This manuscript presents information for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) during 2015, its second full year of operations. The same information is presented for bright (m(V) <= 17), spectroscopically confirmed supernovae discovered by other sources in 2015. As with the first ASAS-SN bright supernova catalogue, we also present redshifts and near-ultraviolet through infrared magnitudes for all supernova host galaxies in both samples. Combined with our previous catalogue, this work comprises a complete catalogue of 455 supernovae from multiple professional and amateur sources, allowing for population studies that were previously impossible. This is the second of a series of yearly papers on bright supernovae and their hosts from the ASAS-SN team.

We consider the effect of free -streaming axion emission on numerical models for the cooling of the newly born neutron star associated with SN1987A. We find that for an axion mass of greater than -10-3 eV, axion emission shortens the duration of the expected neutrino burst so significantly that it would be inconsistent with the neutrino observations made by the Kamiokande II (KII) and Irvine -Michigan- Brookhaven (IMB) detectors. However, we have not investigated the possibility that axion trapping (which should occur for masses 20.02 eV) sufficiently reduces axion emission so that axion masses greater than -2 eV would be consistent with the neutrino observations.

We present multi-wavelength observations of SN 2014C during the first 500 days. These observations represent the first solid detection of a young extragalactic stripped-envelope SN out to high-energy X-rays similar to 40 keV. SN 2014C shows ordinary explosion parameters (E-k similar to 1.8 x 10(51) erg and M-ej similar to 1.7M circle dot). However, over an similar to 1 year timescale, SN 2014C evolved from an ordinary hydrogen-poor supernova into a strongly interacting, hydrogen-rich supernova, violating the traditional classification scheme of type-I versus type-II SNe. Signatures of the SN shock interaction with a dense medium are observed across the spectrum, from radio to hard X-rays, and revealed the presence of a massive shell of similar to 1Me of hydrogen-rich material at similar to 6. x. 10(16) cm. The shell was ejected by the progenitor star in the decades to centuries before collapse. This result challenges current theories of massive star evolution, as it requires a physical mechanism responsible for the ejection of the deepest hydrogen layer of H-poor SN progenitors synchronized with the onset of stellar collapse. Theoretical investigations point at binary interactions and/or instabilities during the last nuclear burning stages as potential triggers of the highly time-dependent mass loss. We constrain these scenarios utilizing the sample of 183 SNe Ib/c with public radio observations. Our analysis identifies SN 2014C-like signatures in similar to 10% of SNe. This fraction is reasonably consistent with the expectation from the theory of recent envelope ejection due to binary evolution if the ejected material can survive in the close environment for 10(3)-10(4) years. Alternatively, nuclear burning instabilities extending to core C-burning might play a critical role.

Lee Tak Wah = 第二類超新星爆發之電算模擬硏究 / 李德華. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaf 78). / Text in English; abstracts in English and Chinese. / Lee Tak Wah = Di er lei chao xin xing bao fa zhi dian suan mo ni yan jiu / Li Dehua. / Abstract --- p.i / Acknowledgments --- p.iii / Contents --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- A brief history of supernova --- p.1 / Chapter 1.2 --- Simulation of type II supernova --- p.3 / Chapter 2 --- Hydrodynamics --- p.6 / Chapter 2.1 --- Lagrangian hydrodynamics --- p.6 / Chapter 2.2 --- Finite difference representation --- p.7 / Chapter 2.3 --- Shock handling --- p.10 / Chapter 2.4 --- Stability and gravitation --- p.11 / Chapter 2.5 --- Test of the hydrodynamic code --- p.12 / Chapter 3 --- Equation of state --- p.17 / Chapter 3.1 --- Electrons and photons --- p.17 / Chapter 3.2 --- Nuclear equation of state --- p.20 / Chapter 3.2.1 --- Bulk energy --- p.21 / Chapter 3.2.2 --- Surface and Coulomb energy --- p.22 / Chapter 3.2.3 --- Nuclei to bubbles phase --- p.23 / Chapter 3.2.4 --- Translational energy --- p.24 / Chapter 3.2.5 --- Nucleons outside nuclei and α particles --- p.24 / Chapter 3.2.6 --- Nuclear statistical equilibrium --- p.25 / Chapter 3.3 --- Results along the isentropes --- p.26 / Chapter 4 --- Electrons and neutrinos behaviour --- p.40 / Chapter 4.1 --- Electron capture --- p.40 / Chapter 4.1.1 --- Electron capture on heavy nuclei --- p.41 / Chapter 4.1.2 --- Electron capture on free protons --- p.42 / Chapter 4.2 --- Neutrino leakage scheme --- p.43 / Chapter 5 --- Core collapse simulation --- p.45 / Chapter 5.1 --- Initial models --- p.45 / Chapter 5.2 --- General features of core collapse --- p.52 / Chapter 5.3 --- After the core bounce --- p.63 / Chapter 6 --- Discussion --- p.72 / Chapter 6.1 --- Conclusion --- p.72 / Chapter 6.2 --- Further development --- p.73 / Chapter A --- Artificial viscosity --- p.75 / Bibliography --- p.78

Reproduction de : Thèse de doctorat : Physique des particules : Lyon 1 : 2005. Reproduction de : Thèse de doctorat : Physique des Particules : Université d'Oklahoma : 2005. / Thèse soutenue en co-tutelle. Titre provenant de l'écran titre. 22 réf. bibliogr.

Supercomputer technology has revolutionized our studies of the most energetic astrophysical phenomena. Here, I present my simulations of energetic outbursts of gamma rays and the explosions of massive stars, and my efforts to further the computational astrophysics frontier with the development of a radiation hydrodynamics code. First, I present axisymmetric hydrodynamical simulations of the long-term accretion of a rotating gamma-ray burst (GRB) progenitor star, a "collapsar," onto the central compact object, which we assume is a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in two spatial dimensions and with an explicit shear viscosity. The evolution of the central accretion rate exhibits phases reminiscent of the long GRB [gamma]-ray and X-ray light curve, which lends support to the proposal by Kumar et al. (2008a,b) that the luminosity is modulated by the central accretion rate. In the first "prompt" phase, the black hole acquires most of its final mass through supersonic quasiradial accretion occurring at a steady rate of ~ 0.2 [solar mass] s⁻¹. After a few tens of seconds, an accretion shock sweeps outward through the star. The formation and outward expansion of the accretion shock is accompanied by a sudden and rapid power-law decline in the central accretion rate [mathematical formula], which resembles the L [subscript x] [is proportional to] t⁻³ decline observed in the X-ray light curves. The collapsed, shock-heated stellar envelope settles into a thick, low-mass equatorial disk embedded within a massive, pressure-supported atmosphere. After a few hundred seconds, the inflow of low-angular-momentum material in the axial funnel reverses into an outflow from the thick disk. Meanwhile, the rapid decline of the accretion rate slows, which is potentially suggestive of the "plateau"' phase in the X-ray light curve. We complement our adiabatic simulations with an analytical model that takes into account the cooling by neutrino emission and estimate that the duration of the prompt phase will be ~ 20 s. The model suggests that the steep decline in GRB X-ray light curves is triggered by the circularization of the infalling stellar envelope at radii where the virial temperature is below 10¹⁰ K, such that neutrino cooling is inefficient and an outward expansion of the accretion shock becomes imminent; GRBs with longer prompt [gamma]-ray emission should have more slowly rotating envelopes. Observational evidence suggests a link between long GRBs and Type Ic supernovae. I propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. I present spherically-symmetric hydrodynamic simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in one spatial dimension and with rotation, explicit shear viscosity, and convection in the mixing length theory approximation. Once the accretion flow becomes rotationally supported outside of the black hole, an accretion shock forms and traverses the stellar envelope. Energy is carried from the central geometrically thick accretion disk to the stellar envelope by convection. Energy losses through neutrino emission and nuclear photodisintegration are calculated but do not seem important following the rapid early drop of the accretion rate following circularization. We find that the shock velocity, energy, and unbound mass are sensitive to convective efficiency, effective viscosity, and initial stellar angular momentum. Our simulations show that given the appropriate combinations of stellar and physical parameters, explosions with energies ~ 5 x 10⁵⁰ ergs, velocities ~ 3000 km s⁻¹, and unbound material masses > 5 [solar mass] are possible in a rapidly rotating 16 [solar mass] main sequence progenitor star. Further work is needed to constrain the values of these parameters, to identify the likely outcomes in more plausible and massive LRGB progenitors, and to explore nucleosynthetic implications. In many high-energy astrophysical phenomena, the force of radiation pressure will have a direct effect on the hydrodynamics. Observing radiation is also the primary way we investigate our universe. With this in mind, I present my expansion of the FLASH hydrodynamics code, where I have implemented a gray, flux-limited diffusion (FLD) radiation hydrodynamics (RHD) solver. My solver utilizes the FLASH's diffusion packages that are powered by HYPRE. I have written a new, efficient radiation-matter coupling solver, which exactly integrates the equations for radiation-matter coupling and operates without any time step restrictions. I have also rewritten the unsplit hydrodynamics solver in FLASH to incorporate the changes in PPM characteristic tracing and the Riemann solver required to properly capture the radiation pressure force in regions that are not entirely optically thick. This has required the addition of a new Riemann solver to FLASH, similar to the Riemann solver in the CASTRO RHD code. I then present my validation tests of the code. This code will be made publicly available. / text

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

The explosion of massive stars involves the formation of a shock wave. In stars that develop iron cores, this shock wave stalls on its way out due to neutrino emission and the breakup of heavy nuclei flowing through the shock. For the explosion to succeed, a fraction of the gravitational binding energy of the collapsed core that is radiated in neutrinos needs to be absorbed by the material below the shock. How much energy is needed depends on the interplay between non-spherical hydrodynamic instabilities, neutrino heating, and nuclear dissociation. This thesis seeks to understand this interplay through numerical experiments that model the key physical components of the system and separate them out to examine their individual effects. Specifically, one- and two-dimensional time-dependent hydrodynamic simulations are performed to study the effects of non-spherical shock oscillations, neutrino-driven convection, and alpha particle recombination on the dynamics of the system and the critical heating rate for explosion. We find that nuclear dissociation has a significant effect on the linear stability and saturation amplitude of shock oscillations. At the critical neutrino heating rate for an explosion, convection due to a negative entropy gradient plays a major role in driving dipolar shock motions. One dimensional explosions are due to a global instability involving the advection of entropy perturbations from the shock to the region where the accretion flow cools due to neutrino emission. Large scale shock expansions in two-dimensions are due to a finite amplitude instability involving the balance between buoyancy forces and the ram pressure of the flow upstream of the shock. During these expansions, a significant amount of energy is released when nucleons recombine into alpha particles, constituting a significant last step in the transition to explosion. The critical neutrino heating rate for an explosion depends sensitively on the starting radius of the shock relative to the radius at which the binding energy of an alpha particle is comparable to the gravitational binding energy.

Proefschrift Universiteit van Amsterdam. / Met lit. opg. - Met samenvatting in het Nederlands.

Thesis (M. Sc.)--University of Sydney, 2001. / Title from title screen (viewed Apr. 23, 2008). Submitted in fulfilment of the requirements for the degree of Master of Science to the School of Physics, Faculty of Science. Includes bibliography. Also available in print form.