arXiv subjects

Rachid Ouyed

Publications and source records attributed to Rachid Ouyed.

At least 55 records · Page 3Linked to original sources

arXiv2012

Quark nova imprint in the extreme supernova explosion SN 2006gy

The extremely luminous supernova 2006gy (SN 2006gy) is among the most energetic ever observed. The peak brightness was 100 times that of a typical supernova and it spent an unheard of 250 days at magnitude -19 or brighter. Efforts to describe SN 2006gy have pushed the boundaries of current supernova theory. In this work we aspire to simultaneously reproduce the photometric and spectroscopic observations of SN 2006gy using a quark nova model. This analysis considers the supernova explosion of a massive star followed days later by the quark nova detonation of a neutron star. We lay out a detailed model of the interaction between the supernova envelope and the quark nova ejecta paying special attention to a mixing region which forms at the inner edge of the supernova envelope. This model is then fit to photometric and spectroscopic observations of SN 2006gy. This QN model naturally describes several features of SN 2006gy including the late stage light curve plateau, the broad Hα line and the peculiar blue Hα absorption. We find that a progenitor mass between 20Msun and 40Msun provides ample energy to power SN 2006gy in the context of a QN.

astro-ph.HE↗

arXiv2012

Spindown of Isolated Neutron Stars: Gravitational Waves or Magnetic Braking?

We study the spindown of isolated neutron stars from initially rapid rotation rates, driven by two factors: (i) gravitational wave emission due to r-modes and (ii) magnetic braking. In the context of isolated neutron stars, we present the first study including self-consistently the magnetic damping of r-modes in the spin evolution. We track the spin evolution employing the RNS code, which accounts for the rotating structure of neutron stars for various equations of state. We find that, despite the strong damping due to the magnetic field, r-modes alter the braking rate from pure magnetic braking for B<10^{13}G. For realistic values of the saturation amplitude, the r-mode can also decrease the time to reach the threshold central density for quark deconfinement. Within a phenomenological model, we assess the gravitational waveform that would result from r-mode driven spindown of a magnetized neutron star. To contrast with the persistent signal during the spindown phase, we also present a preliminary estimate of the transient gravitational wave signal from an explosive quark-hadron phase transition, which can be a signal for the deconfinement of quarks inside neutron stars.

astro-ph.SR↗

arXiv2012

The peculiar case of the "double-humped" super-luminous supernova SN2006oz

SN2006oz is a super-luminous supernova with a mysterious bright precursor that has resisted explanation in standard models. However, such a precursor has been predicted in the dual-shock quark nova (dsQN) model of super-luminous supernovae -- the precursor is the SN event while the main light curve of the SLSN is powered by the Quark-Nova (QN; explosive transition of the neutron star to a quark star). As the SN is fading, the QN re-energizes the SN ejecta, producing a "double-humped" light curve. In this paper, we show the dsQN model successfully reproduces the observed light curve of SN2006oz.

astro-ph.HE↗

arXiv2011

Quark-Novae in Low-mass X-ray Binaries II: Application to G87-7 and to GRB 110328A

We propose a simple model explaining two outstanding astrophysical problems related to compact objects: (1) that of stars such as G87-7 (alias EG 50) that constitute a class of relatively low-mass white dwarfs which nevertheless fall away from the C/O composition and (2) that of GRB 110328A/Swift J164449.3+57345 which showed spectacularly long-lived strong X-ray flaring, posing a challenge to standard GRB models. We argue that both these observations may have an explanation within the unified framework of a Quark-Nova occurring in a low-mass X-ray binary (neutron star- white dwarf). For LMXBs where the binary separation is sufficiently tight, ejecta from the exploding Neutron Star triggers nuclear burning in the white dwarf on impact, possibly leading to Fe-rich composition compact white dwarfs with mass 0.43M_sun < M_WD < 0.72M_sun, reminiscent of G87-7. Our results rely on the assumption, which ultimately needs to be tested by hydrodynamic and nucleosynthesis simulations, that under certain circumstances the WD can avoid the thermonuclear runaway. For heavier white dwarfs (i.e. M_WD > 0.72M_sun) experiencing the QN shock, degeneracy will not be lifted when Carbon burning begins, and a sub-Chandrasekhar Type Ia Supernovae may result in our model. Under slightly different conditions, and for pure He white dwarfs (i.e. M_WD < 0.43M_sun), the white dwarf is ablated and its ashes raining down on the Quark star leads to accretion-driven X-ray luminosity with energetics and duration reminiscent of GRB 110328A. We predict additional flaring activity towards the end of the accretion phase if the Quark star turns into a Black Hole.

astro-ph.HE↗

arXiv2011

A Spallation Model for the Titanium-rich Supernova Remnant Cassiopeia A

Titanium-rich subluminous supernovae are rare and challenge current SN nucleosynthesis models. We present a model in which ejecta from a standard Supernova is impacted by a second explosion of the neutron star (a Quark-nova), resulting in spallation reactions that lead to 56Ni destruction and 44Ti creation under the right conditions. Basic calculations of the spallation products shows that a delay between the two explosions of ~ 5 days reproduces the observed abundance of 44Ti in Cas A and explains its low luminosity as a result of the destruction of 56Ni. Our results could have important implications for lightcurves of subluminous as well as superluminous supernovae.

astro-ph.HE↗

arXiv2011

r-Java : An r-process Code and Graphical User Interface for Heavy-Element Nucleosynthesis

We present r-Java, an r-process code for open use, that performs r-process nucleosynthesis calculations. Equipped with a simple graphical user interface, r-Java is capable of carrying out nuclear statistical equilibrium (NSE) as well as static and dynamic r-process calculations for a wide range of input parameters. In this introductory paper, we present the motivation and details behind r-Java, and results from our static and dynamic simulations. Static simulations are explored for a range of neutron irradiation and temperatures. Dynamic simulations are studied with a parameterized expansion formula. Our code generates the resulting abundance pattern based on a general entropy expression that can be applied to degenerate as well as non-degenerate matter, allowing us to track the rapid density and temperature evolution of the ejecta during the initial stages of ejecta expansion. At present, our calculations are limited to the waiting-point approximation. We encourage the nuclear astrophysics community to provide feedback on the code and related documentation, which is available for download from the website of the Quark-Nova Project: http://quarknova.ucalgary.ca/

nucl-th↗

arXiv2011

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

Soft gamma repeaters and anomalous X-ray pulsars are believed to be magnetars, i.e. neutron stars powered by extreme magnetic fields, B~10^(14)-10^(15) Gauss. The recent discovery of a soft gamma repeater with low magnetic field (< 7.5x10^(12) Gauss), SGR 0418+5729, which shows bursts similar to those of SGRs, implies that a high surface dipolar magnetic field might not be necessary for magnetar-like activity. We show that the quiescent and bursting properties of SGR 0418+5729 find natural explanations in the context of low-magnetic field Quark-Nova (detonative transition from a neutron star to a quark star) remnants, i.e. an old quark star surrounded by degenerate (iron-rich) Keplerian ring/debris ejected during the Quark-Nova explosion. We find that a 16 Myr old quark star surrounded by a ~ 10^(-10)xM_sun ring, extending in radius from ~ 30 km to 60 km, reproduces many observed properties of SGR 0418+5729. The SGR-like burst is caused by magnetic penetration of the inner part of the ring and subsequent accretion. Radiation feedback results in months-long accretion from the ring's non-degenerate atmosphere which matches well the observed decay phase. We make specific predictions (such as an accretion glitch of Delta P/P ~ - 2x10^(-11) during burst and a sub-keV proton cyclotron line from the ring) that can be tested by sensitive observations.

astro-ph.HE↗

arXiv2011

Quark-Novae in Low-Mass X-ray Binaries with massive neutron stars: A universal model for short-hard Gamma-Ray Bursts

We show that several features reminiscent of short-hard Gamma-ray Bursts (GRBs) arise naturally when Quark-Novae occur in low-mass X-ray binaries born with massive neutron stars (> 1.6M_sun) and harboring a circumbinary disk. Near the end of the first accretion phase, conditions are just right for the explosive conversion of the neutron star to a quark star (Quark-Nova). In our model, the subsequent interaction of material from the neutron star's ejected crust with the circumbinary disk explains the duration, variability and near-universal nature of the prompt emission in short-hard GRBs. We also describe a statistical approach to ejecta break-up and collision to obtain the photon spectrum in our model, which turns out remarkably similar to the empirical Band function (Band 1993). We apply the model to the fluence and spectrum of GRB 000727, GRB 000218, and GRB980706A obtaining excellent fits. Extended emission (spectrum and duration) is explained by shock-heating and ablation of the white dwarf by the highly energetic ejecta. Depending on the orbital separation when the Quark-Nova occurs, we isolate interesting regimes within our model when both prompt and extended emission can occur. We find that the spectrum can carry signatures typical of Type Ib/c SNe although these should appear less luminous than normal type Ib/c SNe. Late X-ray activity is due to accretion onto the quark star as well as its spin-down luminosity. Afterglow activity arise from the expanding shell of material from the shock-heated expanding circumbinary disk. We find a correlation between the duration and spectrum of short-hard GRBs as well as modest hard-to-soft time evolution of the peak energy.

astro-ph.HE↗

arXiv2010

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 1D with neutrino emission from weak equilibrating reactions, and strange quark diffusion across the burning front. We also include entropy change due to 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 approximately 2 times saturation density). In a 2-dimensional setting, such rapid speeds and neutrino cooling may allow for a flame wrinkle instability to develop, possibly leading to detonation.

nucl-th↗

arXiv2010

Confronting 3 Dimensional Time-dependent Jet Simulations with HST Observations

We perform state-of-the-art, 3D, time-dependent simulations of magnetized disk winds, carried out to simulation scales of 60 Astronomical Units, in order to confront optical HST observations of protostellar jets. We ``observe'' the optical forbidden line emission produced by shocks within our simulated jets and compare these with actual observations. Our simulations reproduce the rich structure of time varying jets, including jet rotation far from the source, an inner (up to 400 km/s) and outer (less than 100 km/s) component of the jet, and jet widths of up to 20 Astronomical Units in agreement with observed jets. These simulations when compared with the data are able to constrain disk wind models. In particular, models featuring a disk magnetic field with a modest radial spatial variation across the disk are favored.

astro-ph.SR↗

arXiv2010

Vortex Dynamics in Color-Superconducting Quark stars: The Re-heating of Magnetars

Compact stars made of quark matter rather than confined hadronic matter, are expected to form a color superconductor. This superconductor ought to be threaded with rotational vortex lines within which the star's interior magnetic field is confined. The vortices (and thus magnetic flux) would be expelled from the star during stellar spin-down, leading to magnetic reconnection at the surface of the star and the prolific production of thermal energy. In this Letter, we show that this energy release can re-heat quark stars to exceptionally high temperatures, such as observed for Soft Gamma Repeaters (SGRs), Anomalous X-Ray pulsars (AXPs), and X-ray dim isolated neutron stars (XDINs). Moreover, our numerical investigations of the temperature evolution, spin-down rate, and magnetic field behavior of such superconducting quark stars suggest that SGRs, AXPs, and XDINs may be linked ancestrally. Finally, we discuss the possibility of a time delay before the star enters the color superconducting phase, which can be used to estimate the density at which quarks deconfine. We find this density to be five times that of nuclear saturation.

astro-ph.HE↗

arXiv2010

Student's t-Distribution Based Option Sensitivities: Greeks for the Gosset Formulae

European options can be priced when returns follow a Student's t-distribution, provided that the asset is capped in value or the distribution is truncated. We call pricing of options using a log Student's t-distribution a Gosset approach, in honour of W.S. Gosset. In this paper, we compare the greeks for Gosset and Black-Scholes formulae and we discuss implementation. The t-distribution requires a shape parameter νto match the "fat tails" of the observed returns. For large ν, the Gosset and Black-Scholes formulae are equivalent. The Gosset formulae removes the requirement that the volatility be known, and in this sense can be viewed as an extension of the Black-Scholes formula.

q-fin.PR↗

arXiv2010

Quark nova inside supernova: Application to GRBs and XROs

In this paper we consider a quark nova occurring inside an exploding star. The quark nova ejecta will shock when interacting with the stellar envelope. When this shock reaches the surface of the star, the energy is radiated away. We suggest that this energy may be seen in X-rays, and show here that this may explain some flares seen in the X-ray afterglow of long gamma ray bursts (GRBs). A quark nova inside an exploding star need not be followed by a GRB, or the GRB may not be beamed towards us. However, the shock breakout is likely not beamed and could be seen even in the absence of a GRB. We suggest that XRO 080109 is such an event in which a quark nova occurs inside an exploding star. No GRB is formed, but the break out of the shock leads to the XRO.

astro-ph.HE↗

arXiv2010

Quark-nova remnants IV: Application to radio emitting AXP transients

(Abridged) XTE J1810-197 and 1E 1547.0-5408 are two transient AXPs exhibiting radio emission with unusual properties. In addition, their spin down rates during outburst show opposite trends, which so far has no explanation. Here, we extend our quark-nova model for AXPs to include transient AXPs, in which the outbursts are caused by transient accretion events from a Keplerian (iron-rich) degenerate ring. For a ring with inner and outer radii of 23.5 km and 26.5 km, respectively, our model gives a good fit to the observed X-ray outburst from XTE J1810-197 and the behavior of temperature, luminosity, and area of the two X-ray blackbodies with time. The two blackbodies in our model are related to a heat front (i.e. Bohm diffusion front) propagating along the ring's surface and an accretion hot spot on the quark star surface. Radio pulsations in our model are caused by dissipation at the light cylinder of magnetic bubbles, produced near the ring during the X-ray outburst. The delay between X-ray peak emission and radio emission in our model is related to the propagation time of these bubbles to the light cylinder. We predict a ~1 year and ~1 month delay for XTE J1810-197 and 1E 1547.0-5408, respectively. The observed flat spectrum, erratic pulse profile, and the pulse duration are all explained in our model as a result of X-point reconnection events induced by the dissipation of the bubbles at the light cylinder. The spin down rate of the central quark star can either increase or decrease depending on how the radial drift velocity of the magnetic islands changes with distance from the central star. We suggest an evolutionary connection between transient AXPs and typical AXPs in our model.

astro-ph↗

arXiv2010

The Meissner Effect and Vortex Expulsion in Color-Superconducting Quark stars, and its Role for Re-heating of Magnetars

Compact stars made of quark matter rather than confined hadronic matter, are expected to form a color superconductor. This superconductor ought to be threaded with rotational vortex lines, within which the star's interior magnetic field is at least partially confined. The vortices (and thus magnetic flux) would be expelled from the star during stellar spin-down, leading to magnetic reconnection at the surface of the star and the prolific production of thermal energy. In this paper, we show that this energy release can re-heat quark stars to exceptionally high temperatures, such as observed for Soft Gamma Repeaters (SGRs), Anomalous X-Ray pulsars (AXPs), and X-ray dim isolated neutron stars (XDINs). Moreover, our numerical investigations of the temperature evolution, spin-down rate, and magnetic field behavior of such superconducting quark stars suggest that SGRs, AXPs, and XDINs may be linked ancestrally. Finally, we discuss the possibility of a time delay before the star enters the color superconducting phase, which can be used to estimate the density at which quarks deconfine. From observations, we find this density to be of the order of five times that of nuclear saturation.

astro-ph.HE↗

arXiv2009

Predictions for signatures of the quark-nova in superluminous supernovae

[Abridged] Superluminous Supernovae (SN2006gy, SN2005gj, SN2005ap, SN2008fz, SN2003ma) have been a challenge to explain by standard models. We present an alternative scenario involving a quark-nova (QN), an explosive transition of the newly born neutron star to a quark star in which a second explosion (delayed) occurs inside the already expanding ejecta of a normal SN. The reheated SN ejecta can radiate at higher levels for longer periods of time primarily due to reduced adiabatic expansion losses, unlike the standard SN case. Our model is successfully applied to SN2006gy, SN2005gj, SN2005ap, SN2008fz, SN2003ma with encouraging fits to the lightcurves. There are four predictions in our model: (i) superluminous SNe optical lightcurves should show a double-hump with the SN hump at weaker magnitudes occurring days to weeks before the QN; (ii) Two shock breakouts should be observed vis-a-vis one for a normal SN. Depending on the time delay, this would manifest as two distinct spikes in the X-ray region or a broadening of the first spike for extremely short delays; (iii) The QN deposits heavy elements of mass number A> 130 at the base of the preceeding SN ejecta. These QN r-processed elements should be visible in the late spectrum (few days-weeks in case of strong ejecta mixing) of the superluminous SN; (iv) The QN yield will also contain lighter elements (Hydrogen and Helium). We expect the late spectra to include H_alpha emission lines that should be distinct in their velocity signature from standard H_alpha emission.

astro-ph.HE↗

arXiv2009

Pricing European Options with a Log Student's t-Distribution: a Gosset Formula

The distribution of the returns for a stock are not well described by a normal probability density function (pdf). Student's t-distributions, which have fat tails, are known to fit the distributions of the returns. We present pricing of European call or put options using a log Student's t-distribution, which we call a Gosset approach in honour of W.S. Gosset, the author behind the nom de plume Student. The approach that we present can be used to price European options using other distributions and yields the Black-Scholes formula for returns described by a normal pdf.

q-fin.PR↗

arXiv2009

Quark-nova explosion inside a collapsar: application to Gamma Ray Bursts

If a quark-nova occurs inside a collapsar, the interaction between the quark-nova ejecta (relativistic iron-rich chunks) and the collapsar envelope, leads to features indicative of those observed in Gamma Ray Bursts. The quark-nova ejecta collides with the stellar envelope creating an outward moving cap (Gamma ~ 1-10) above the polar funnel. Prompt gamma-ray burst emission from internal shocks in relativistic jets (following accretion onto the quark star) become visible after the cap becomes optically thin. Model features include: (i) precursor activity (optical, X-ray, gamma-ray), (ii) prompt gamma-ray emission, and (iii) afterglow emission. We discuss SN-less long duration GRBs, short hard GRBs (including association and non-association with star forming regions), dark GRBs, the energetic X-ray flares detected in Swift GRBs, and the near-simultaneous optical and gamma-ray prompt emission observed in GRBs in the context of our model.

astro-ph↗