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

The Effect of Quantized Magnetic Flux Lines on the Dynamics of Superfluid Neutron Star Cores

We investigate dynamical coupling timescales of a neutron star's superfluid core, taking into account the interactions of quantized neutron vortices with quantized flux lines of the proton superconductor in addition to the previously considered scattering of the charged components against the spontaneous magnetization of the neutron vortex line. We compare the cases where vortex motion is constrained in different ways by the array of magnetic flux tubes associated with superconducting protons. This includes absolute pinning to and creep across a uniform array of flux lines. The effect of a toroidal arrangement of flux lines is also considered. The inclusion of a uniform array of flux tubes in the neutron star core significantly decreases the timescale of coupling between the neutron and proton fluid constituents in all cases. For the toroidal component, creep response similar to that of the inner crust superfluid is possible.Comment: Submitted to MNRA

On the evolution of the radio pulsar PSR J1734−3333

Recent measurements showed that the period derivative of the ‘hig h-B’ radio pulsar PSR J1734−3333 is increasing with time. For neutron stars evolving with fallback disks, this rotational behavior is expected in certain phases of the long-term evolution. Using the same model as employed earlier to explain the evolution of anomalous X-ray pulsars and soft gamma-ray repeaters, we show that the period,the first and second period derivatives and the X-ray luminosity of this source can simultaneously acquire the observed values for a neutron star evolving with a fallback disk. We find that the required strength of the dipole field that can produce the source properties is in the range of 10^12 − 10^13 G on the pole of the neutron star. When the model source reaches the current state properties of PSR J1734−3333, accretion onto the star has not started yet, allowing the source to operate as a regular radio pulsar. Our results imply that PSR J1734−3333 is at an age of ∼3×10^4 −2×10^5years. Such sources will have properties like the X-ray dim isolated neutron stars or transient AXPs at a later epoch of weak accretion from the diminished fallback disk

Differences between the Two Anomalous X-Ray Pulsars: Variations in the Spin Down Rate of 1E 1048.1-5937 and An Extended Interval of Quiet Spin Down in 1E 2259+586

We analysed the RXTE archival data of 1E 1048.1-5937 covering a time span of more than one year. The spin down rate of this source decreases by 30 percent during the observation. We could not resolve the X-ray flux variations because of contamination by Eta Carinae. We find that the level of pulse frequency fluctuations of 1E 1048.1-5937 is consistent with typical noise levels of accretion powered pulsars. Recent RXTE observations of 1E 2259+586 have shown a constant spin down with a very low upper limit on timing noise. We used the RXTE archival X-ray observations of 1E 2259+586 to show that the intrinsic X-ray luminosity times series is also stable, with an rms fractional variation of less than 15 percent. The source could have been in a quiet phase of accretion with a constant X-ray luminosity and spin down rate.Comment: MNRAS in pres

Pulsar Braking Indices, Glitches and Energy Dissipation In Neutron Stars

Almost all pulsars with anomalous positive $\ddot \Omega$ measurements (corresponding to anomalous braking indices in the range 5$<n<$100), including all the pulsars with observed large glitches ($\Delta\Omega/\Omega$ $>$ 10$^{-7}$) as well as post glitch or interglitch $\ddot \Omega$ measurements obey the scaling between $\ddot \Omega$ and glitch parameters originally noted in the Vela pulsar. Negative second derivative values can be understood in terms of glitches that were missed or remained unresolved. We discuss the glitch rates and a priori probabilities of positive and negative braking indices according to the model developed for the Vela pulsar. This behavior supports the universal occurrence of a nonlinear dynamical coupling between the neutron star crust and an interior superfluid component. The implied lower limit to dynamical energy dissipation in a neutron star with spindown rate $\dot \Omega$ is $\dot E_{diss}> 1.7 \times 10 ^{-6} \dot E_{rot}$. Thermal luminosities and surface temperatures due to dynamical energy dissipation are estimated for old neutron stars which are spinning down as rotating magnetic dipoles beyond the pulsar death line.Comment: Accepted for publication in MNRA

On the outburst light curves of soft X-Ray transients as response of the accretion disk to mass deposition

We note that the solution of accretion disk dynamics for an initial delta-function mass distribution gives a light curve that fits both the rise and the decay pattern of the outburst light curves of black-hole soft X-ray transients (BSXTs) until the onset of the first mini outburst quite well. The Green's function solution of Lynden-Bell & Pringle (1974) is employed for two differenttime-independent viscosity laws to calculate the expected count rates of X-ray photons in the Ginga energy bands as a function of time. For both models basic characteristics of the outburst light curves of two typical sources GS 2000+25 and GS/GRS 1124-68 are reproduced together with plausible values of the thin disk parameter $\alpha$ and the recurrence times. This agreement with the outburst light curves and the source properties during quiescence support the idea of mass accumulation and the sporadic release of accumulated mass at the outer disk

The Peculiar Evolutionary History of IGR J17480-2446 in Terzan 5

The low mass X-ray binary (LMXB) IGR J17480-2446 in the globular cluster Terzan 5 harbors an 11 Hz accreting pulsar. This is the first object discovered in a globular cluster with a pulsar spinning at such low rate. The accreting pulsar is anomalous because its characteristics are very different from the other five known slow accreting pulsars in galactic LMXBs. Many features of the 11 Hz pulsar are instead very similar to those of accreting millisecond pulsars, spinning at frequencies >100 Hz. Understanding this anomaly is valuable because IGR J17480-2446 can be the only accreting pulsar discovered so far which is in the process of becoming an accreting millisecond pulsar. We first verify that the neutron star (NS) in IGR J17480-2446 is indeed spinning up by carefully analyzing X-ray data with coherent timing techniques that account for the presence of timing noise. We then study the present Roche lobe overflow epoch and the two previous spin-down epochs dominated by magneto dipole radiation and stellar wind accretion. We find that IGR J17480-2446 is very likely a mildly recycled pulsar and suggest that it has started a spin-up phase in an exceptionally recent time, that has lasted less than a few 10^7 yr. We also find that the total age of the binary is surprisingly low (<10^8 yr) when considering typical parameters for the newborn NS and propose different scenarios to explain this anomaly.Comment: Accepted by ApJ, in pres

Quasiperiodic oscillations in bright galactic-bulge X-ray sources

Quasiperiodic oscillations with frequencies in the range 5-50 Hz have recently been discovered in X-rays from two bright galactic-bulge sources and Sco X-1. These sources are weakly magnetic neutron stars accreting from disks which the plasma is clumped. The interaction of the magnetosphere with clumps in the inner disk causes oscillations in the X-ray flux with many of the properties observed

Damping of differential rotation in neutron stars

We derive the transport relaxation times for quasiparticle-vortex scattering processes via nuclear force, relevant for the damping of differential rotation of superfluids in the quantum liquid core of a neutron star. The proton scattering off the neutron vortices provides the dominant resistive force on the vortex lattice at all relevant temperatures in the phase where neutrons only are in the paired state. If protons are superconducting, a small fraction of hyperons and resonances in the normal state would be the dominant source of friction on neutron and proton vortex lattices at the core temperatures $T\ge 10^{7}$ K.Comment: 5 pages, Revtex, Phys. Rev. D 58, Rapid Communication, in pres