On the torque reversals of 4U 1626--67

Abstract

We have investigated the detailed torque-reversal behavior of 4U 1626--67 in the framework of the recently developed comprehensive model of the inner disk radius and torque calculations for neutron stars accreting from geometrically thin disks. The model can reproduce the torque -- X-ray luminosity relation across the torque reversals of 4U 1626--67. Our results imply that: (1) rotational equilibrium is reached when the inner disk radius equals the co-rotation radius, $r_{\mathrm{co}}$, while the conventional Alfven radius is greater than and close to $r_{\mathrm{co}}$, (2) both spin-up and spin-down torques are operating on either side of torque reversal, (3) with increasing accretion rate the spin-up torque associated with accretion onto the star gradually dominates the spin-down torque exerted by the disk. The torque reversals are the natural outcome of transitions between the well-defined weak-propeller and spin-up phases of the star with a stable geometrically thin accretion disk.

5 pages, 2 figures, accepted for publication in A&A

References in corpus (9)

• A Radio Pulsar/X-ray Binary Link
• "Propeller" Regime of Disk Accretion to Rapidly Rotating Stars
• Timing Observations of PSR J1023+0038 During a Low-Mass X-ray Binary State
• Transitional millisecond pulsars
• A broadband self-consistent modelling of the X-ray spectrum of 4U 1626--67
• Recent Torque Reversal of 4U 1907+09
• On the Torque Reversals of Accreting Neutron Stars
• Constraints on the disc-magnetosphere interaction in accreting pulsar 4U 1626--67
• Chandra/LETGS Studies of the Collisional Plasma in 4U 1626-67

Cited by in corpus (1)

• Tracking hidden magnetospheric fluctuations in accretion-powered pulsars with a Kalman filter