Heidelberg, Universiẗat, Diss., 2000.

Made available in DSpace on 2014-06-11T19:25:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-07Bitstream added on 2014-06-13T18:07:22Z : No. of bitstreams: 1 arretche_f_me_ift.pdf: 686798 bytes, checksum: 3260fc9cb501cb26c825ba228e695e3a (MD5) / Neste trabalho, investigamos a viabilidade do mecanismo de pólo do píon ('gamagamaseta'pi''POT.0setaniuniu''BARRA') como mecanismo alternativo para o resfriamento do núcleo estelar de estrelas de alta massa durante o processo de colapso gravitacional. Em especial, concentramos nossa atenção no vínculo para a luminosidade de neutrinos emitidos pela supernova SN1987A. Mostramos que ao incorporar os efeitos do meio nuclear denso no propagador piônico através da eoria de Migdal para sistemas fermiônicos finitos, o mecanismo de pólo do píon é suprimido e que por causa diss não conseguimos obter nenhum vínculo significativo para o decaimento do píon em neutrinos. / Abstracts: In this work, we investigate the viability of the pion pole mechanism ('gamagamaseta'pi''POT.0setaniuniu''BARRA') as an alternative mechanism for the cooling of stellar nucleus of massive stars during the gravitational collapse. In particular we concentrate our attention on a possible constrain on the neutrino's luminosity from the supernova SN1987A. We show that incorporating the effects of the dense nuclear medium througt the Migdal's theory for finite fermionic systems in the pion propagator, the pion pole mechanism is supressed and we cannot obtain any meaningful constrain for the pion decay into neutrinos.

No description available.

The filamentary nebula RCW 86, identical with the non - thermal radio source MSH 14 - 63, is part of a supernova remnant. A group of OB stars is found near the radio source. The distance of the group is 2500 pc; this agrees well with the radio distance of the remnant. It is suggested that the remnant was formed by the explosion of a member of the group; the explosion occurred probably in 185 A. D.

In this work, high-energy observables arising during different phases of SN explosions are studied with respect to their potential for allowing conclusions on suggested explosion scenarios and physical mechanisms that are thought to influence the evolution of SNe in a major way. The focus on selected observables at keV and MeV energies is motivated by the appearance of large degeneracies that can even be found for disparate scenarios in many wavelength regimes. Since the discussed emission in the high-energy regime is directly linked to nuclear processes being usually very distinct for different suggested physical models, the signatures at keV and MeV energies allow for meaningful comparisons of simulations with observations. / In der vorliegenden Arbeit werden Hochenergie-Beobachtungsgrößen, die während verschiedener Phasen von Supernova-Explosionen entstehen, hinsichtlich der Möglichkeit von Rückschlüssen auf vorgeschlagene Explosionsszenarien und physikalische Mechanismen, welche einen wichtigen Einfluss auf die Entwicklung dieser Explosionen ausüben, untersucht. Die Schwerpunktsetzung auf Beobachtungsgrößen im keV- und MeV-Energiebereich ist dabei durch die großen Ähnlichkeiten begründet, die grundverschiedene Szenarien in ihrer Emission in vielen Wellenlängenbereichen zeigen. Da die diskutierten Beobachtungsgrößen im Hochenergie-Bereich direkt mit nuklearen Prozessen verknüpft sind, die bei unterschiedlichen physikalischen Modellen sehr charakteristisch ausgeprägt sein können, eignen sich gerade die vorgestellten Signaturen im keV- und MeV-Bereich für aussagekräftige Vergleiche von Simulationen und Beobachtungen.

Observations indicate that there is a correlation between long duration gamma-ray bursts (GRBs) and core-collapse supernovae (SNe). The leading model for GRB production assumes that relativistic jets are generated by the core-collapse within the progenitor star. Charged particles undergo Fermi-acceleration within internal shocks of these jets and subsequently give rise to gamma ray emission once the jets breach the surrounding stellar envelope. Very few SNe result in the occurrence of GRBs, however, it has been suggested that a significant fraction of core-collapse SNe manage to produce mildly relativistic jets. These jets are insufficiently energetic to break through the envelope and are effectively ’choked’ resulting in a lack of observed gamma ray emission. In both the failed and successful GRB scenario, neutrino production can occur if protons are accelerated in the internal shocks of these jets. These neutrinos may be detectable by the IceCube neutrino observatory and its low energy extension DeepCore. This thesis presents the methods and results of a dedicated search for temporal and spatial clustering of neutrino events during the IceCube 2012 data season. Examination of 22,040 neutrino event candidates acquired over a detector livetime of 330 days revealed no statistically significant transient source of neutrino emission. Limits on the rate of choked GRBs in the nearby universe for possible values of neutrino emission model parameters are presented.

This thesis is a theoretical study of the progenitors, event rates, and observational properties of unusually luminous supernova (SN), and aims to identify promising directions for future observations. In Chapter 2, we present model light curves and spectra of pair-instability supernovae (PISNe) over a range of progenitor masses and envelope structures for Pop III stars. We calculate the rates and detectability of PISNe, core-collapse supernovae (CCSNe), and Type Ia SNe at the Epoch of Reionization with the James Webb Space Telescope (JWST), which can be used to determine the contribution of Pop III versus Pop II stars toward ionizing the universe. Although CCSNe are the least intrinsically luminous supernovae, Chapter 5 shows that a JWST survey targeting known galaxy clusters with Einstein radii > 35'' should discover gravitationally lensed CCSNe at redshifts exceeding z = 7–8. In Chapter 3, we explain the Pop II/I progenitors of observed PISNe in the local universe can be created via mergers in runaway collisions in young, dense star clusters, despite copious mass loss via line-driven winds. The PISN rate from this mechanism is consistent with the observed volumetric rate, and the Large Synoptic Survey Telescope could discover \(\sim10^2\) such PISNe per year. In Chapter 4, we identify 10 star clusters which may host PISN progenitors with masses up to 600M⊙ formed via runaway collisions. We estimate the probabilities of these very massive stars being in eclipsing binaries to be \(\gtrsim 30%\), and find that their transits can be detected even under the contamination of the background cluster light, due to mean transit depths of\(\sim10^6L\)⊙. In Chapter 6, we show that there could be X-ray analogues of optically superluminous SNe that are powered by the conversion of the kinetic energy of SN ejecta into radiation upon its collision with a dense but optically-thin circumstellar shell. We find shell configurations that can convert a large fraction of the SN explosion energies into X-ray emission, producing unabsorbed X-ray luminosities of \(10^{44}\) erg/s in events lasting a few months, or even \(10^{45}\) erg/s flashes lasting days. / Physics

We present the results of three proposed mechanisms for ejection of gas from a spiral arm into the halo. The mechanisms were modelled using magnetohydrodynamics (MHD) as a theoretical template. Each mechanism was run through simulations using a Fortran code: ZEUS-3D, an MHD equation solver. The first mechanism modelled the gas dynamics with a modified Hartmann flow which describes the fluid flow between two parallel plates. We initialized the problem based on observation of lagging halos; that is, that the rotational velocity falls to a zero at some height above the plane of the disk. When adopting a density profile which takes into account the various warm and cold H$_I$ and H$_{II}$ molecular clouds, the system evolves very strangely and does not reproduce the steady velocity gradient observed in edge-on galaxies. This density profile, adopted from Martos and Cox (1998), was used in the remaining models. However, when treating a system with a uniform density profile, a stable simulation can result. Next we considered supernova (SN) blasts as a possible mechanism for gas ejection. While a single SN was shown to be insufficient to promote vertical gas structures from the disk, multiple SN explosions proved to be enough to promote gas ejection from the disk. In these simulations, gas ejected to a height of 0.5 kpc at a velocity of 130 km s$^{-1}$ from 500 supernovae, extending to an approximate maximum height of 1 kpc at a velocity of $6.7 \times 10^3$ km s$^{-1}$ from 1500 supernovae after 0.15 Myr, the approximate time of propagation of a supernova shock wave. Finally, we simulated gas flowing into the spiral arm at such a speed to promote a jump in the disk gas, termed a hydraulic jump. The height of the jump was found to be slightly less than a kiloparsec with a flow velocity of 41 km s$^{-1}$ into the halo after 167 Myr. The latter models proved to be effective mechanisms through which gas is ejected from the disk whereas the Hartmann flow (or toy model) mechanism remains unclear as the heliocentric velocity profile becomes unstable when run through a time-dependent simulation. Though the cause of this instability is unclear, pressure fluctuations in the system are suspected to play a role. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-01-05 17:52:59.532

Thesis (Ph. D.)--University of Sydney, 2001. / Includes tables. Title from title screen (viewed Apr. 22, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. Degree awarded 2001; thesis submitted 2000. Includes bibliography. Also available in print form.

Thesis (Ph. D.)--University of Sydney, 1999. / Title from title screen (viewed Apr. 16, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. Includes bibliography. Also available in print form.