Ruling out Kozai resonance in highly eccentric galactic binary millisecond pulsar PSR J1903+0327

TL;DR

This study rules out the Kozai resonance as a formation mechanism for the highly eccentric binary millisecond pulsar PSR J1903+0327 by analyzing orbital eccentricity changes and comparing them with observations.

Contribution

The paper provides a detailed numerical analysis demonstrating that Kozai resonance cannot explain the observed orbital eccentricity of PSR J1903+0327, challenging previous formation hypotheses.

Findings

Orbital eccentricity should decrease if Kozai resonance is active.

Estimated eccentricity changes are much larger than observed.

Kozai resonance scenario is ruled out for PSR J1903+0327.

Abstract

We investigate the observational signatures associated with one of the proposed formation scenario for the recently discovered highly eccentric binary millisecond pulsar (MSP) PSR J1903+0327 in the galactic plane. The scenario requires that the MSP to be part of a hierarchical triple (HT), consisting of inner and outer binaries, experiencing the Kozai resonance. Numerical modeling of a bound point mass HT, while incorporating the effects due to the quadrupolar interactions between the binary orbits and dominant contributions to the general relativistic periastron precession in the inner binary, reveals that, at the present epoch, the orbital eccentricity of the binary MSP should decrease for reasonable ranges in the HT parameters. The estimated decrements in the orbital eccentricity of the inner binary are few parts in $10^{5}$, substantially higher than the reported accuracies in the estimation of the orbital eccentricity of the binary MSP, while employing various general relativistic timing models for isolated binary pulsars. For wide ranges in the allowed orbital parameters, the estimated rate of change in the eccentricity of the inner binary is orders of magnitude higher than the value recently measured by the pulsar timing analysis. Therefore, we rule out the scenario that the MSP is part of a HT undergoing the Kozai oscillations. The origin of this system in a typical globular cluster is also shown to be less likely than inferred in the discovery paper.