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Register a new userEvaluating Systematic Dependencies of Type Ia Supernovae: The Influence of Deflagration to Detonation Density
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Aaron P. Jackson
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We explore the effects of the deflagration to detonation transition (DDT) density on the production of Ni-56 in thermonuclear supernova explosions (type Ia supernovae). Within the DDT paradigm, the transition density sets the amount of expansion during the deflagration phase of the explosion and therefore the amount of nuclear statistical equilibrium (NSE) material produced. We employ a theoretical framework for a well-controlled statistical study of two-dimensional simulations of thermonuclear supernovae with randomized initial conditions that can, with a particular choice of transition density, produce a similar average and range of Ni-56 masses to those inferred from observations. Within this framework, we utilize a more realistic simmered white dwarf progenitor model with a flame model and energetics scheme to calculate the amount of Ni-56 and NSE material synthesized for a suite of simulated explosions in which the transition density is varied in the range 1-3x10^7 g/cc. We find a quadratic dependence of the NSE yield on the log of the transition density, which is determined by the competition between plume rise and stellar expansion. By considering the effect of metallicity on the transition density, we find the NSE yield decreases by 0.055 +/- 0.004 solar masses for a 1 solar metallicity increase evaluated about solar metallicity. For the same change in metallicity, this result translates to a 0.067 +/- 0.004 solar mass decrease in the Ni-56 yield, slightly stronger than that due to the variation in electron fraction from the initial composition. Observations testing the dependence of the yield on metallicity remain somewhat ambiguous, but the dependence we find is comparable to that inferred from some studies.
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We present a study exploring a systematic effect on the brightness of type Ia supernovae using numerical models that assume the single-degenerate paradigm. Our investigation varied the central density of the progenitor white dwarf at flame ignition, and considered its impact on the explosion yield, particularly the production and distribution of radioactive Ni-56, which powers the light curve. We performed a suite of two-dimensional simulations with randomized initial conditions, allowing us to characterize the statistical trends that we present. The simulations indicate that production of Fe-group material is statistically independent of progenitor central density, but the mass of stable Fe-group isotopes is tightly correlated with central density, with a decrease in the production of Ni-56 at higher central densities. These results imply progenitors with higher central densities produce dimmer events. We provide details of the post-explosion distribution of Ni-56 in the models, including the lack of a consistent centrally-located deficit of Ni-56, which may be compared to observed remnants. By performing a self-consistent extrapolation of our model yields and considering the main-sequence lifetime of the progenitor star and the elapsed time between the formation of the white dwarf and the onset of accretion, we develop a brightness-age relation that improves our prediction of the expected trend for single degenerates and we compare this relation with observations.
Type Ia supernovae are bright stellar explosions thought to occur when a thermonuclear runaway consumes roughly a solar mass of degenerate stellar material. These events produce and disseminate iron-peak elements, and properties of their light curves allow for standardization and subsequent use as cosmological distance indicators. The explosion mechanism of these events remains, however, only partially understood. Many models posit the explosion beginning with a deflagration born near the center of a white dwarf that has gained mass from a stellar companion. In order to match observations, models of this single-degenerate scenario typically invoke a subsequent transition of the (subsonic) deflagration to a (supersonic) detonation that rapidly consumes the star. We present an investigation into the systematics of thermonuclear supernovae assuming this paradigm. We utilize a statistical framework for a controlled study of two-dimensional simulations of these events from randomized initial conditions. We investigate the effect of the composition and thermal history of the progenitor on the radioactive yield, and thus brightness, of an event. Our results offer an explanation for some observed trends of mean brightness with properties of the host galaxy.
We present a theoretical framework for formal study of systematic effects in Supernovae Type Ia (SN Ia) that utilizes 2-d simulations to implement a form of the deflagration-detonation transition (DDT) explosion scenario. The framework is developed from a randomized initial condition that leads to a sample of simulated SN Ia whose Ni56 masses have a similar average and range to those observed, and have many other modestly realistic features such as the velocity extent of intermediate mass elements. The intended purpose is to enable statistically well-defined studies of both physical and theoretical parameters of the SN Ia explosion simulation. We present here a thorough description of the outcome of the SN Ia explosions produced by our current simulations. A first application of this framework is utilized to study the dependence of the SN Ia on the Ne22 content, which is known to be directly influenced by the progenitor stellar populations metallicity. Our study is very specifically tailored to measure how the Ne22 content influences the competition between the rise of plumes of burned material and the expansion of the star before these plumes reach DDT conditions. This competition controls the amount of material in nuclear statistical equilibrium (NSE) and therefore Ni56 produced by setting the density at which nucleosynthesis takes place during the detonation phase of the explosion. Although the outcome following from any particular ignition condition can change dramatically with Ne22 content, with a sample of 20 ignition conditions we find that the systematic change in the expansion of the star prior to detonation is not large enough to compete with the dependence on initial neutron excess discussed by Timmes, Brown & Truran (2003). (Abridged)
It has long been recognized that the neutrinos detected from the next core-collapse supernova in the Galaxy have the potential to reveal important information about the dynamics of the explosion and the nucleosynthesis conditions as well as allowing us to probe the properties of the neutrino itself. The neutrinos emitted from thermonuclear - type Ia - supernovae also possess the same potential, although these supernovae are dimmer neutrino sources. For the first time, we calculate the time, energy, line of sight, and neutrino-flavor-dependent features of the neutrino signal expected from a three-dimensional delayed-detonation explosion simulation, where a deflagration-to-detonation transition triggers the complete disruption of a near-Chandrasekhar mass carbon-oxygen white dwarf. We also calculate the neutrino flavor evolution along eight lines of sight through the simulation as a function of time and energy using an exact three-flavor transformation code. We identify a characteristic spectral peak at $sim 10$ MeV as a signature of electron captures on copper. This peak is a potentially distinguishing feature of explosion models since it reflects the nucleosynthesis conditions early in the explosion. We simulate the event rates in the Super-K, Hyper-K, JUNO, and DUNE neutrino detectors with the SNOwGLoBES event rate calculation software and also compute the IceCube signal. Hyper-K will be able to detect neutrinos from our model out to a distance of $sim 10$ kpc. At 1 kpc, JUNO, Super-K, and DUNE would register a few events while IceCube and Hyper-K would register several tens of events.
Type Ia supernovae are bright stellar explosions distinguished by standardizable light curves that allow for their use as distance indicators for cosmological studies. Despite the highly successful use of these events in this capacity, many fundamental questions remain. Contemporary research investigates how properties of the progenitor system that follow from the host galaxy such as composition and age influence the brightness of an event with the goal of better understanding and assessing the intrinsic scatter in the brightness. We provide an overview of these supernovae and proposed progenitor systems, all of which involve one or more compact stars known as white dwarfs. We describe contemporary research investigating how the composition and structure of the progenitor white dwarf systematically influences the explosion outcome assuming the progenitor is a single white dwarf that has gained mass from a companion. We present results illustrating some of these systematic effects from our research.
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