Can the anomalous X-ray pulsars be powered by accretion?

Abstract

The nature of the 5-12 s "anomalous" X-ray pulsars remains a mystery. Among the models that have been proposed to explain the properties of AXPs, the most likely ones are: (1) isolated accreting neutron stars evolved from the Thorne-Żytkow objects due to complete spiral-in during the common envelope evolution of high-mass X-ray binaries, and (2) magnetars, which are neutron stars with ultra-high ($\sim 10^{14}-10^{15}$ G) surface magnetic fields. We have critically examined the predicted change of neutron star's spin in the accretion model, and found that it is unable to account for the steady spin-down observed in AXPs. A simple analysis also shows that any accretion disk around an isolated neutron star has extremely limited lifetime. A more promising explanation for such objects is the magnetar model.

9 pages, accepted for publication in ApJ

References in corpus (9)

• Discovery of a magnetar associated with the Soft Gamma Repeater SGR 1900+14
• X-ray irradiation in low mass binary systems
• The Discovery of an Anomalous X-ray Pulsar in the Supernova Remnant Kes 73
• Evidence for "Propeller" Effects In X-ray Pulsars GX 1+4 And GROJ1744-28
• On the Dramatic Spin-up/Spin-down Torque Reversals in Accreting Pulsars
• Spectral State Transitions in Aql X-1: Evidence for `Propeller' Effects
• Discovery of a 7 Second Anomalous X-ray Pulsar in the Distant Milky Way
• Warped Disks as a Possible Origin of Torque Reversals in Accretion-Powered Pulsars
• Deep IR and optical studies of the fields of 3 proposed TZO remnants

Cited by in corpus (7)

• On Young Neutron Stars as Propellers and Accretors with Conventional Magnetic Fields
• The Giant Flare of 1998 August 27 from SGR 1900+14: I. An Interpretive Study of BeppoSAX and Ulysses Observations
• Physical Mechanisms for the Variable Spin-down of SGR 1900+14
• Evidence of a cyclotron feature in the spectrum of the anomalous X-ray pulsar 1RXS J170849-400910
• Anomalous X-ray Pulsars and Soft gamma-ray Repeaters: Spectral Fits and the Magnetar Model
• Study of the Long Term Stability of two Anomalous X-ray Pulsars 4U 0142+61 and 1E 1048.1-5937 with ASCA
• On the Bimodal Spin Period Distribution of Be/X-ray Pulsars