No description available.

Dans la décennie précédente les supernovae se sont imposées comme une des sondes les plus puissantes pour reconstruire l'histoire globale de l'Univers. Cependant la standardisation des supernovae de type Ia est toujours une relation empirique. De futures expériences, tel que JDEM, sont prévues pour apporter une meilleure caractérisation de l'équation d'état de l'énergie noire responsable de l'accélération de l'Univers. Ces expériences nécessiterons un contrôle des erreurs systématiques pour assurer aux conclusions futures de n'être pas dominées par des effets non liés à la cosmologie. L'évolution des supernovae avec le redshift ou la présence de sous-classes parmi elles peuvent être à l'origine de ce type de systématiques. Ainsi une meilleure compréhension des propriétés des supernovae et de leur environnement pourrait apporter, une meilleure compréhension de leur standardisation, finalement une meilleure description des supernovae en tant qu'objets astrophysiques. Cette étude apporte également des informations traitant de la simulation de missions spatiales telles que JDEM / Over the past decade supernovae have emerged as one of the most powerful tools for reconstructing the global history of the Universe. However type Ia supernovae are still empirical tools. Future experiments, as JDEM, are planned to better characterize the equation of state of the dark energy leading to the observed acceleration thousands of objects. These experiments will need to carefully control systematic errors to ensure future conclusions are not dominated by effects unrelated to cosmology. The evolution of N Ia with redshift or the presence of subclasses among them can be at the origin of that kind os systematics. So a better understanding of the properties of supernovae in their host galaxies could provide information about the correlation between supernovae and their environment, a better understanding of their standardization, finally a better description of supernovae as astrophisical object. this study can also provide informations for more realistic simultations of a space mission like JDEM

We present a comprehensive study of interstellar X-ray extinction using the extensive Chandra supernova remnant (SNR) archive and use our results to refine the empirical relation between the hydrogen column density and optical extinction. In our analysis, we make use of the large, uniform data sample to assess various systematic uncertainties in the measurement of the interstellar X-ray absorption. Specifically, we address systematic uncertainties that originate from (i) the emission models used to fit SNR spectra; (ii) the spatial variations within individual remnants; (iii) the physical conditions of the remnant such as composition, temperature, and non-equilibrium regions; and (iv) the model used for the absorption of X-rays in the interstellar medium. Using a Bayesian framework to quantify these systematic uncertainties, and combining the resulting hydrogen column density measurements with the measurements of optical extinction toward the same remnants, we find the empirical relation N-H = (2.87 +/- 0.12) x 10(21) A(V) cm(-2), which is significantly higher than the previous measurements.

iPTF15dtg is a supernova (SN) Type Ic (lacking hydrogen and helium in its spectrum) with a light curve indicating that it is the result of a massive star explosion. Taddia et al. (2016) suggested that the progenitor star was a Wolf-Rayet (WR) star that previously suffered strong mass loss. More recent observations show that the SN light curve did not decline as expected, indicating the existence of an additional power source. One possibility is a magnetar, a hyper-magnetic neutron star capable of injecting its rotational energy into the light curve during relevant time scales. This bachelor thesis adds previously unpublished data to the iPTF15dtg light curve and compares simple semi-analytical models to rule out a radioactive scenario and discuss the possibility of a magnetar as the primary source of luminosity.

This thesis examines three core-collapse supernova remnants (SNR) - the Cygnus Loop in the Milky Way and 0453-68.5 and 0540-69.3 in the Large Magellanic Cloud - of varying ages and in varying states of interaction with the surrounding interstellar medium (ISM), using X-ray imaging spectroscopy with Chandra and supplemental data from other wavelengths. We use results from our analysis to address three main questions. First, we examine the applicability of the common Sedov-Taylor adiabatic blast wave model to core-collapse supernovae. Second, we determine the elemental abundances around the shell of these supernova remnants to determine if the use of SNRs as a gauge of abundances in the ISM is justified. Finally, we examine the pulsar wind nebulae (PWNe) in 0453-68.5 and 0540-69.3 and search for evidence of interaction between these PWNe and their immediate surroundings. We see highly inhomogeneous ISM surrounding all three surveyed SNRs, contrary to the key assumption in the Sedov-Taylor model of a uniform surrounding medium. In all three studied SNRs, we find that shock speeds are dependent on the density of the surrounding material. As subsidiary results, we also find depleted elemental abundances of oxygen, magnesium, and silicon, relative to typical ISM, around all three studied supernova remnants. Although this subsidiary result is not conclusive, we believe that it merits a followup study. In 0540-69.3 and 0453-68.5, which contain central pulsars, we find that the explosion directionality, which can be inferred from the pulsar's proper motion relative to the SNR, is not related to the morphology of the SNR itself. We conclude from this that the asymmetric shapes common in core-collapse supernova remnants can be more a function of the complex environments surrounding the progenitors of core- collapse supernovae than of the supernova explosions themselves. Finally, we see that the PWN in 0453-68.5 shows signs of having mixed with the surrounding thermal- emitting material, while the PWN in 0540-69.3 appears to have not mixed with or interacted with the surrounding SNR material to any substantial degree. We believe that this result may indicate that the degree of interaction between a PWN and its surroundings is dependent on age and possibly shell morphology, although further study is needed.

This thesis considers the various morphologies of radio supernova remnants (SNRs), and attempts to determine whether their appearance results from the properties of the progenitor star and its supernova explosion, or from the structure of the interstellar medium (ISM) and ambient magnetic field into which a SNR consequently expands. High-resolution observations of Supernova 1987A show a young remnant whose appearance and evolution are completely dominated by the structure of its progenitor wind. A statistical study of the Galactic population of bilateral SNRs demonstrates that the symmetry axes of these remnants run parallel to the Galactic Plane. This result can be explained by the interaction of main sequence stellar wind-bubbles with the ambient magnetic field; expansion of SNRs into the resulting elongated cavities results in a bilateral appearance with the observed alignment. Radio observations of SNR G296.8-00.3 show a double-ringed morphology which is best explained by expansion either into an anisotropic main-sequence progenitor wind or into multiple cavities in the ISM. Data on SNRs G309.2-00.6 and G320.4-01.2 (MSH 15-52) make a strong case that the appearance of both remnants is significantly affected by collimated outflows from a central source; for G309.2-00.6 the source itself is not detected, but for G320.4-01.2 there is now compelling evidence that the remnant is associated with and is interacting with the young pulsar PSR B1509-58. I conclude that, while the youngest SNRs are shaped by their progenitor's circumstellar material, the appearance of most SNRs reflects the properties of the local ISM and magnetic field. Remnants which interact with an associated pulsar or binary system appear to be rare, and are easily distinguished by their unusual and distorted morphologies.

Modern problems in astrophysics tend to require large, complex computational frameworks to solve many aspects of the system simultaneusly. Calculation of the energy production through nuclear reactions is typically one of those aspects. The use of standard nuclear burning algorithms will take up the majority of the computational time with all but the smallest of networks. The explicit asymptotic method has shown promise in computing large networks faster than existing methods in various environments while retaining accuracy. The purpose of this thesis is to show that this method can be successfully used to solve complex systems using a network of realistic size in a reasonable amount of time, and to investigate some problems in the flame propagation for a Type Ia, which have never been investigated with a realistic network.

In the standard model of cosmology, the universe is currently dominated by dark energy in the form of the cosmological constant that drives the expansion to accelerate. While the cosmological constant hypothesis is consistent with all current data, models with dynamical behaviour of dark energy are still allowed by observations. Uncertainty also remains over whether the underlying assumption of a homogeneous and isotropic universe is valid, or if large-scale inhomogeneities in the matter distribution can be the cause of the apparent late-time acceleration.This thesis investigates inhomogeneous cosmological models in which dark energy clusters or where we live inside an underdense region in a matter-dominated universe. In both of these scenarios, we expect directional dependences in the redshift-luminosity distance relation of type Ia supernovae. Dynamical models of dark energy predict spatial variations in the dark energy density. Searches for angular correlated fluctuations in the supernova peak magnitudes, as expected if dark energy clusters, yield results consistent with no dark energy fluctuations. However, the current observational limits on the amount of correlation still allow for quite general dark energy clustering occurring in the linear regime. Inhomogeneous models where we live inside a large, local void in the matter density can possibly explain the apparent acceleration without invoking dark energy. This scenario is confronted with current cosmological distance measurements to put constraints on the size and depth of the void, as well as on our position within it. The model is found to explain the observations only if the void size is of the order of the visible universe and the observer is located very close to the center, in violation of the Copernican principle. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Accepted.

Modern problems in astrophysics tend to require large, complex computational frameworks to solve many aspects of the system simultaneusly. Calculation of the energy production through nuclear reactions is typically one of those aspects. The use of standard nuclear burning algorithms will take up the majority of the computational time with all but the smallest of networks. The explicit asymptotic method has shown promise in computing large networks faster than existing methods in various environments while retaining accuracy. The purpose of this thesis is to show that this method can be successfully used to solve complex systems using a network of realistic size in a reasonable amount of time, and to investigate some problems in the flame propagation for a Type Ia, which have never been investigated with a realistic network.

A survey of the theory of neutrino oscillations in dense matter and neutrino backgrounds is presented. We discuss collective neutrino systems using the gyroscopic pendulum analogy and describe the motion that results from self-induced parametric resonances. The effects of dense matter on the flavour oscillations of neutrinos are also detailed. This theory is applied to the case of continuous supernova neutrino spectra and explanations of the spectral swapping behaviour seen in numerical studies are summarized. The results of numerical simulations of supernova oscillations in turbulent supernova backgrounds are presented and discussed. We study the motion of two example supernova neutrino spectra and examine the differences in the dynamics and flavour evolution that results from adding turbulent fluctuations to the supernova matter background. We also investigate the effect that fluctuations in the neutrino density can have on the oscillation behaviour. We find that in general the final neutrino spectra emerging from the inner supernova regions are quite robust to fluctuations in the backgrounds in our model, while the intermediate dynamics can be very strongly altered. Some significant changes in the final spectra are also found to occur when the neutrino background density fluctuations are large. We give a detailed review of the resonant matter effects that determine the survival probabilities of atmospheric muon neutrinos. The differences between various Earth density models are described, and these models are then used to predict the flux of muon-type neutrino events in the Deep Core extension to the IceCube detector. We use recent results from the detector collaboration and build on previous work which considered the sensitivity of the detector to the mass hierarchy, and show that uncertainties in the Earth's density can have a significant influence on the event rates.