Neutron Star Superfluidity, Dynamics and Precession

Basic rotational and magnetic properties of neutron superfluids and proton superconductors in neutron stars are reviewed. The modes of precession of the neutron superfluid are discussed in detail. We emphasize that at finite temperature, pinning of superfluid vortices does not offer any constraint on the precession. Any pinning energies can be surmounted by thermal activation and there exists a dynamical steady state in which the superfluid follows the precession of the crust at a small lag angle between the crust and superfluid rotation velocity vectors. At this small lag the system is far from the critical conditions for unpinning, even if the observed precession of the crust may entail a large angle between the figure axis and the crust's rotation velocity vector. We conclude that if long period modulations of pulse arrival times and pulse shapes observed in a pulsar like the PSR B1828-11 are due to the precession of the neutron star, this does not have any binding implications about the existence of pinning by flux lines or the existence of Type II superconductivity in the neutron star.Comment: 21 pages, one figure, to appear in the Proceedings of the NATO-ASI "The Electromagnetic Spectrum of Neutron Stars" held in Marmaris, Turkey, June 2004, eds. A. Baykal, S.K. Yerli, C. Inam and S. Grebene

Superfluid Spin-down, with Random Unpinning of the Vortices

The so-called ``creeping'' motion of the pinned vortices in a rotating superfluid involves ``random unpinning'' and ``vortex motion'' as two physically separate processes. We argue that such a creeping motion of the vortices need not be (biased) in the direction of an existing radial Magnus force, nor should a constant microscopic radial velocity be assigned to the vortex motion, in contradiction with the basic assumptions of the ``vortex creep'' model. We point out internal inconsistencies in the predictions of this model which arise due to this unjustified foundation that ignores the role of the actual torque on the superfluid. The proper spin-down rate of a pinned superfluid is then calculated and turns out to be much less than that suggested in the vortex creep model, hence being of even less observational significance for its possible application in explaining the post-glitch relaxations of the radio pulsars.Comment: To be published in J. Low Temp. Phys., Vol. 139, May 2005 [Eqs 11, 15-17 here, have been revised and, may be substituted for the corresponding ones in that paper

Dim Isolated Neutron Stars, Cooling and Energy Dissipation

The cooling and reheating histories of dim isolated neutron stars(DINs) are discussed. Energy dissipation due to dipole spindown with ordinary and magnetar fields, and due to torques from a fallback disk are considered as alternative sources of reheating which would set the temperature of the neutron star after the initial cooling era. Cooling or thermal ages are related to the numbers and formation rates of the DINs and therefore to their relations with other isolated neutron star populations. Interaction with a fallback disk, higher multipole fields and activity of the neutron star are briefly discussed.Comment: To appear in Astrophysics and Space Science, in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 2006; eds. D. Page, R. Turolla and S. Zane. Revised version: with minor change and typos correcte

Tkachenko waves, glitches and precession in neutron star

Here I discuss possible relations between free precession of neutron stars, Tkachenko waves inside them and glitches. I note that the proposed precession period of the isolated neutron star RX J0720.4-3125 (Haberl et al. 2006) is consistent with the period of Tkachenko waves for the spin period 8.4s. Based on a possible observation of a glitch in RX J0720.4-3125 (van Kerkwijk et al. 2007), I propose a simple model, in which long period precession is powered by Tkachenko waves generated by a glitch. The period of free precession, determined by a NS oblateness, should be equal to the standing Tkachenko wave period for effective energy transfer from the standing wave to the precession motion. A similar scenario can be applicable also in the case of the PSR B1828-11.Comment: 6 pages, no figures, accepted to Ap&S

Slowly Rotating General Relativistic Superfluid Neutron Stars with Relativistic Entrainment

Neutron stars that are cold enough should have two or more superfluids/supercondutors in their inner crusts and cores. The implication of superfluidity/superconductivity for equilibrium and dynamical neutron star states is that each individual particle species that forms a condensate must have its own, independent number density current and equation of motion that determines that current. An important consequence of the quasiparticle nature of each condensate is the so-called entrainment effect, i.e. the momentum of a condensate is a linear combination of its own current and those of the other condensates. We present here the first fully relativistic modelling of slowly rotating superfluid neutron stars with entrainment that is accurate to the second-order in the rotation rates. The stars consist of superfluid neutrons, superconducting protons, and a highly degenerate, relativistic gas of electrons. We use a relativistic $\sigma$ - $\omega$ mean field model for the equation of state of the matter and the entrainment. We determine the effect of a relative rotation between the neutrons and protons on a star's total mass, shape, and Kepler, mass-shedding limit.Comment: 30 pages, 10 figures, uses ReVTeX

On The Low Frequency Quasi Periodic Oscillations of X-ray Sources

Based on the interpretation of the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) to the Keplerian and the periastron precession frequencies at the magnetosphere-disk of X-ray neutron star (NS) respectively, we ascribe the low frequency Quasi Periodic Oscillations (LFQPO) and HBO (15-60 Hz QPO for Z sources or Atoll sources) to the periastron precession at some outer disk radius. The obtained conclusions include: all QPO frequencies increase with increasing the accretion rate. The obtained theoretical relations between HBO (LFQPO) frequency and the kHz QPO frequency are similar to the measured empirical formula. Further, the possible dynamical mechanism for QPO production is discussed.Comment: 6 pages, 2 figures, accepted by APSS, 200

Probing the Neutron Star Interior with Glitches

With the aim of constraining the structural properties of neutron stars and the equation of state of dense matter, we study sudden spin-ups, glitches, occurring in the Vela pulsar and in six other pulsars. We present evidence that glitches represent a self-regulating instability for which the star prepares over a waiting time. The angular momentum requirements of glitches in Vela indicate that at least 1.4% of the star's moment of inertia drives these events. If glitches originate in the liquid of the inner crust, Vela's `radiation radius' $R_\infty$ must exceed ~12 km for a mass of 1.4 solar masses. The isolated neutron star RX J18563-3754 is a promising candidate for a definitive radius measurement, and offers to further our understanding of dense matter and the origin of glitches.Comment: Invited talk at the Pacific Rim Conference on Stellar Astrophysics, Hong Kong, Aug. 1999. 9 pages, 5 figure

Covariant Vortex In Superconducting-Superfluid-Normal Fluid Mixtures with Stiff Equation of State

The integrals of motion for a cylindrically symmetric stationary vortex are obtained in a covariant description of a mixture of interacting superconductors, superfluids and normal fluids. The relevant integrated stress-energy coefficients for the vortex with respect to a vortex-free reference state are calculated in the approximation of a ``stiff'', i.e. least compressible, relativistic equation of state for the fluid mixture. As an illustration of the foregoing general results, we discuss their application to some of the well known examples of ``real'' superfluid and superconducting systems that are contained as special cases. These include Landau's two-fluid model, uncharged binary superfluid mixtures, rotating conventional superconductors and the superfluid neutron-proton-electron plasma in the outer core of neutron stars.Comment: 14 pages, uses RevTeX and amssymb, submitte

Magnetar-like X-Ray Bursts from a Rotation-powered Pulsar, PSR J1119-6127

Two energetic hard X-ray bursts have recently triggered the Fermi and Swift space observatories from the rotation powered pulsar, PSR J1119-6127. We have performed in depth spectral and temporal analyses of these two events. Our extensive searches in both observatory data for lower luminosity bursts uncovered 10 additional events from the source. We report here on the timing and energetics of the 12 bursts from PSR J1119-6127 during its burst active phase of 2016 July 26 and 28. We also found a spectral softer X-ray flux enhancement in a post burst episode, which shows evidence of cooling. We discuss here the implications of these results on the nature of this unusual high-field radio pulsar, which firmly place it within the typical magnetar population.Comment: Revised version, accepted for publication in ApJL. An expanded version of Table 1, as well as the light curves of all Fermi/GBM detected bursts can be found at http://magnetars.sabanciuniv.edu/psrj1119.ph