Application of a two dipole model to PSR J1640-4631, a pulsar with an anomalous braking index

Abstract

Recent timing observation provides an intriguing result for the braking index of the X-ray pulsar PSR J1640-4631, which has a measured braking index $n=3.15\pm 0.03$. The decrease of the inclination angle between between the spin axis and the magnetic axis can be responsible for such a high braking index. However, the physical mechanisms causing the change of the magnetic inclination angle have not been fully understood. In this Letter, we apply a two-dipole model given by Hamil et al (2016) to explain the decrease of the magnetic inclination angle of PSR J1640-4631. The rotation effect of a charged sphere and the magnetization of ferromagnetically ordered material produce magnetic moments $M_1$ and $M_2$, respectively. There exist a minimum of the potential energy for the magnetic moment $M_2$ in the magnetic field of $M_1$, hence the $M_2$ will freely rotate around the minimum energy position (i. e equilibrium position), similar to a simple pendulum. Our calculation indicate the magnetic moment $M_2$ would evolve towards alignment with the spin axis for PSR J1640-4631, and cause the magnetic inclination angle to decrease. The single peak in the pulse profile favors a relatively low change rate of the magnetic inclination angle.

arXiv comment5 pages, 2 figures, PASJ in press

References in corpus (21)

• Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter
• Cooling neutron star in the Cassiopeia~A supernova remnant: Evidence for superfluidity in the core
• 45 Years of Rotation of the Crab Pulsar
• Direct Observation of the Cooling of the Cassiopeia A Neutron Star
• Evolution of the Magnetic Field Structure of the Crab Pulsar
• A High Braking Index for a Pulsar
• Constraining the Braking Indices of Magnetars
• The Dipole Magnetic Field and Spin-down Evolutions of The High Braking Index Pulsar PSR J1640-4631
• The population of pulsars with interpulses and the implications for beam evolution
• Hall drift and the braking indices of young pulsars
• NuSTAR Discovery of a Young, Energetic Pulsar Associated with the Luminous Gamma-ray Source HESS J1640-465
• Inclination angle and braking index evolution of pulsars with plasma-filled magnetosphere: application to high braking index of PSR J1640-4631
• Gravitational Waves from Pulsars and Their Braking Indices: The Role of a Time Dependent Magnetic Ellipticity
• Gravitational wave emission by the high braking index pulsar PSR J1640-4631
• Possible evolution of the pulsar braking index from larger than three to about one
• Evolution of the X-ray Profile of the Crab Pulsar
• Radiation from an off-centred rotating dipole in vacuum
• Braking Index of Isolated Pulsars II: A novel two-dipole model of pulsar magnetism
• The evolution of the magnetic inclination angle as an explanation of the long term red timing-noise of pulsars
• What can PSR J1640-4631 tell us about the internal physics of this neutron star?
• High braking index pulsar PSR J1640-4631: low-mass neutron star with a large inclination angle?

Cited by in corpus (1)

• Explaining high-braking indice of magnetars SGR 0501+4516 and 1E 2259+586 using the double magnetic-dipole model