Classical and general relativistic post-Keplerian effects in binary pulsars hosting fast rotating main sequence stars
Abstract
We consider a binary system composed of a pulsar and a massive, fast rotating, highly distorted main sequence star of mass M, spin angular momentum S , dimensionless mass quadrupole moment J_2, equatorial and polar radii R_ {e}, R_ {p}, flattening ν \doteq (R_ {e}-R_ {p})/R_ {e}, and ellipticity ɛ \doteq √{1-R_ {p}^2/R_ {e}^2} as a potential scenario to dynamically put to the test certain post-Keplerian effects of both Newtonian and post-Newtonian nature. We numerically produce time series of the perturbations Δ ( δ τ ) of the Rømer-like, orbital component of the pulsar's time delay δ τ induced over 10 years by the pN gravitoelectric mass monopole ( {Schwarzschild}, GMc^{-2}) , quadrupole ( GMR^2_ {e}J_2 c^{-2}) , gravitomagnetic spin dipole ( {Lense}{-} {Thirring}, GSc^{-2}) and octupole ( GSR^2_ {e}ɛ ^2 c^{-2}) accelerations along with the Newtonian quadrupolar ( GMR^2_ {e}J_2) one. We do not deal with the various propagation time delays due to the travelling electromagnetic waves. It turns out that, for a Be-type star with M = 15 {M}_⊙ , R_ {e} = 5.96 {R}_⊙ , ν = 0.203, S = 3.41× 10^{45} {J} {s}, J_2 = 1.92× 10^{-3} orbited by a pulsar with an orbital period P_b∼ 40-70 days, the classical oblateness-driven effects are at the ≲ 4-150 {s} level, while the pN shifts are of the order of ≲ 1.5-20 {s} ( GMc^{-2}) , ≲ 10-40 {ms} ( GMR^2_ {e} J_2 c^{-2}) , ≲ 0.5-6 {ms} ( GSc^{-2}) , ≲ 5-20 μ {s} ( GSR^2_ {e}ɛ ^2 c^{-2}) , depending on their orbital configuration. The root-mean-square (rms) timing residuals σ_{τ } of almost all the existing non-recycled, non-millisecond pulsars orbiting massive, fast rotating main sequence stars are ≲ {ms}. Thus, such kind of binaries have the potential to become interesting laboratories to measure, or, at least, constrain, some Newtonian and post-Newtonian (GMc^{-2}, GMJ_2c^{-2}, and, perhaps, GSc^{-2} as well) key features of the distorted gravitational fields of the fast rotating stars hosted by them.
- Publication:
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European Physical Journal C
- Pub Date:
- August 2019
- DOI:
- 10.1140/epjc/s10052-019-7194-5
- arXiv:
- arXiv:1905.05514
- Bibcode:
- 2019EPJC...79..690I
- Keywords:
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- General Relativity and Quantum Cosmology;
- Astrophysics - Solar and Stellar Astrophysics;
- Physics - Space Physics
- E-Print:
- Latex2e, 24 pages, 5 figures, 3 tables. One affiliation corrected