameter Δ, describing a possible strong-field SEP violation, identically to all other parameters. Results. We obtain a violation parameter Δ = ( + 0.5 ± 1.8) × 10−6 at 95% confidence level, which is compatible with and improves upon the previous study by 30%. This result is statistics-limited and avoids limitation by systematics as previously encountered. We find evidence for red noise in the pulsar spin frequency, which is responsible for up to 10% of the reported uncertainty. We use the improved limit on SEP violation to place constraints on a class of well-studied scalar-tensor theories, in particular we find ωBD > 140 000 for the Brans-Dicke parameter. The conservative limits presented here fully take into account current uncertainties in the equation for state of neutron-star matter.

Gravity, Geodesy and Fundamental Physics with BepiColombo’s MORE Investigation

“…BepiColombo will be able to test the strong equivalence principle in the weak field regime. A comparison with the recent test carried out in a different regime with the data analysis of the triple pulsar system (Archibald et al 2018;Voisin et al 2020) provides an upper bound on η at the level of 10 −6 .…”

Gravity Tests with Radio Pulsars

“…Already a few years after its discovery, a tight limit of order few times 10 −6 on a violation of GWEP has been obtained from PSR J0337+1715 [115]. The so far best limit comes from regular timing observations with the Nançay radio telescope [116]:…”

“…An alternative approach to compare pulsar experiments with tests in other regimes, like the Solar System or LIGO/Virgo observations, is the use of a theory-dependent framework [34]. For the triple-system test, such a comparison has been done on the basis of DEF gravity [115,116]. In DEF gravity (cf.…”

“…The region above a curve is excluded by the corresponding experiment. Pulsar constraints are based on the rather stiff EOS BSk22 [99], which generally gives conservative limits (see [116] for a discussion, and a more EOS-agnostic approach). The β 0 = 0 line corresponds to Jordan-Fierz-Brans-Dicke gravity.…”

A comparative analysis of pulse time-of-arrival creation methods

“…Their extremely stable rotation periods make MSPs ideal laboratories for testing a diversity of extreme astrophysical phenomena that cannot be accessed on Earth. Their applications include investigating turbulence and structures of the interstellar medium (Keith et al 2013;Lam et al 2018;Donner et al 2019), testing relativistic gravity (Taylor & Weisberg 1982;Archibald et al 2018;Voisin et al 2020), building a pulsar-based time standard (Hobbs et al 2012(Hobbs et al , 2020, constraining masses in the Solar System (Champion et al 2010;Caballero et al 2018), measuring the magnetic field structure in the Galaxy (Han et al 2018;Gentile et al 2018), and detecting gravitational jun.wang.ucas@gmail.com radiation (e.g. Shannon et al 2015;Lentati et al 2016;Arzoumanian et al 2020).…”