Chemical Evolution of Strongly Magnetized Quark Core in a Newborn Neutron Star

The chemical evolution of nascent quark matter core in a newborn compact neutron star is studied in presence of a strong magnetic field. The effective rate of strange quark production in degenerate quark matter core in presence of strong magnetic fields is obtained. The investigations show that in presence of strong magnetic fields a quark matter core becomes energetically unstable and hence a deconfinement transition to quark matter at the centre of a compact neutron star under such circumstances is not possible. The critical strength of magnetic field at the central core to make the system energetically unstable with respect to dense nuclear matter is found to be $\sim 4.4\times 10^{13}$G. This is the typical strength at which the Landau levels for electrons are populated. The other possible phase transitions at such high density and ultra strong magnetic field environment are discussed.Comment: 18 pages, latex, eight EPS figures not included, available under request, REVTEX forma

Electrical Conductivity at the Core of a Magnetar

An expression for the electrical conductivity at the core of a magnetar is derived using Boltzmann kinetic equation with the relaxation time approximation. The rates for the relevant scattering processes, e.g., electron-electron and electron-proton are evaluated in presence of strong quantizing magnetic fields using tree level diagrams. It is found that in presence of a strong quantizing magnetic field, electrical conductivity behaves like a second rank tensor. However, if the zeroth Landau levels are only occupied by the charged particles, it again behaves like a scaler of a one dimensional system.Comment: REVTEX File, 4 .eps figures (included

Symmetry group analysis of an ideal plastic flow

In this paper, we study the Lie point symmetry group of a system describing an ideal plastic plane flow in two dimensions in order to find analytical solutions. The infinitesimal generators that span the Lie algebra for this system are obtained. We completely classify the subalgebras of up to codimension two in conjugacy classes under the action of the symmetry group. Based on invariant forms, we use Ansatzes to compute symmetry reductions in such a way that the obtained solutions cover simultaneously many invariant and partially invariant solutions. We calculate solutions of the algebraic, trigonometric, inverse trigonometric and elliptic type. Some solutions depending on one or two arbitrary functions of one variable have also been found. In some cases, the shape of a potentially feasible extrusion die corresponding to the solution is deduced. These tools could be used to thin, curve, undulate or shape a ring in an ideal plastic material

A NuSTAR observation of disk reflection from close to the neutron star in 4U 1608-52

Studying the reflection of X-rays off the inner edge of the accretion disk in a neutron star low-mass X-ray binary, allows us to investigate the accretion geometry and to constrain the radius of the neutron star. We report on a NuSTAR observation of 4U 1608-52 obtained during a faint outburst in 2014 when the neutron star, which has a known spin frequency of 620 Hz, was accreting at ~1-2% of the Eddington limit. The 3-79 keV continuum emission was dominated by a Gamma~2 power law, with a ~1-2% contribution from a kTbb~0.3-0.6 keV black body component. The high-quality NuSTAR spectrum reveals the hallmarks of disk reflection; a broad iron line peaking near 7~keV and a Compton back-scattering hump around ~20-30 keV. Modeling the disk reflection spectrum points to a binary inclination of i~30-40 degrees and a small `coronal' height of h<8.5 GM/c2. Furthermore, our spectral analysis suggests that the inner disk radius extended to Rin~7-10 GM/c2, close to the innermost stable circular obit. This constrains the neutron star radius to R<21 km and the redshift from the stellar surface to z>0.12, for a mass of M=1.5 Msun and a spin parameter of a=0.29.Comment: 5 pages, 4 figures, 1 table, MNRAS Letters in pres

Mass formulas and thermodynamic treatment in the mass-density-dependent model of strange quark matter

The previous treatments for strange quark matter in the quark mass-density-dependent model have unreasonable vacuum limits. We provide a method to obtain the quark mass parametrizations and give a self-consistent thermodynamic treatment which includes the MIT bag model as an extreme. In this treatment, strange quark matter in bulk still has the possibility of absolute stability. However, the lower density behavior of the sound velocity is opposite to previous findings.Comment: Formatted in REVTeX 3.1, 5 pages, 3 figures, to appear in PRC6

Chiral Properties of QCD Vacuum in Magnetars- A Nambu-Jona-Lasinio Model with Semi-Classical Approximation

The breaking of chiral symmetry of light quarks at zero temperature in presence of strong quantizing magnetic fiels is studied using Nambu-Jona-Lasinio (NJL) model with Thomas-Fermi type semi-classical formalism. It is found that the dynamically generated light quark mass can never become zero if the Landau levels are populated and the mass increases with the increase of magnetic field strength.Comment: REVTEX 11 Pages, One .eps figure (included

X-Ray Spectroscopy of the Low-Mass X-ray Binaries 2S 0918-549 and 4U1543-624: Evidence for Neon-Rich Degenerate Donors

We present high-resolution spectroscopy of the neutron-star/low-mass X-ray binaries 2S 0918-549 and 4U 1543-624 with the High Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory and the Reflection Grating Spectrometer onboard XMM-Newton. Previous low-resolution spectra of both sources showed a broad line-like feature at 0.7 keV that was originally attributed to unresolved line emission. We recently showed that this feature could also be due to excess neutral Ne absorption, and this is confirmed by the new high-resolution Chandra spectra. The Chandra spectra are each well fit by an absorbed power-law + blackbody model with a modified Ne/O number ratio of 0.52+/-0.12 for 2S 0918-549 and 1.5+/-0.3 for 4U 1543-624, compared to the interstellar-medium value of 0.18. The XMM spectrum of 2S 0918-549 is best fit by an absorbed power-law model with a Ne/O number ratio of 0.46+/-0.03, consistent with the Chandra result. On the other hand, the XMM spectrum of 4U 1543-624 is softer and less luminous than the Chandra spectrum and has a best-fit Ne/O number ratio of 0.54+/-0.03. The difference between the measured abundances and the expected interstellar ratio, as well as the variation of the column densities of O and Ne in 4U 1543-624, supports the suggestion that there is absorption local to these binaries. We propose that the variations in the O and Ne column densities of 4U 1543-624 are caused by changes in the ionization structure of the local absorbing material. It is important to understand the effect of ionization on the measured absorption columns before the abundance of the local material can be determined. This work supports our earlier suggestion that 2S 0918-549 and 4U 1543-624 are ultracompact binaries with Ne-rich companions.Comment: 11 pages, 5 figures, major revisions including addition of XMM spectral analysis, accepted for publication in the Astrophysical Journal, vol. 59

Stability of strangelet at finite temperature

Using the quark mass density- and temperature dependent model, we have studied the thermodynamical properties and the stability of strangelet at finite temperature. The temperature, charge and strangeness dependences on the stability of strangelet are investigated. We find that the stable strangelets are only occured in the high strangeness and high negative charge region.Comment: 12 pages, 14 figure