Quasi Periodic Oscillations in Low Mass X-Ray Binaries and Constraints on the Equation of State of Neutron Star Matter

Recently discovered quasi periodic oscillations in the X-ray brightness of low mass X-ray binaries are used to derive constraints on the mass of the neutron star component and the equation of state of neutron star matter. The observations are compared with models of rapidly rotating neutron stars which are calculated by means of an exact numerical method in full relativity. For the equations of state we select a broad collection of models representing different assumptions about the many-body structure and the complexity of the composition of super dense matter. The mass constraints differ from their values in the approximate treatment by \sim 10%. Under the assumption that the maximum frequency of the quasi periodic oscillations originates from the innermost stable orbit the mass of the neutron star is in the range: $M\sim 1.92-2.25 M_\odot$. Especially the quasi periodic oscillation in the Atoll-source 4U 1820-30 is only consistent with equations of state which are rather stiff at high densities which is explainable, so far, only with pure nucleonic/leptonic composition. This interpretation contradicts the hypothesis that the protoneutron star formed in SN 1987A collapsed to a black hole, since this would demand a maximum neutron star mass below $1.6 M_\odot$. The recently suggested identification of quasi periodic oscillations with frequencies around 10 Hz with the Lense-Thirring precession of the accretion disk is found to be inconsistent with the models studied in this work, unless it is assumed that the first overtone of the precession is observed.Comment: 12 pages including figures, to be published in MNRA

Compatibility of neutron star masses and hyperon coupling constants

It is shown that the modern equations of state for neutron star matter based on microscopic calculations of symmetric and asymmetric nuclear matter are compatible with the lower bound on the maximum neutron-star mass for a certain range of hyperon coupling constants, which are constrained by the binding energies of hyperons in symmetric nuclear matter. The hyperons are included by means of the relativistic Hartree-- or Hartree--Fock approximation. The obtained couplings are also in satisfactory agreement with hypernuclei data in the relativistic Hartree scheme. Within the relativistic Hartree--Fock approximation hypernuclei have not been investigated so far.Comment: 12 pages, 3 figures. Dedicated to Prof. Georg Suessmann on the occasion of his 70th birthday. To be published in Zeitschrift fuer Naturforschung

Impact of internal heating on the thermal evolution of neutron stars

The impact of various competing heating processes on the thermal evolution of neutron stars is investigated. We show that internal heating leads to significantly enhanced surface temperatures for pulsars of middle and old age. The heating due to thermal creep of pinned vortices and due to outward motion of proton vortices in the interior of the star leads to a better agreement with the observed data in the case of enhanced cooling. The strong pinning models are ruled out by a comparison with the cooling data on the old pulsars. For millisecond pulsars, the heating due to thermal creep of pinned vortices and chemical heating of the core have the largest impact on the surface temperatures. The angular dependence of the heating rates require two dimensional cooling simulations in general. Such a simulation is performed for a selected case in order to check the applicability of one-dimensional codes used in the past.Comment: 18 pages, to be published in A & A. Postscript and additional tables at http://www.physik.uni-muenchen.de/sektion/suessmann/astro/cool/schaab.109

Energies of Quantum QED Flux Tubes

In this talk I present recent studies on vacuum polarization energies and energy densities induced by QED flux tubes. I focus on comparing three and four dimensional scenarios and the discussion of various approximation schemes in view of the exact treatment.Comment: 9 pages latex, Talk presented at the QFEXT 05 workshop in Barcelona, Sept. 2005. To appear in the proceeding

Near-BPS Skyrmions: Non-shell configurations and Coulomb effects

The relatively small binding energy in nuclei suggests that they may be well represented by near-BPS Skyrmions since their mass is roughly proportional to the baryon number $A.$ For that purpose, we propose a generalization of the Skyrme model with terms up to order six in derivatives of the pion fields and treat the nonlinear $\sigma$ and Skyrme terms as small perturbations. For our special choice of mass term (or potential) $V$, we obtain well-behaved analytical BPS-type solutions with non-shell configurations for the baryon density, as opposed to the more complex shell-like configurations found in most extensions of the Skyrme model . Along with static and (iso)rotational energies, we add to the mass of the nuclei the often neglected Coulomb energy and isospin breaking term. Fitting the four model parameters, we find a remarkable agreement for the binding energy per nucleon $B/A$ with respect to experimental data. These results support the idea that nuclei could be near-BPS Skyrmions.Comment: Correction of minors errors, references adde