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

The standard model of particle physics cannot currently explain the origin of neutrino masses and anomalies that have been observed at different experiments. One solution for this is to introduce a beyond the standard model origin for these issues, which introduces a coupling between neutrinos and dark matter. Such an interaction would have implications on cosmology and would be constrained by astrophysical neutrino sources. A promising astrophysical source to probe this interaction is core-collapse supernovae as they release ~3x10^53 erg in neutrinos for each transient. However, more observations that constrain the internal physics of core-collapse supernovae are needed in order to better understand their neutrino emission. This dissertation studies two probes of internal physics that allow for a better understanding of the neutrino emission from core-collapse supernovae. The first is a novel approach to try and detect more supernova neutrinos that do not come from galactic events nor from the diffuse supernova background. This is accomplished by doing an offline timing coincidence search at neutrino detectors with a search window determined by optical observations of core-collapse supernovae. With a two-tank Hyper-Kamiokande, this allows for ~1 neutrino detection every 10 years with a confidence level of ~2.6 sigma, resulting from low nearby core-collapse rates and large background rates in the energy range of interest. The second probe of internal physics is high energy gamma-rays from the decays of unstable nuclei in proto-magnetar jets. The abundance distribution of the unstable nuclei depends directly on the neutrino emission, which controls the electron fraction, as well as properties of the proto-magnetar. We find that different proto-magnetar properties produce gamma-ray signals that are distinguishable from each other, and multiple types of observations allow for estimations of the jet and proto-magnetar properties. These gamma-ray signals are detectable for on-axis jets out to extragalactic distances, ~35 Mpc in the best case, and for off-axis jets the signal is only detectable for galactic or local galaxies depending upon the viewing angle. This dissertation also studies a phenomenological constraint on the interactions between neutrinos and dark matter. Using the neutrino emission from supernovae and the inferred dark matter distributions in Milky Way dwarf spheroidals, we constrain the amount of energy the neutrinos can inject into the dark matter sub-halos. This then allows a constraint on the interaction cross-section between neutrinos and dark matter with assumptions about the interaction kinematics. Assuming Lambda-CDM to be correct, the neutrinos cannot interact with low mass dark matter too often as it will become gravitationally unbound, changing the mass of the core we see today. For high mass dark matter, neutrinos can only inject a fraction of ~6.8x10^-6 of their energy in order to not conflict with estimates of the current shapes of the dark matter sub-halos. The constraints we obtain are sigma_nu-DM(E_nu=15 MeV, m_DM>130 GeV) ~ 3.4x10^-23 cm^2 and sigma_nu-DM(E_nu=15 MeV, m_DM <130 GeV) ~ 3.2x10^-27} (m_DM/1 GeV)^2 cm^2, which is slightly stronger than previous bounds for these energies. Consideration of baryonic feedback or host galaxy effects on the dark matter profile can strengthen this constraint. / Doctor of Philosophy / In our current understanding of the physics of the particles that govern how the universe behaves, there is no way to explain the properties we observe for the neutrino. Neutrinos were originally theorized to have zero mass, however neutrino experiments suggests otherwise. The current model of particle physics cannot explain how the neutrinos have mass, therefore an viable way to explain it is to introduce new physics that can generate the neutrino masses. A way to do this is to allow the neutrinos to interact with dark matter, which is matter that does not interact with light and is therefore invisible to the human eye. We know dark matter should exist in the universe due to the gravitational effects it has, making things like galaxies much heavier than what the stars and gas we see can explain. If neutrinos and dark matter interact, we should be able to see the effects of these interactions in the universe, and also possibly at locations where many neutrinos are produced. One such source of neutrinos in the universe are core-collapse supernovae, which are the deaths of massive stars and produce copious amounts of neutrinos. This dissertation studies signals that allow us to better understand the neutrino emission from core-collapse supernovae. One of these signals comes from summing the neutrinos we detect from many distant core-collapse supernovae. This technique uses the optical observations of the supernovae to give us a time window around which we can go through neutrino detector data to find if there are any neutrino detections that cannot be explained as coming from background events. Another method is to observe gamma-rays, high energy photons, that come from the radioactive decay of elements in jets moving near the speed of light powered by rare core-collapse supernovae. The specific gamma-rays and the overall brightness of them allows for an estimation of the properties of the neutrino emission and properties of the central engine that accelerates the jet to near the speed of light. This dissertation also studies the implications of a possible interactions in small and dim satellite galaxies of the Milky Way known as dwarf spheroidals. The shape of the dark matter that is distributed in these dwarf spheroidals can be inferred from the motion of the stars in that dwarf spheroidal, and this shape disagrees with the prevailing theory of dark matter in the universe. We take advantage of this disagreement to place an upper limit on both the mass loss that can occur in this region and the energy that past core-collapse supernovae within the dwarf spheroidals can inject into the dark matter. The mass loss bound lets us place a constraint on how often neutrinos can interact with light dark matter particles. The energy injection limit and an assumption on the energy transfer in each interaction between dark matter and neutrinos allows us to constrain how often the interaction can occur for heavy dark matter particles.

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.