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 the propeller and early accretion stages. The DTNs are in the propeller stage. Their luminosities arise from frictional heating in the neutron star. If the 8.4 s rotation period of the DTN RXJ 0720.4-3125 is close to its rotational equilibrium period, the propeller torque indicates a magnetic field in the 10$^{12}$ Gauss range. The mass inflow rate onto the propeller is of the order of the AXP accretion rates. The limited range of rotation periods, taken to be close to equilibrium periods, and magnetic fields in the range 5 E11- 5 E12 Gauss 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 fields rather than magnetar fields periods. The source of the mass inflow is a remnant accretion disk formed as part of the fallback during the supernova explosion. These classes of sources thus represent the alternative pathways for those neutron stars that do not become radio pulsars. For the highest mass inflow rates the propeller action may support enough circumstellar material so that the optical thickness to electron scattering destroys the X-ray beaming, and the 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 and 296.5+10.Comment: 28 pages, with one figure and one table. Submitted to Ap

QPO frequency derivative - frequency correlation indicates non-Keplerian boundary layer with a maximum in rotation rate

The correlation between the frequency and the absolute value of the frequency derivative of the kilohertz QPOs observed for the first time from 4U 1636-53 is a simple consequence and indicator of the existence of a non-Keplerian rotation rate in the accretion disk boundary layer. This paper interprets the observed correlation, showing that the observations provide strong evidence in support of the fundamental assumption of disk accretion models around slow rotators, that the boundary layer matches the Keplerian disk to the neutron star magnetosphere.Comment: Accepted for publication in MNRAS Letter