Propeller vs. Magnetar Concepts for SGR/AXPs

Abstract

Two lines of thought exist as to the nature of Soft Gamma-ray Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs). On the one hand,we have neutron stars with super-critical magnetic fields, which spin-down the stars and power the gamma-ray bursts. On the other hand, are neutron stars with typical pulsar magnetic fields, which are spun-down by magnetospheric ``propeller'' torques from fallback or fossil disks in addition to magnetic dipole radiation. Many observational facts are available for comparing and contrasting these two concepts. The facts are described and whether or not each is compatible with these concepts is presented.