Asymmetric core combustion in neutron stars and a potential mechanism for gamma ray bursts

We study the transition of nuclear matter to strange quark matter (SQM) inside neutron stars (NSs). It is shown that the influence of the magnetic field expected to be present in NS interiors has a dramatic effect on the propagation of a laminar deflagration (widely studied so far), generating a strong acceleration of the flame in the polar direction. This results in a strong asymmetry in the geometry of the just formed core of hot SQM which resembles a cylinder orientated in the direction of the magnetic poles of the NS. This geometrical asymmetry gives rise to a bipolar emission of the thermal neutrino-antineutrino pairs produced in the process of SQM formation. The neutrino-antineutrino pairs annihilate into electron-positron pairs just above the polar caps of the NS giving rise to a relativistic fireball, thus providing a suitable form of energy transport and conversion to gamma emission that may be associated to short gamma ray bursts (GRBs).Comment: 2 figure

Strange Stars with a Density-Dependent Bag Parameter

We have studied strange quark stars in the framework of the MIT bag model, allowing the bag parameter B to depend on the density of the medium. We have also studied the effect of Cooper pairing among quarks, on the stellar structure. Comparison of these two effects shows that the former is generally more significant. We studied the resulting equation of state of the quark matter, stellar mass-radius relation, mass-central-density relation, radius-central-density relation, and the variation of the density as a function of the distance from the centre of the star. We found that the density-dependent B allows stars with larger masses and radii, due to stiffening of the equation of state. Interestingly, certain stellar configurations are found to be possible only if B depends on the density. We have also studied the effect of variation of the superconducting gap parameter on our results.Comment: 23 pages, 8 figs; v2: 25 pages, 9 figs, version to be published in Phys. Rev. (D

Solving relativistic hydrodynamic equation in presence of magnetic field for phase transition in a neutron star

Hadronic to quark matter phase transition may occur inside neutron stars (NS) having central densities of the order of 3-10 times normal nuclear matter saturation density ($n_0$). The transition is expected to be a two-step process; transition from hadronic to 2-flavour matter and two-flavour to $\beta$ equilibrated charge neutral three-flavour matter. In this paper we concentrate on the first step process and solve the relativistic hydrodynamic equations for the conversion front in presence of high magnetic field. Lorentz force due to magnetic field is included in the energy momentum tensor by averaging over the polar angles. We find that for an initial dipole configuration of the magnetic field with a sufficiently high value at the surface, velocity of the front increases considerably.Comment: 16 pages, 4 figures, same as published version of JPG, J. Phys. G: Nucl. Part. Phys. 39 (2012) 09520

Color-flavor locked strange matter

We analyze how the CFL states in dense matter work in the direction of enhancing the parameter space for absolutely stable phases (strange matter). We find that the "CFL strange matter" phase can be the true ground state of hadronic matter for a much wider range of the parameters of the model (the gap of the QCD Cooper pairs $\Delta$, the strange quark mass $m_s$ and the Bag Constant $B$) than the state without any pairing, and derive a full equation of state and an accurate analytic approximation to the lowest order in $\Delta$ and $m_{s}$ which may be directly used for applications. The effects of pairing on the equation of state are found to be small (as previously expected) but not negligible and may be relevant for astrophysics.Comment: 5 pages, 2 figure

Особливості розв’язку задач параметричної ідентифікації динамічних систем в умовах інтервальної невизначеності

Розглянуто задачу параметричної ідентифікації лінійних динамічних систем методами аналізу інтервальних даних. Показано, що у випадку врахування початкових інтервальних наближень дискретних значень прогнозованої характеристики дана задача є задачею розв’язування інтервальної системи нелінійних алгебричних рівнянь. Досліджено особливості формування та властивості розв’язку таких систем.Рассмотрена задача параметрической идентификации линейных динамических систем методами анализа интервальных данных. Показано, что в случае учета начальных интервальных приближений дискретных значений прогнозированной характеристики, данная задача есть задачей решения интервальной системы нелинейных алгебраических уравнений; исследованы особенности формирования и свойства решения таких систем.The problem of parameter identification of linear dynamic systems by methods of analysis of interval data is considered. It is shown that in the case of taking into account the initial interval approximations of discrete values of the predicted characteristics, this problem is the problem of solving interval system of nonlinear algebraic equations

Fall-back crust around a quark-nova compact remnant I: The degenerate shell case with applications to SGRs, AXPs and XDINs

We explore the formation and evolution of debris ejected around quark stars in the Quark Nova scenario, and the application to Soft Gamma-ray Repeaters (SGRs) and Anomolous X-ray Pulsars (AXPs). If an isolated neutron star explodes as a Quark Nova, an Iron-rich shell of degenerate matter forms out of the fall-back (crust) material. Our model can account for many of the observed features of SGRs and AXPs such as: (i) the two types of bursts (giant and regular); (ii) the spin-up and spin-down episodes during and following the bursts with associated persistant increases in $\dot{P}$; (iii) the energetics of the boxing day burst, SGR1806$+$20; (iv) the presence of an Iron line as observed in SGR1900$+$14; (v) the correlation between the far-Infrared and the X-ray fluxes during the bursting episode and the quiescent phase; (vi) the hard X-ray component observed in SGRs during the giant bursts, and (vii) the discrepancy between the ages of SGRs/AXPs and their supernova remnants. We also find a natural evolutionary relationship between SGRs and AXPs in our model which predicts that only the youngest SGRs/AXPs are most likely to exhibit strong bursting. Many features of X-ray Dim Isolated Neutron stars (XDINs) are also accounted for in our model such as, (i) the two-component blackbody spectra; (ii) the absorption lines around 300 eV; and (iii) the excess optical emission.Comment: submitted to Ap