On the bimodal magnetic field distribution of binary pulsars

We combine the idea of movement of magnetic flux tubes in the stellar interiors with the analysis of crustal physics of accreting neutron stars in low- and high-mass X-ray binaries to explain the bimodal magnetic field distribution of binary pulsars. We propose that this distribution may result from different crustal properties of neutron stars with different accretion rates and amounts of accreted matter. In addition, we may provide an explanation for why the magnetic field strengths of millisecond pulsars with low-mass companions saturate at ∼3 × 10 8 G when accreted mass exceeds ∼0.5 M ⊙. © 1997. The American Astronomical Society. All rights reserved.published_or_final_versio

Are soft γ-ray repeaters strange stars?

The soft γ-ray repeaters (SGRs) are proposed to result from young, magnetized strange stars with superconducting cores. As such a strange star spins down, the quantized vortex lines move outward and drag the magnetic flux tubes because of the strong coupling between them. Since the terminations of the tubes interact with the stellar crust, the dragged tubes can produce sufficient tension to crack the crust and pull parts of the broken platelet into the quark core. The deconfinement of crustal matter into strange quark matter will release energy. The model burst energy, duration, time interval, spectrum, and the persistent x-ray emission from SGRs are shown to be in agreement with observed results.published_or_final_versio

Gamma-ray production through inverse compton scattering with anisotropic photon field from accretion disk in AGNs

We give a detailed consideration of the photon spectrum produced by inverse Compton scattering off relativistic electrons in the anisotropic soft photon field from the accretion disk in jet model, assuming that the relativistic electrons and positrons are produced by collisions of relativistic protons with the soft photon and matter field. We considered soft photons from either the standard accretion disk or from the two-temperature accretion disk, respectively, which resulted in very different minimum Lorentz factors of the relativistic electrons and different scattered photon spectra. The scattered photon spectra seen from different angles and produced in various emission regions have been calculated for the different soft photon sources concerned and compared with results of other authors. The results of our calculations indicate that the instantaneous and stationary scattered photon spectra vary with the angle of scatter, the Lorentz factor of the jet, and the emission region of the γ-rays. Furthermore, whether X-rays and γ-rays can be produced cospatially depends upon the production mechanisms of the relativistic electrons. © 1997. The American Astronomical Society. All rights reserved.published_or_final_versio

The phase-resolved X-ray spectra of the Crab pulsar

We present a theoretical study of phase-dependent X-ray emission from the Crab pulsar. In the three-dimensional outer gap model for the Crab pulsar, X-ray emission is produced by synchrotron radiation of the secondary e ± pairs, which is sensitive to the local properties of the emission regions, i.e., local magnetic field strength and local number e ± density. We calculate X-ray pulse profiles for different energy bands and phase-dependent spectral indices of X-rays. We show that such a model can reproduce approximately the basic properties of the observed phase-dependent X-ray spectra of the Crab pulsar.published_or_final_versio

Approximate mass and radius formulas for static and rotating strange stars

Using the general relativistic conditions of thermodynamic equilibrium and fitting with values obtained from numerical integration of structure equations we derive approximate mass and radius formulas for static and uniformly rotating strange stars obeying the bag model equation of state. In the static case our formulas can reproduce the values of the mass and radius of the quark star with an error smaller than 1%. The maximum mass and radius of the strange stars can be predicted by fitting only one set of static configuration data. With the use of results obtained for the static configuration and with some supplementary assumptions about the behavior of the metric tensor at the center of the star, we can predict the rotational properties of maximally rotating strange stars within an error of 3%. From the approximate formulas we can derive the "empirical" formula relating the maximum rotation frequency of the uniformly rotating strange stars to the mass and radius of the maximum allowable static configuration. ©2000 The American Physical Society.published_or_final_versio

Time delay of photons of different energies in multidimensional cosmological models

We consider the general expressions for the time delay of photons of different energies in the framework of multidimensional cosmological models. In models with compactified extra dimensions (Kaluza-Klein-type models), the main source of the photon time delay is the time variation of the electromagnetic coupling due to dimensional reduction, which induces an energy dependence of the speed of light. A similar relation between the fine-structure constant and the multidimensional gauge couplings also appears in models with large (non-compactified) extra dimensions. For photons of energies around 1 TeV propagating at cosmological distances in an expanding universe, the time delay could range from a few seconds in the case of Kaluza-Klein models to a few days for models with large extra dimensions. As a consequence of the multidimensional effects, the intrinsic time profiles at the emitter rest frame differ from the detected time profiles. The formalism developed in the present paper allows the transformation of the predicted light curves of various energy ranges of the emitter into the frame of the observer for comparison with observations. Therefore, the study of the energy and redshift dependence of the time delay of photons emitted by astrophysical sources at cosmological distances could discriminate between the different multidimensional models and/or quantum gravity effects.published_or_final_versio

The Crab Optical/X/gamma-ray polarisation processes

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A three-dimensional model for the high-energy emissions from the Crab pulsar

We apply a three-dimensional outer gap accelerator model to the Crab pulsar for examining the light curve, phase-resolved spectrum and polarization. The curvature radiation process of the high-energy particles in the gap is calculated with an assumed three-dimensional structure of the accelerating electric field. We calculate the synchrotron self-inverse Compton process from the secondary pairs, which will be the observed emissions in optical to γ-ray regions. We compute radiation transfer for each radiated beam in three-dimensional geometry. © 2007 American Institute of Physics.published_or_final_versionThe 1st Glast Symposium, Stanford, CA., 5-8 February 2007. In AIP Conference Proceedings, 2007, v. 921, p. 423-42

The thermal response of A pulsar glitch: The nonspherically symmetric case

We study the thermal evolution of a pulsar after a glitch in which the energy is released from a relatively compact region. A set of relativistic thermal transport and energy balance equations is used to study the thermal evolution, without making the assumption of spherical symmetry. We use an exact cooling model to solve this set of differential equations. Our results could differ significantly from those obtained under the assumption of spherical symmetry. Even for young pulsars with a hot core like the Vela pulsar, a detectable hot spot could be observed after a glitch if a large amount of energy is released in a small region close to the surface of the star. The results suggest that the intensity variation and the relative phases of hard X-ray emissions in different epochs may provide important information on the equation of state. © 1998. The American Astronomical Society. All rights reserved.published_or_final_versio

Properties of nuclei in the inner crusts of neutron stars in the relativistic mean-field theory

We study the properties of nuclei in the inner crusts of neutron stars based on the Boguta-Bodmer nonlinear model in the relativistic mean-field theory. We carefully determine the surface diffuseness of the nuclei as the density of matter increases. The imaginary time step method is used to solve the Euler-Lagrange equation derived from the variational principle applied to the semiclassical energy density. It is shown that with increasing density, the spherical nuclei become more neutron rich and eventually merge to form a uniform liquid of neutrons, protons, and electrons. We find that the smaller the value of the incompressibility K, the lower the density at which the phase transition to uniform matter occurs. The relativistic extended Thomas-Fermi method is generalized to investigate nonspherical nuclei. Our results show that the spherical nucleus phase is the only equilibrium state in the inner crusts of neutron stars.published_or_final_versio