Brian Niebergal

Numerical simulation of the hydrodynamical combustion to strange quark matter

We present results from a numerical solution to the burning of neutron matter inside a cold neutron star into stable u,d,s quark matter. Our method solves hydrodynamical flow equations in one dimension with neutrino emission from weak equilibrating reactions, and strange quark diffusion across the burning front. We also include entropy change from heat released in forming the stable quark phase. Our numerical results suggest burning front laminar speeds of 0.002-0.04 times the speed of light, much faster than previous estimates derived using only a reactive-diffusive description. Analytic solutions to hydrodynamical jump conditions with a temperature-dependent equation of state agree very well with our numerical findings for fluid velocities. The most important effect of neutrino cooling is that the conversion front stalls at lower density (below {approx_equal}2 times saturation density). In a two-dimensional setting, such rapid speeds and neutrino cooling may allow for a flame wrinkle instability to develop, possibly leading to detonation.

Quark-nova remnants - I. The leftover debris 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 ironrich shell of degenerate matter forms from its crust. This 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 increases in u 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 the youngest SGRs/AXPs are the 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.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

Magnetic Field Decay and Period Evolution of Anomalous X-Ray Pulsarsin the Context of Quark Stars

\dot{P}

Three-dimensional simulations of the reorganization of a quark star's magnetic field as induced by the meissner effect

; (iii) the energetics of the boxing day burst, SGR1806

Quark-Nova Explosion inside a Collapsar: Application to Gamma Ray Bursts

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Quark-nova remnants - II. The degenerate torus case with applications to AXPs

20; (iv) the presence of an Iron line as observed in SGR1900

SGR 0418+5729 as an evolved Quark-Nova compact remnant

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Gamma-ray burst engine activity within the quark nova scenario: prompt emission, X-ray plateau and sharp drop-off

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.

SGRs and AXPs proposed as ancestors of the Magnificent Seven

We discuss a model wherein soft gamma-ray repeaters (SGRs), anomalous X-ray pulsars (AXPs), and radio-quiet isolated neutron stars (RQINSs) are all compact objects exhibiting superconductivity, namely, color-flavor-locked quark stars. In particular, we calculate the magnetic field decay due to the expulsion of spin-induced vortices from the stars superfluid-superconducting interior, and the resultant spin-down rate. We find that for initial parameters characteristic of AXPs/SGRs (1013 G < B < 1014 G, 3 s < P < 12 s), the magnetic field strengths and periods remain unchanged within a factor of 2 for timescales on the order of 5 × 105 to 5 × 107 yr given a quark star of radius 10 km. Within these timescales, we show that the observed period clustering in RQINSs can be explained by compactness, and we calculate how the magnetic field and period evolve in a manner concurrent with RQINS observations.

Quark-nova remnants IV. Application to radio emitting anomalous X-ray pulsars transients

In a previous paper (Ouyed et al. 2004) we presented a new model for soft gamma-ray repeaters (SGR), based on the onset of colour superconductivity in quark stars. In this model, the bursts result from the reorganization of the exterior magnetic field following the formation of vortices that confine the internal magnetic field (the Meissner effect). Here we extend the model by presenting full 3-dimensional simulations of the evolution of the inclined exterior magnetic field immediately following vortex formation. The simulations capture the violent reconnection events in the entangled surface magnetic field as it evolves into a smooth, more stable, configuration which consists of a dipole field aligned with the star’s rotation axis. The total magnetic energy dissipated in this process is found to be of the order of 10 44 erg and, if it is emitted as synchrotron radiation, peaks typically at 280keV. The intensity decays temporally in a way resembling SGRs and AXPs (anomalous X-ray pulsars), with a tail lasting from a few to a few hundred times the rotation period of the star, depending on the initial inclination between the rotation and dipole axis. One of the obvious consequences of our model’s final state (aligned rotator) is the suppression of radio-emission in SGRs and AXPs following their bursting era. We suggest that magnetar-like magnetic field strength alone cannot be responsible for the properties of SGRs and AXPs, while a quark star entering the “Meissner phase” is compatible with the observational facts. We compare our model to observations and highlight our predictions.