arXiv subjects

R. Ouyed

Publications and source records attributed to R. Ouyed.

At least 19 recordsLinked to original sources

arXiv2014

r-Java 2.0: the astrophysics

[Context:] This article is the second in a two part series introducing r-Java 2.0, a nucleosynthesis code for open use that performs r-process calculations and provides a suite of other analysis tools. [Aims:] The first paper discussed the nuclear physics inherent to r-Java 2.0 and in this article the astrophysics incorporated into the software will be detailed. [Methods:] R-Java 2.0 allows the user to specify the density and temperature evolution for an r-process simulation. Defining how the physical parameters (temperature and density) evolve can effectively simulate the astrophysical conditions for the r-process. Within r-Java 2.0 the user has the option to select astrophysical environments which have unique sets of input parameters available for the user to adjust. In this work we study three proposed r-process sites; neutrino-driven winds around a proto-neutron star, ejecta from a neutron star merger and ejecta from a quark nova. The underlying physics that define the temperature and density evolution for each site is described in this work. [Results:] In this paper a survey of the available parameters for each astrophysical site is undertaken and the effect on final r-process abundance is compared. The resulting abundances for each site are also compared to solar observations both independently and in concert. R-Java 2.0 is available for download from the website of the Quark-Nova Project: http://quarknova.ucalgary.ca/

astro-ph.IM↗

arXiv2014

r-Java 2.0: the nuclear physics

[Aims:] We present r-Java 2.0, a nucleosynthesis code for open use that performs r-process calculations as well as a suite of other analysis tools. [Methods:] Equipped with a straightforward graphical user interface, r-Java 2.0 is capable of; simulating nuclear statistical equilibrium (NSE), calculating r-process abundances for a wide range of input parameters and astrophysical environments, computing the mass fragmentation from neutron-induced fission as well as the study of individual nucleosynthesis processes. [Results:] In this paper we discuss enhancements made to this version of r-Java, paramount of which is the ability to solve the full reaction network. The sophisticated fission methodology incorporated into r-Java 2.0 which includes three fission channels (beta-delayed, neutron-induced and spontaneous fission) as well as computation of the mass fragmentation is compared to the upper limit on mass fission approximation. The effects of including beta-delayed neutron emission on r-process yield is studied. The role of coulomb interactions in NSE abundances is shown to be significant, supporting previous findings. A comparative analysis was undertaken during the development of r-Java 2.0 whereby we reproduced the results found in literature from three other r-process codes. This code is capable of simulating the physical environment of; the high-entropy wind around a proto-neutron star, the ejecta from a neutron star merger or the relativistic ejecta from a quark nova. As well the users of r-Java 2.0 are given the freedom to define a custom environment. This software provides an even platform for comparison of different proposed r-process sites and is available for download from the website of the Quark-Nova Project: http://quarknova.ucalgary.ca/

astro-ph.IM↗

arXiv2013

Double-humped Super-luminous Supernovae

Super-luminous supernova (SLSN) are supernovae showing extreme properties in their light-curves: high peak luminosities (more than 10 times brighter than bright SN Ia), and long durations. Several mechanisms have been proposed for SLSN, such as pair instability SN of a massive progenitor, interaction of the ejecta with a massive circumstellar shell, and the dual-shock quark nova (dsQN) model. The dual-shock quark nova model is unique in that it predicts a normal SN event will be seen about 10 days prior to the main SLSN event. The dsQN model is described here and shown that it is consistent with the light curve of the one currently known double-humped SLSN, 2006oz.

astro-ph.HE↗

arXiv2009

Quark-Novae, cosmic reionization, and early r-process element production

We examine the case for Quark-Novae (QNe) as possible sources for the reionization and early metal enrichment of the universe. Quark-Novae are predicted to arise from the explosive collapse (and conversion) of sufficiently massive neutron stars into quark stars. A Quark-Nova (QN) can occur over a range of time scales following the supernova event. For QNe that arise days to weeks after the supernovae, we show that dual-shock that arises as the QN ejecta encounter the supernova ejecta can produce enough photons to reionize hydrogen in most of the Inter-Galactic medium (IGM) by z ~ 6. Such events can explain the large optical depth tau_e ~ 0.1 as measured by WMAP, if the clumping factor, C, of the material being ionized is smaller than 10. We suggest a way in which a normal initial mass function (IMF) for the oldest stars can be reconciled with a large optical depth as well as the mean metallicity of the early IGM post reionization. We find that QN also make a contribution to r-process element abundances for atomic numbers A > 130. We predict that the main cosmological signatures of Quark-Novae are the gamma-ray bursts that announce their birth. These will be clustered at redshifts in the range z ~ 7-8 in our model.

astro-ph↗

arXiv2009

Three-Dimensional Simulations of Magnetized Superbubbles: New Insights into the Importance of MHD Effects on Observed Quantities

We present three-dimensional magnetohydrodynamic (MHD) simulations of superbubbles, to study the importance of MHD effects in the interpretation of images from recent surveys of the Galactic plane. These simulations focus mainly on atmospheres defined by an exponential density distribution and the Dickey & Lockman (1990) density distribution. In each case, the magnetic field is parallel to the Galactic plane and we investigate cases with either infinite scale height (constant magnetic field) or a constant ratio of gas pressure to magnetic pressure. The three-dimensional structure of superbubbles in these simulations is discussed with emphasis on the axial ratio of the cavity as a function of magnetic field strength and the age of the bubble. We investigate systematic errors in the age of the bubble and scale height of the surrounding medium that may be introduced by modeling the data with purely hydrodynamic models. Age estimates derived with symmetric hydrodynamic models fitted to an asymmetric magnetized superbubble can differ by up to a factor of four, depending on the direction of the line of sight. The scale height of the surrounding medium based on the Kompaneets model may be up to 50% lower than the actual scale height. We also present the first ever predictions of Faraday rotation by a magnetized superbubble based on three-dimensional MHD simulations. We emphasize the importance of MHD effects in the interpretation of observations of superbubbles.

astro-ph↗

arXiv2006

The Possibly Remnant Massive Outflow in G5.89-0.39: I - Observations and Initial MHD Simulations

We have obtained maps of the large scale outflow associated with the UCHII regionG5.89-0.39 in CO and 13CO (J=3-2), SiO (J=8-7,J=5-4), SO2 (13(2,12)-13(1,13)) and H13CO+(J=4-3). From these maps we have been able to determine the mass (3.3 M_sun), momentum (96 M_sun km/s), energy (3.5x10^{46} erg), mechanical luminosity (141 L_sun), and mass loss rate (~1x10^{-3}M_sun/yr) in the large scale outflow. The observationally derived parameters were used toguide 3D magnetohydrodynamic models of the jet entrained outflow. Through the combination of observations and simulations, we suggest that the large scale outflowmay be inclined by approximately 45 deg to the line of sight, and that the jet entraining the observed molecular outflow may have been active for as little as 1000 years, half the kinematic age of the outflow.

astro-ph↗

arXiv2005

Cooling of Quark Stars in the Color Superconductive Phase: Effect of Photons from Glueball decay

The cooling history of a quark star in the color superconductive phase is investigated. Here we specifically focus on the 2-flavour color (2SC) phase where novel process of photon generation via glueball (GLB) decay have been already investigated (Ouyed & Sannino 2001). The picture we present here can in principle be generalized to quark stars entering a superconductive phase where similar photon generation mechanisms are at play. As much as 10^{45}-10^{47} erg of energy is provided by the GLB decay in the 2SC phase. The generated photons slowly diffuse out of the quark star keeping it hot and radiating as a black-body (with possibly a Wien spectrum in gamma-rays) for millions of years. We discuss hot radio-quiet isolated neutron stars in our picture (such as RX J185635-3754 and RX J0720.4-3125) and argue that their nearly blackbody spectra (with a few broad features) and their remarkably tiny hydrogen atmosphere are indications that these might be quark stars in the color superconductive phase where some sort of photon generation mechanism (reminiscent of the GLB decay) has taken place. Fits to observed data of cooling compact stars favor models with superconductive gaps of Delta_2SC = 15-35 MeV and densities rho_2SC=(2.5-3.0)rho_N (rho_N being the nuclear matter saturation density) for quark matter in the 2SC phase. If correct, our model combined with more observations of isolated compact stars could provide vital information to studies of quark matter and its exotic phases.

astro-ph↗

arXiv2005

Fireballs from Quark Stars in the CFL Phase: Application to Gamma Ray Bursters

Recent studies of photon-generation mechanisms in the color-superconducting Color-Flavor Locked (CFL) phase of dense quark matter have found gamma-ray emissivities in excess of ~ 10^{50} erg cm^{-3} s^{-1} for temperatures in the 10-30 MeV range. We suggest that this property can trigger gamma-ray bursts (GRBs) and associated fireballs at the surface of hypothetical hot (newly born) quark stars with an energy release of up to 10^{48}-10^{50} erg within a fraction of a millisecond. If surrounded by an accretion disk following its formation, the star's bursting activity can last from tens of milliseconds to hundreds of seconds releasing up to 10^{52} erg in total energy. We discuss typical features of observed GRBs within our model and explain how quark stars in the CFL phase might constitute natural candidates for corresponding inner engines.

astro-ph↗

arXiv2005

Ultra-high energy cosmic rays from Quark Novae

We explore acceleration of ions in the Quark Nova (QN) scenario, where a neutron star experiences an explosive phase transition into a quark star (born in the propeller regime). In this picture, two cosmic ray components are isolated: one related to the randomized pulsar wind and the other to the propelled wind, both boosted by the ultra-relativistic Quark Nova shock. The latter component acquires energies $10^{15} {\rm eV} 10^{18.6}$ eV. The composition is dominated by ions present in the pulsar wind in the energy range above $10^{18.6}$ eV, while at energies below $10^{18}$ eV the propelled ejecta, consisting of the fall-back neutron star crust material from the explosion, is the dominant one. Added to these two components, the propeller injects relativistic particles with Lorentz factors $Γ_{\rm prop.} \sim 1-1000$, later to be accelerated by galactic supernova shocks. The QN model appears to be able to account for the extragalactic cosmic rays above the ankle and to contribute a few percent of the galactic cosmic rays below the ankle. We predict few hundred ultra-high energy cosmic ray events above $10^{19}$ eV for the Pierre Auger detector per distant QN, while some thousands are predicted for the proposed EUSO and OWL detectors.

astro-ph↗

arXiv2004

Meissner Effect and Vortex Dynamics in Quark Stars -- A Model for Soft Gamma-Ray Repeaters

We present a new model for soft gamma-ray repeaters based on a quark star born with temperatures above the critical value (T_c) for the onset of the colour-flavor locked superconductivity. The quark star then quickly cools below T_c, expelling a fraction of the surface magnetic field via the Meissner effect. We show that if a small fraction (\leq 10%) of the surface magnetic field (10^{14} - 10^{15} {\rm G}) is expelled, it quickly decays via magnetic reconnection and heats up the quark star surface to temperatures > 10^9 {\rm K}. Created (e^{+},e^{-}) pairs annihilate into gamma rays emitted in a giant burst (the first burst in our model), with a luminosity of \sim 10^{45} {\rm ergs} {\rm s}^{-1}. Subsequent bursts result from the restructuring of the surface magnetic field following the formation and relaxation of a vortex lattice which confines the internal magnetic field. During this phase, energy is sporadically released as a consequence of magnetic reconnection events in the entangled surface magnetic field as it evolves into a smooth, more stable, configuration. The star eventually enters a quiescent phase in which energy is continuously supplied by vortex annihilation at the surface. As the star spins down, the outermost vortex lines will be pushed to the surface where they annihilate and release their confined magnetic field. We show that the corresponding luminosity is L_v \sim 10^{36} {\rm ergs} {\rm s}^{-1} for a typical soft gamma-ray repeater spinning with a period of 8 {\rm s} and a surface magnetic field not exceeding 10^{15} {\rm G}. Our model can be applied to any situation where a T>T_{\rm c} quark star is generated. We discuss the connection between anomalous X-ray pulsars and soft gamma-ray repeaters in the context of our model.

astro-ph↗

arXiv2004

Photon Emission from Dense Quark Matter

Thermal emission rates and mean free paths of photons in a color-flavor locked (CFL) phase of quark matter at high densities and moderate temperatures are evaluated. Our calculations are based on a low-energy effective theory for CFL matter describing Goldstone boson excitations and their electromagnetic as well as strong interactions. In-medium coupling strengths of vector mesons are found to be smaller than in vacuum. As a consequence of in-medium modified pion dispersion relations, novel processes such as pi+ pi- -> gamma and gamma -> pi+ pi- become possible. The total photon emissivity is found to be very large, exceeding contributions from thermal e+ e- annihilation above temperatures of about 5 MeV. At the same time, the corresponding mean free paths become very small. Our results imply that the photon flux from the surface of a (hypothetical) CFL star in its early hot stages saturates the black-body limit. Estimates for the early thermal evolution of the star are also presented.

hep-ph↗

arXiv2003

Planets orbiting Quark Nova compact remnants

We explore planet formation in the Quark Nova scenario. If a millisecond pulsar explodes as a Quark Nova, a protoplanetary disk can be formed out of the metal rich fall-back material. The propeller mechanism transfers angular momentum from the born quark star to the disk that will go through viscous evolution with later plausible grain condensation and planet formation. As a result, earth-size planets on circular orbits may form within short radii from the central quark star. The planets in the PSR1257+12 system can be explained by our model if the Quark Nova compact remnant is born with a period of $\sim 0.5$ ms following the explosion. We suggest that a good portion of the Quark Nova remnants may harbour planetary systems.

astro-ph↗

arXiv2002

Quark-Nova

We explore the scenario where the core of a neutron star (having experienced a transition to an up and down quark phase) shrinks into the equilibrated quark object after reaching strange quark matter saturation density (where a composition of up, down and strange quarks is the favored state of matter). The overlaying (envelope) material free-falls following the core contraction releasing upto 10^{53} {\rm ergs} in energy as radiation, partly as a result of the conversion of envelope material to quarks. This phenomena, we named Quark-Nova, leads to a wide variety of ejectae ranging form the Newtonian, "dirty" to the ultra-relativistic fireball. The mass range of the corresponding compact remnant (the quark star) ranges from less than 0.3M_{\odot} up to a solar mass. We discuss the connection between Quark-Novae and Gamma ray bursts and suggest the recently studied GRB011211 event as a plausible Quark-Nova candidate.

astro-ph↗

arXiv2002

Three-Dimensional Simulations of Jets from Keplerian Disks: Self--Regulatory Stability

We present the extension of previous two-dimensional simulations of the time-dependent evolution of non-relativistic outflows from the surface of Keplerian accretion disks, to three dimensions. The accretion disk itself is taken to provide a set of fixed boundary conditions for the problem. The 3-D results are consistent with the theory of steady, axisymmetric, centrifugally driven disk winds up to the Alfvén surface of the outflow. Beyond the Alfvén surface however, the jet in 3-D becomes unstable to non-axisymmetric, Kelvin-Helmholtz instabilities. We show that jets maintain their long-term stability through a self-limiting process wherein the average Alfvénic Mach number within the jet is maintained to order unity. This is accomplished in at least two ways. First, poloidal magnetic field is concentrated along the central axis of the jet forming a ``backbone'' in which the Alfvén speed is sufficiently high to reduce the average jet Alfvénic Mach number to unity. Second, the onset of higher order Kelvin-Helmholtz ``flute'' modes (m \ge 2) reduce the efficiency with which the jet material is accelerated, and transfer kinetic energy of the outflow into the stretched, poloidal field lines of the distorted jet. This too has the effect of increasing the Alfvén speed, and thus reducing the Alfvénic Mach number. The jet is able to survive the onset of the more destructive m=1 mode in this way. Our simulations also show that jets can acquire corkscrew, or wobbling types of geometries in this relatively stable end-state, depending on the nature of the perturbations upon them. Finally, we suggest that jets go into alternating periods of low and high activity as the disappearance of unstable modes in the sub-Alfvénic regime enables another cycle of acceleration to super-Alfvénic speeds.

astro-ph↗

arXiv2002

Quark Stars as inner engines for Gamma Ray Bursts?

A model for Gamma ray bursts inner engine based on quark stars (speculated to exist in nature) is presented. We describe how and why these objects might constitute new candidates for GRB inner engines. At the heart of the model is the onset of exotic phases of quark matter at the surface of such stars, in particular the 2-flavor color superconductivity. A novel feature of such a phase is the generation of particles which are unstable to photon decay providing a natural mechanism for a fireball generation; an approach which is fundamentally different from models where the fireball is generated during collapse or conversion of neutron star to quark star processes. The model is capable of reproducing crucial features of Gamma ray bursts, such as the episodic activity of the engine (multiple and random shell emission) and the two distinct categories of the bursts (two regimes are isolated in the model with \sim 2 s and \sim 81 s burst total duration).

astro-ph↗

arXiv2002

Quark Stars and Color Superconductivity: A GRB connection ?

At this conference many interesting talks were presented on the plausible existence of Quark Stars. Other talks dealt with the exotic new phases of quark matter at very high density. Here, I show how combining these two elements might offer a new way of tackling the Gamma Ray Burst puzzle.

astro-ph↗

arXiv2001

Initial magnetic field configurations for 3-dimensional simulations of astrophysical jets

We solve, and provide analytical expressions, for current-free magnetic configurations in the context of initial setups of 3-dimensional simulations of astrophysical jets involving an accretion disk corona in hydrostatic balance around a central object. These configurations which thread through the accretion disk and its corona preserve the initial hydrostatic state. This work sets stage for future 3-dimensional jet simulations (including disk rotation and mass-load) where launching, acceleration and collimation mechanisms can be investigated.

astro-ph↗

arXiv2001

The Glueball sector of two-flavor Color Superconductivity

We construct the effective Lagrangian describing the light glueballs associated with the unbroken and confining SU(2) color subgroup for the 2 flavor superconductive phase of QCD. This Lagrangian constitutes a key ingredient for understanding the non perturbative physics of 2 flavor color superconductivity. We estimate the two photon decay process of the light glueballs using the saturation of the electromagnetic trace anomaly at the effective Lagrangian level. The present results are particularly relevant to our model of Gamma Ray Bursts based on color superconductivity in Quark Stars (R. Ouyed and F. Sannino astro-ph/0103022).

hep-ph↗