Single point off-center helium ignitions as origin of some Type Ia supernovae (original) (raw)
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Sub-Chandrasekhar mass models for Type IA supernovae
The Astrophysical Journal, 1994
For carbon-oxygen white dwarfs accreting hydrogen or helium at rates in the range ∼ 1-10 ×10 −8 M ⊙ y −1 , a variety of explosive outcomes is possible well before the star reaches the Chandrasekhar mass. These outcomes are surveyed for a range of white dwarf masses (0.7-1.1 M ⊙), accretion rates (1 − 7 × 10 −8 M ⊙ y −1), and initial white dwarf temperatures (0.01 and 1 L ⊙). The results are particularly sensitive to the convection that goes on during the last few minutes before the explosion. Unless this convection maintains a shallow temperature gradient, and unless the density is sufficiently high, the accreted helium does not detonate. Below a critical helium ignition density, which we estimate to be 5 − 10 × 10 5 g cm −3 , either helium novae or helium deflagrations result. The hydrodynamics, nucleosynthesis, light curves, and spectra of a representative sample of detonating and deflagrating models are explored. Some can be quite faint indeed, powered at peak for a few days by the decay of 48 Cr and 48 V. Only the hottest, most massive white dwarfs considered with the smallest helium layers, show reasonable agreement with the light curves and spectra of common Type Ia supernovae. For the other models, especially those involving lighter white dwarfs, the helium shell mass exceeds 0.05 M ⊙ and the mass of the 56 Ni that is synthesized exceeds 0.01 M ⊙. These explosions do not look like ordinary Type Ia supernovae, or any other frequently observed transient.
Sub-Chandrasekhar Mass Models for Supernovae
The Astrophysical Journal, 2011
For carbon-oxygen white dwarfs accreting hydrogen or helium at rates in the range ∼ 1-10 ×10 −8 M ⊙ y −1 , a variety of explosive outcomes is possible well before the star reaches the Chandrasekhar mass. These outcomes are surveyed for a range of white dwarf masses (0.7-1.1 M ⊙), accretion rates (1 − 7 × 10 −8 M ⊙ y −1), and initial white dwarf temperatures (0.01 and 1 L ⊙). The results are particularly sensitive to the convection that goes on during the last few minutes before the explosion. Unless this convection maintains a shallow temperature gradient, and unless the density is sufficiently high, the accreted helium does not detonate. Below a critical helium ignition density, which we estimate to be 5 − 10 × 10 5 g cm −3 , either helium novae or helium deflagrations result. The hydrodynamics, nucleosynthesis, light curves, and spectra of a representative sample of detonating and deflagrating models are explored. Some can be quite faint indeed, powered at peak for a few days by the decay of 48 Cr and 48 V. Only the hottest, most massive white dwarfs considered with the smallest helium layers, show reasonable agreement with the light curves and spectra of common Type Ia supernovae. For the other models, especially those involving lighter white dwarfs, the helium shell mass exceeds 0.05 M ⊙ and the mass of the 56 Ni that is synthesized exceeds 0.01 M ⊙. These explosions do not look like ordinary Type Ia supernovae, or any other frequently observed transient.
Pulsating reverse detonation models of Type Ia supernovae. II: Explosion
Observational evidences point to a common explosion mechanism of Type Ia supernovae based on a delayed detonation of a white dwarf. However, all attempts to find a convincing ignition mechanism based on a delayed detonation in a destabilized, expanding, white dwarf have been elusive so far. One of the possibilities that has been invoked is that an inefficient deflagration leads to pulsation of a Chandrasekhar-mass white dwarf, followed by formation of an accretion shock that confines a carbon-oxygen rich core, while transforming the kinetic energy of the collapsing halo into thermal energy of the core, until an inward moving detonation is formed. This chain of events has been termed Pulsating Reverse Detonation (PRD). In this work we present three dimensional numerical simulations of PRD models from the time of detonation initiation up to homologous expansion. Different models characterized by the amount of mass burned during the deflagration phase, M_defl, give explosions spanning a range of kinetic energies, K ~ (1.0-1.2) foes, and 56Ni masses, M(56Ni) ~ 0.6-0.8 M_sun, which are compatible with what is expected for typical Type Ia supernovae. Spectra and light curves of angle-averaged spherically symmetric versions of the PRD models are discussed. Type Ia supernova spectra pose the most stringent requirements on PRD models.
PULSATING REVERSE DETONATION MODELS OF TYPE Ia SUPERNOVAE. I. DETONATION IGNITION
The Astrophysical Journal, 2009
Observational evidences point to a common explosion mechanism of Type Ia supernovae based on a delayed detonation of a white dwarf. However, all attempts to find a convincing ignition mechanism based on a delayed detonation in a destabilized, expanding, white dwarf have been elusive so far. One of the possibilities that has been invoked is that an inefficient deflagration leads to pulsation of a Chandrasekhar-mass white dwarf, followed by formation of an accretion shock that confines a carbon-oxygen rich core, while transforming the kinetic energy of the collapsing halo into thermal energy of the core, until an inward moving detonation is formed. This chain of events has been termed Pulsating Reverse Detonation (PRD). In this work we present three dimensional numerical simulations of PRD models from the time of detonation initiation up to homologous expansion. Different models characterized by the amount of mass burned during the deflagration phase, M defl , give explosions spanning a range of kinetic energies, K ∼ (1.0 − 1.2) × 10 51 erg, and 56 Ni masses, M ( 56 Ni) ∼ 0.6 − 0.8 M ⊙ , which are compatible with what is expected for typical Type Ia supernovae. Spectra and light curves of angle-averaged spherically symmetric versions of the PRD models are discussed. Type Ia supernova spectra pose the most stringent requirements on PRD models.
Type Ia Supernova Explosion: Gravitationally Confined Detonation
The Astrophysical Journal, 2004
We present a new mechanism for Type Ia supernova explosions in massive white dwarfs. The proposed scenario follows from relaxing the assumption of symmetry in the model and involves a detonation created in an unconfined environment. The explosion begins with an essentially central ignition of stellar material initiating a deflagration. This deflagration results in the formation of a buoyantly-driven bubble of hot material that reaches the stellar surface at supersonic speeds. The bubble breakout forms a strong pressure wave that laterally accelerates fuel-rich outer stellar layers. This material, confined by gravity to the white dwarf, races along the stellar surface and is focused at the location opposite to the point of the bubble breakout. These streams of nuclear fuel carry enough mass and energy to trigger a detonation just above the stellar surface. The flow conditions at that moment support a detonation that will incinerate the white dwarf and result in an energetic explosion. The stellar expansion following the deflagration redistributes stellar mass in a way that ensures production of intermediate mass and iron group elements consistent with observations. The ejecta will have a strongly layered structure with a mild amount of asymmetry following from the early deflagration phase. This asymmetry, combined with the amount of stellar expansion determined by details of the evolution (principally the energetics of deflagration, timing of detonation, and structure of the progenitor), can be expected to create a family of mildly diverse Type Ia supernova explosions.
TYPE Ia SUPERNOVAE FROM MERGING WHITE DWARFS. II. POST-MERGER DETONATIONS
The Astrophysical Journal, 2014
Merging carbon-oxygen (CO) white dwarfs are a promising progenitor system for Type Ia supernovae (SN Ia), but the underlying physics and timing of the detonation are still debated. If an explosion occurs after the secondary star is fully disrupted, the exploding primary will expand into a dense CO medium that may still have a disk-like structure. This interaction will decelerate and distort the ejecta. Here we carry out multi-dimensional simulations of "tamped" SN Ia models, using both particle and grid-based codes to study the merger and explosion dynamics, and a radiative transfer code to calculate synthetic spectra and light curves. We find that post-merger explosions exhibit an hourglass-shaped asymmetry, leading to strong variations in the light curves with viewing angle. The two most important factors affecting the outcome are the scale-height of the disk, which depends sensitively on the binary mass ratio, and the total 56 Ni yield, which is governed by the central density of the remnant core. The synthetic broadband light curves rise and decline very slowly, and the spectra generally look peculiar, with weak features from intermediate mass elements but relatively strong carbon absorption. We also consider the effects of the viscous evolution of the remnant, and show that a longer time delay between merger and explosion probably leads to larger 56 Ni yields and more symmetrical remnants. We discuss the relevance of this class of aspherical "tamped" SN Ia for explaining the class of "super-Chandrasekhar" SN Ia.
We argue that type Ia supernovae (SNe Ia) are the result of head-on collisions of White Dwarfs (WDs) in triple systems. The thermonuclear explosions resulting from the zero-impact-parameter collisions of WDs are calculated from first principles by using 2D hydrodynamical simulations. Collisions of typical WDs with masses 0.5-0.9 M_Sun result in explosions that synthesize Ni56 masses in the range of 0.15-0.8 M_Sun, spanning the wide distribution of yields observed for the majority of SNe Ia. The robustness of the shock ignition process is verified with a detailed study using a one-dimensional toy model and analytic tools. The late-time (~50 days after peak) bolometric light curve is equal to the instantaneous energy deposition and is calculated exactly, by solving the transport of gamma-rays emitted by the decay of Ni56 using a Monte-Carlo code. All collisions are found to have the same late-time light curves, when normalized to the amount of synthesized Ni56. This universal light cu...
The response of a helium white dwarf to an exploding Type Ia supernova
Monthly Notices of the Royal Astronomical Society, 2015
We conduct numerical simulations of the interacting ejecta from an exploding CO white dwarf (WD) with the He WD donor in the double-detonation scenario for Type Ia supernovae (SNe Ia), and find that the descendant supernova remnant (SNR) is highly asymmetrical, in contradiction with observations. When the donor He WD has low mass, M WD = 0.2M ⊙ , it is at a distance of ∼ 0.08R ⊙ from the explosion, and helium is not ignited. The low mass He WD casts an 'ejecta shadow' behind it, that has imprint in the SN remnant (SNR) hundreds of years later. The outer parts of the shadowed side are fainter and its boundary with the ambient gas is somewhat flat. These features are not found in known SNRs. More massive He WD donors, M WD ≃ 0.4M ⊙ , must be closer to the CO WD to transfer mass. At a distance a 0.045R ⊙ helium is ignited and the He WD explodes. This explosion leads to a highly asymmetrical SNR and to ejection of ∼ 0.15M ⊙ of helium, both of which contradict observations of SNe Ia.
Chandrasekhar Mass Models for Type Ia Supernovae
Annals of the New York Academy of Sciences, 1995
Given the difficulty arriving at a critical mass carbon-oxygen core, possible nucleosynthetic restrictions, and the existence of competing sub-Chandrasekhar mass models (see introduction, ref. l), one may wonder if there are compelling reasons to think that any Type Ia supernovae must result from the explosion of what has been our "standard model" -a 1.39 M, white dwarf made mostly of carbon and oxygen. Ultimately the case must be made with spectra and light curves, but for now we begin by noting at least one compelling reason, namely the existence of unique nucleosynthesisthe abundances of 48Ca, 50Ti, 54Cr, "Fe, and possibly 66Zn that exist in the sun. For their production, these nuclei require material that has gone to nuclear statistical equilibrium (NSE) with a large neutron excess, Ye = 0.42 and, moreover, that material must have low entropy so as to avoid an a-rich freeze out. Though neutron-rich zones may be found in Type I1 supernovae near the neutron star, they are always characterized by high entropy. Consequently 48Ca and similar nuclei are never produced in appreciable quantitieri in massive stars (though "Fe and 66Zn can be made by the s-process).
On the Progenitors of Type IA Supernovae
Cosmic Chemical Evolution, 2002
Models for Type Ia Supernovae (SNe Ia) are reviewed. It is shown that there are strong reasons to believe that SNe Ia represent thermonuclear disruptions of C-O white dwarfs, when these white dwarfs reach the Chandrasekhar limit and ignite carbon at their centers.