1997/10/14 by Insu Yi, J. Craig Wheeler, J. C. Wheeler
Earth and Planetary Sciences · Physics and Astronomy · #Accretion (finance) #Astrophysical Phenomena and Observations #Astrophysics #Condensed matter physics #Galaxy #High-pressure geophysics and materials #Luminosity #Neutron star #Oscillation (cell signaling) #Physics #Pulsar #Pulsars and Gravitational Waves Research #Quantum mechanics #Spin (aerodynamics) #Spins #Torque #X-ray pulsar #astro-ph
paper · pdf · doi:10.1086/305592
11 pages, 2 figures, ApJ
arxiv created 1997/10/14 · openalex publication_date 1998/05/10 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The observed abrupt torque reversals in X-ray pulsars, 4U 1626-67, GX 1+4, and OAO 1657—415, can be explained by a transition in accretion-flow rotation from Keplerian to sub-Keplerian, which takes place at a critical accretion rate, ~10 16 -10 17 gs -1 . When a pulsar system spins up near equilibrium spin before the transition, the system goes into spin-down after transition to sub-Keplerian. If a system is well into the spin-up regime, the transition can cause a sharp decrease in spin-up rate but not a sudden spin-down. These observable types of abrupt torque change are distinguished from the smooth torque variation caused by a change of in the Keplerian flow. The observed abrupt torque reversal is expected when the pulsar magnetic field B * ~5 × 10 11 b −1/2 p L P 1/2 *,10 G, where the magnetic pitch parameter b p is of the order of a few, L x,36 is the X-ray luminosity in 10 36 ergs s -1 , and P *,10 is the pulsar spin period in 10 s. Observed quasi-periodic oscillation (QPO) periods tightly constrain the model. For 4U 1626-67, ≈ 2.7 × 10 16 g s -1 with b 1/2 p B * ≈ 2 × 10 12 G. We estimate ~6 × 10 16 g s -1 and b 1/2 p B * ~5 × 10 13 G for GX 1+4, and ~1 × 10 17 g s -1 and b 1/2 p B * ~2 × 10 13 G for OAO 1657-415. Reliable detection of QPOs before and after torque reversal could directly test the model. We discuss some outstanding uncertainties and difficulties in the present model.