京都大学 / 新制・課程博士 / 博士(理学) / 甲第24419号 / 理博第4918号 / 新制||理||1702(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 前田 啓一, 講師 LEE Shiu Hang, 教授 太田 耕司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Core-collapse supernovae are some of the most energetic events in the Universe, they herald the birth of neutron stars and black holes, are a major site for nucleosynthesis, influence galactic hydrodynamics, and trigger further star formation. As such, it is important to understand the mechanism of explosion. Moreover, observations imply that asymmetries are, in the least, a feature of the mechanism, and theory suggests that multi-dimensional hydrodynamics may be crucial for successful explosions. In this dissertation, we present theoretical investigations into the multi-dimensional nature of the supernova mechanism. It had been suggested that nuclear reactions might excite non-radial g-modes (the ε-mechanism) in the cores of progenitors, leading to asymmetric explosions. We calculate the eigenmodes for a large suite of progenitors including excitation by nuclear reactions and damping by neutrino and acoustic losses. Without exception, we find unstable g-modes for each progenitor. However, the timescales for growth are at least an order of magnitude longer than the time until collapse. Thus, the ε-mechanism does not provide appreciable amplification of non-radial modes before the core undergoes collapse. Regardless, neutrino-driven convection, the standing accretion shock instability, and other instabilities during the explosion provide ample asymmetry. To adequately simulate these, we have developed a new hydrodynamics code, BETHE-hydro that uses the Arbitrary Lagrangian-Eulerian (ALE) approach, includes rotational terms, solves Poisson’s equation for gravity on arbitrary grids, and conserves energy and momentum in its basic implementation. By using time dependent arbitrary grids that can adapt to the numerical challenges of the problem, this code offers unique flexibility in simulating astrophysical phenomena. Finally, we use BETHE-hydro to investigate the conditions and criteria for supernova explosions by the neutrino mechanism. We find that a critical luminosity/ mass-accretion-rate condition distinguishes non-exploding from exploding models in hydrodynamic 1D and 2D simulations. Importantly, the critical luminosity for 2D simulations is found to be ∼70% of the critical luminosity for 1D simulations. We identify the specifics ofmulti-dimensional hydrodynamic simulations that enable explosions at lower neutrino luminosities in 2D and discuss how these results might foreshadow successful explosions by eventual 3D radiation-hydrodynamic simulations.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22249号 / 理博第4563号 / 新制||理||1655(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 前田 啓一, 講師 LEE Shiu Hang, 教授 長田 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

I perform and analyse the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure effects. Based on the results of these calculations, I obtain the to-date most realistic estimates for the gravitational wave signal from collapse, bounce and the early postbounce phase of core collapse supernovae. I supplement my {3+1} GR hydrodynamic simulations with 2D Newtonian neutrino radiation-hydrodynamic supernova calculations focussing on (1) the late postbounce gravitational wave emission owing to convective overturn, anisotropic neutrino emission and protoneutron star pulsations, and (2) on the gravitational wave signature of accretion-induced collapse of white dwarfs to neutron stars. / Ich präsentiere die ersten Computer-Simulationen des rotierenden Kollapses stellarer Eisenkerne, die in der {3+1}-Zerlegung der Allgemeinen Relativitätstheorie durchgeführt werden und Vorsupernova-Sternmodelle aus Sternentwicklungsrechnungen, eine heiße nukleare Zustandsgleichung und ein näherungsweises Verfahren zur Beschreibung des Elektroneneinfangs enthalten und Neutrinodruck-Effekte berücksichtigen. Basierend auf den Ergebnissen dieser Rechnungen erhalte ich die zur Zeit realistischsten Vorhersagen für das Gravitationswellensignal der Kollaps, Abprall, Abkling und frühen Nach-Abprallphase einer Kern-Kollaps-Supernova. Neben den {3+1} Simulationen diskutiere ich newtonsche axisymmetrische Kern-Kollaps-Supernova-Simulationen mit Schwerpunkten auf: (1) der Gravitationswellenabstrahlung in der späten Nach-Abprallphase durch Konvektionsströmungen, anisotropische Neutrinoemission und Proto-Neutronenstern Pulsationen und (2) der Gravitationswellensignatur des Kollapses weißer Zwergsterne zu Neutronensternen, der durch Akkretion eingeleitet wird.

No description available.

<p>When modelling the collapse of massive stars leading to supernova explosions and the cooling of neutron stars, understanding the microphysical processes, such as the interaction of neutrinos within a dense medium are of vital importance. The interaction of neutrinos with nucleons (neutrons and protons) is altered by the presence of the medium, compared to the same process with free nucleons. Neutrino scattering and production processes may be characterized in terms of the excitations that are created or destroyed in the nuclear medium. One way to analyse the effects of the medium is by using Landau's theory of normal Fermi liquids. This theory gives simple relationships between physical quantities such as the spin susceptibility or the response to a weak interaction probe in terms of Landau parameters, that are measures of the interaction between quasiparticles. One problem when using Landau Fermi liquid theory for nucleon matter is that the interaction has a tensor component. The tensor interaction does not conserve the total spin and, as a consequence, there are generally contributions to long-wavelength response functions from states that have more than one quasiparticle-quasihole pair in the intermediate state. Such contributions cannot be calculated in terms of Landau parameters alone, since in the usual formulation of Landau theory, only singlepair excitations are considered. In this thesis three problems are addressed. First, we obtain bounds on the contributions from more than one quasiparticle-quasihole pair by using sum-rule arguments. Second, we derive expressions for static response functions allowing for the tensor components of the interaction. We analyse which the most important effects are on the static response of nucleon matter, and find that the major contributions comes from renormalization of coupling constants and transitions to states with more than one quasiparticle-quasihole pair. Third, we show how contributions to the dynamical response coming from states containing two quasiparticle-quasihole pairs may be evaluated in terms of Landau theory if one allows for the effect of collisions in the Landau kinetic equation. We consider the case of asymmetric nuclear matter, and our work goes beyond earlier works in that they contain the effects of collisions in addition to those of the mean field.</p>

When modelling the collapse of massive stars leading to supernova explosions and the cooling of neutron stars, understanding the microphysical processes, such as the interaction of neutrinos within a dense medium are of vital importance. The interaction of neutrinos with nucleons (neutrons and protons) is altered by the presence of the medium, compared to the same process with free nucleons. Neutrino scattering and production processes may be characterized in terms of the excitations that are created or destroyed in the nuclear medium. One way to analyse the effects of the medium is by using Landau's theory of normal Fermi liquids. This theory gives simple relationships between physical quantities such as the spin susceptibility or the response to a weak interaction probe in terms of Landau parameters, that are measures of the interaction between quasiparticles. One problem when using Landau Fermi liquid theory for nucleon matter is that the interaction has a tensor component. The tensor interaction does not conserve the total spin and, as a consequence, there are generally contributions to long-wavelength response functions from states that have more than one quasiparticle-quasihole pair in the intermediate state. Such contributions cannot be calculated in terms of Landau parameters alone, since in the usual formulation of Landau theory, only singlepair excitations are considered. In this thesis three problems are addressed. First, we obtain bounds on the contributions from more than one quasiparticle-quasihole pair by using sum-rule arguments. Second, we derive expressions for static response functions allowing for the tensor components of the interaction. We analyse which the most important effects are on the static response of nucleon matter, and find that the major contributions comes from renormalization of coupling constants and transitions to states with more than one quasiparticle-quasihole pair. Third, we show how contributions to the dynamical response coming from states containing two quasiparticle-quasihole pairs may be evaluated in terms of Landau theory if one allows for the effect of collisions in the Landau kinetic equation. We consider the case of asymmetric nuclear matter, and our work goes beyond earlier works in that they contain the effects of collisions in addition to those of the mean field.

Neutrino telescopes such as IceCube monitor for low-energy neutrinos O(10 MeV) produced in nuclear processes during core-collapse in supernovae. The detection horizon to the neutrino burst is 50 kpc, the distance to the Magellanic Clouds. However, this limits the number of supernovae accessible through low-energy neutrino detection, as the Galactic rate is only <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csim" data-classname="equation" data-title="" />2 per century. Some models predict the production of high-energy O(&gt;GeV) neutrinos through acceleration mechanisms, such as the ejecta colliding with the circumstellar material or relativistic jets in the stellar envelope. This thesis examines how these high-energy neutrinos could be exploited with neutrino telescopes like IceCube to extend the detection horizon to core-collapse supernovae past the Magellanic clouds. To examine the detection horizon for IceCube, we use two data samples, one utilizing muon tracks which provide good sensitivity in the northern sky, and the other all flavor starting events, which provide good sensitivity in the southern sky. We demonstrate that extending the reach past 50 kpc and well into the 10s of Mpc is possible, where the expected rate is more than two core-collapse supernovae per year.

The discovery of several bright supernovae (SNe) in recent years has evoked a great deal of interest in these objects. The study of these objects are of importance not only as probes to the end stages of stellar evolution, but also as probes for cosmology. Though the basic classification of supernovae was restricted to type I and type II, pecularities became apparent over the last two decades that have been confirmed into new classes, currently designated as types Ia, Ib, Ic, IIL, IIP, IIn and IIb. Diversity in the behaviour of supernovae within a class has also become apparent, such as photometric and spectroscopic sequence in type Ia, and the existence of the super-luminous‚ hypernovae‚ which, at times are found to be associated with GRB events. Core collapse supernovae are the end stages of most stars, more massive than ~ 8M . As such, they provide a key test of stellar evolution. Further, they play a major role in driving the chemical and dynamical evolution of galaxies, and have also been proposed to be major contributors to dust epochs when the Universe was still young. SNe explosions provide unique natural laboratories for studying, in real time, the physics of a variety of combustion, hydrodynamic, nuclear and atomic processes. All subclasses of SNe, except for type Ia, are core collapse events. The differences in the observed properties of the various subclasses, and even within a single subclass, may be attributed to the progenitor mass, metallicity and environment. The light curve and the spectral development would enable obtaining certain critical parameters related to the progenitor. It is hence important to study individual SNe events. The aim of this work is to (a) study the individual objects in detail and obtain critical parameters such as the radioactive Nickel mass ejected during the explosion, the mass of the ejected material, velocity with which the material has been ejected, the explosion energy and the distance to the supernova; (b) estimate progenitor mass and radius; (c) group the individual events according to certain common properties and inter-compare the properties of the various groups to arrive at a possible evolutionary sequence of the progenitors. This thesis consists of 6 chapters. Chapter 1 gives a general introduction to the evolution of massive stars and supernovae. Chapter 2 describes the telescope and instrument, observations and reduction procedures. All data were obtained using the 2m Himalayan Chandra Telescope (HCT), Hanle, India. The technical details of telescope and instrument are given in the chapter. This chapter also discusses in detail the various techniques used in photometric and spectroscopic data reductions. Chapter 3 discusses the properties of Type IIP supernovae with a detailed study of SN 2004A and SN 2008in. The distances to the supernovae are estimated using the Standard Candle Method (SCM) (Hamuy & Pinto, 2002) and the Expanding Photosphere Method (EPM)( Krishner & Kwan, 1974, 1975, Hamuy et al. 2001) . In addition, the explosion energy, radius of progenitor, the nickel mass and the mass ejected during the explosion are estimated using the observed light curves and the spectra (Hamuy 2003, Elmahamdi 2003, Litvinova & Nadyozhin 1985). The progenitor mass is also estimated based on the estimate of the ejected mass. Chapter 4 describes the evolution of the Type IIn supernova SN2005kd, which is characterized by narrow emission lines in the early spectra. Some Type IIn supernovae show a plateau phase in the light curve, and SN 2005kd is of this kind. The narrow emission lines in the spectra show that the SN ejecta interacted with the pre-supernova circumstellar material that is a result of mass loss from the progenitor during its evolution. Chapter 5 discusses the properties of stripped envelope core collapse supernovae using the observations of type Ib/c supernovae SN 2006jc, SN 2007ru, and SN 2009jf. SN 2006jc was found to be peculiar, with narrow He I emission lines arising due to the SN ejecta interaction with a helium enriched pre-supernova circumstellar material. SN 2007ru shows very broad lines in the spectra indicating a velocity of 20,000 kms−1 . The light curve evolution of SN 2007ru indicates a fast rise time and post-maximum decline more rapid than other broad-line Ic supernovae. The light curves of SN 2009jf are broad, with slow decline, indicating the presence of massive ejecta. He I line is identified with velocity of 16,000 km−1 . The photometric and spectroscopic evolution of all the above SNe are described in detail and compared with other similar supernovae. The various physical parameters related to the explosion and progenitors of SNe are also estimated. Chapter 6 is devoted to conclusions and future plans for the work in this thesis.

Les sources transitoires sont souvent associées aux phénomènes les plus violents de l’Univers, où l’accélération de hadrons peut avoir lieu. Parmi ces sources, les sursauts gamma, les noyaux actifs de galaxie ou encore les supernovae à effondrement de coeur sont des candidats prometteurs pour la production de rayons cosmiques et de neutrinos de haute énergie. Le télescope ANTARES, situé au fond de la Méditerranée, a pour but de détecter ces neutrinos, qui pourraient révéler la présence d’une source de rayons cosmiques. Cependant, pour augmenter la sensibilité aux sources transitoires, une méthode basée sur le suivi multi-longueur d’onde d’alertes neutrino a été développée au sein de la collaboration ANTARES. Ce programme, TAToO, permet de déclencher un réseau de télescopes optiques et l’instrument XRT du satellite Swift seulement quelques secondes après la détection d’un neutrino par ANTARES. Les télescopes commencent un programme d’observation de la région du ciel correspondante pour tenter de détecter une contrepartie optique ou X à l’évènement neutrino. Les travaux présentés dans cette thèse portent sur le développement et la mise en place d’un programme d’analyse d’images optiques, ainsi que sur l’analyse de données optiques et X obtenues lors des observations par les différents télescopes, pour identifier des sources transitoires rapides, telles que les émissions rémanentes de sursauts gamma, ou lentes, telles que les supernovae à effondrement de coeur. / Transient sources are often associated with the most violent phenomena in the Universe, where the acceleration of hadrons may occur. Such sources include gamma-ray bursts (GRBs), active galactic nuclei (AGN) or core-collapse supernovae (CCSNe), and are promising candidates for the production of high energy cosmic rays and neutrinos. The ANTARES telescope, located in the Mediterranean sea, aims at detecting these high energy neutrinos, which could reveal the presence of a cosmic ray accelerator. However, to enhance the sensitivity to transient sources, a method based on multi-wavelength follow-up of neutrino alerts has been developed within the ANTARES collaboration. This program, denoted as TAToO, triggers a network of robotic optical telescopes and the Swift-XRT with a delay of only few seconds after a neutrino detection. The telescopes start an observation program of the corresponding region of the sky in order to detect a possible electromagnetic counterpart to the neutrino event. The works presented in this thesis cover the development and implementation of an optical image analysis pipeline, as well as the analysis of optical and X-ray data to search for fast transient sources, such as GRB afterglows, and slowly varying transient sources, such as CCSNe.