2022A&A...668A.187G

We report the results of timing observations of PSR J1952+2630, a 20.7 ms pulsar in orbit with a massive white dwarf companion. We performed six months of timing observations with the Arecibo radio telescope in 2020 and used data from FAST from 2021. Together with previously published data, this represents a total timing baseline of 11 yr since the discovery of the pulsar in 2010. For the first time, we present a polarimetric profile of the pulsar and determine its rotation measure (RM), - 145.79 ± 0.15 rad m^–2. With the increased timing baseline, we obtain improved estimates for astrometric, spin, and binary parameters for this system. In particular, we obtain an imporvement of an order of magnitude on the proper motion, and, for the first time, we detect three post-Keplerian parameters in this system: the advance of periastron $ \dot{\omega} $, the orbital decay Ṗ_b, and the Shapiro delay (measured in the form of the h₃ parameter). With the detection of these relativistic effects, we constrain the pulsar mass to 1.20$ ^{+0.28}_{-0.29} $M_⊙ and the mass of its companion to 0.97$ ^{+0.16}_{-0.13} $M_⊙. The current value of Ṗ_b is consistent with the General Relativity expectation for the masses obtained using $ \dot{\omega} $ and h₃. The excess ($ 4.2 ^{+70.2}_{-73.1} \,\rm fs \, s^{-1} $) represents a limit on the emission of dipolar gravitational waves (GWs) from this system. This results in a limit on the difference in effective scalar couplings for the pulsar and companion (predicted by scalar-tensor theories of gravity; STTs) of |α_p - α_c|< 4.8 × 10^–3 (68% C.L.), which does not yield a competitive test for STTs. However, our simulations of future timing campaigns of this system, based on the timing precision we have achieved with FAST, show that by 2032, the precision of Ṗ_b and $ \dot{\omega} $ will allow for much more precise masses and much tighter constraints on the orbital decay contribution from dipolar GWs, resulting in |α_p - α_c|< 1.3 × 10^–3 (68% C.L.). For comparison, we obtain |α_p - α_c|< 1.9 × 10^–3 and < 3.3 × 10^–3 from PSR J1738+0333 and PSR J2222-0137, respectively. We also present the constraints this system will place on the {α₀, β₀} parameters of Damour-Esposito-Farèse (DEF) gravity by 2032. They are comparable to those of PSR J1738+0333. Unlike PSR J1738+0333, PSR J1952+2630 will not be limited in its mass measurement and has the potential to place even more restrictive limits on DEF gravity in the future. Further improvements to this test will likely be limited by uncertainties in the kinematic contributions to Ṗ_b because of the lack of precise distance measurements.