First measurement of the total gravitational quadrupole moment of a black widow companion

Abstract

We present the first measurement of the gravitational quadrupole moment of the companion star of a spider pulsar, namely the black widow PSR J2051$-$0827. To this end we have re-analysed radio timing data using a new model which is able to account for periastron precession caused by tidal and centrifugal deformations of the star as well as by general relativity. The model allows for a time-varying component of the quadrupole moment, thus self-consistently accounting for the ill-understood orbital period variations observed in these systems. Our analysis results in the first detection of orbital precession in a spider system at $\dot{\omega }=-68.6_{-0.5}^{+0.9}$ deg/yr and the most accurate determination of orbital eccentricity for PSR J2051$-$0827 with $e=(4.2\pm 0.1)\times 10^{-5}$. We show that the variable quadrupole component is about 100 times smaller than the average quadrupole moment $\bar{Q}=-2.2_{-1}^{+0.6}\times 10^{41}$ kg.m${}^2$. We discuss how accurate modelling of high precision optical light curves of the companion star will allow its apsidal motion constant to be derived from our results.

MNRAS, in press

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Cited by in corpus (5)

• Einstein@Home Discovery of the Gamma-ray Millisecond Pulsar PSR J2039-5617 Confirms Its Predicted Redback Nature
• Multi-colour optical light curves of the companion star to the millisecond pulsar PSR J2051-0827
• A census of galactic spider binary millisecond pulsars with the Nançay Radio Telescope
• Timing Gamma-ray Pulsars using Gibbs Sampling
• Reconstruction of spider system's observables from orbital period modulations via the Applegate mechanism