On Young Neutron Stars as Propellers and Accretors with Conventional Magnetic Fields

The similarity of rotation periods of, the anomalous X-ray pulsars (AXPs),the soft gamma ray repeaters (SGRs) and the dim thermal neutron stars (DTNs)suggests a common mechanism with an asymptotic spindown phase through thepropeller and early accretion stages. The DTNs are in the propeller stage.Their luminosities arise from frictional heating in the neutron star. If the8.4 s rotation period of the DTN RXJ 0720.4-3125 is close to its rotationalequilibrium period, the propeller torque indicates a magnetic field in the10$^{12}$ Gauss range. The mass inflow rate onto the propeller is of the orderof the AXP accretion rates. The limited range of rotation periods, taken to beclose to equilibrium periods, and magnetic fields in the range 5 E11- 5 E12Gauss correspond to mass inflow rates 3.2 E14 gm/s < \dot{M} < 4.2 E17 gm/s.Observed spindown rates of the AXPs and SGRs also fit in with these fieldsrather than magnetar fields periods. The source of the mass inflow is a remnantaccretion disk formed as part of the fallback during the supernova explosion.These classes of sources thus represent the alternative pathways for thoseneutron stars that do not become radio pulsars. For the highest mass inflowrates the propeller action may support enough circumstellar material so thatthe optical thickness to electron scattering destroys the X-ray beaming, andthe rotation period is not observable. These are the radio quiet neutron stars(RQNSs) at the centers of supernova remnants Cas A, Puppis A, RCW 103 and296.5+10.Comment: 28 pages, with one figure and one table. Submitted to Ap