Galaxies, and clusters of galaxies, can act as gravitational lenses and magnify the light of objects behind them. The effect enables observations of very distant supernovae, that otherwise would be too faint to be detected by existing telescopes, and allows studies of the frequency and properties of these rare phenomena when the universe was young. Under the right circumstances, multiple images of the lensed supernovae can be observed, and due to the variable nature of the objects, the difference between the arrival times of the images can be measured. Since the images have taken different paths through space before reaching us, the time-differences are sensitive to the expansion rate of the universe. One class of supernovae, Type Ia, are of particular interest to detect. Their well known brightness can be used to determine the magnification, which can be used to understand the lensing systems. In this thesis, galaxy clusters are used as gravitational telescopes to search for lensed supernovae at high redshift. Ground-based, near-infrared and optical search campaigns are described of the massive clusters Abell 1689 and 370, which are among the most powerful gravitational telescopes known. The search resulted in the discovery of five photometrically classified, core-collapse supernovae at redshifts of 0.671&lt;z&lt;1.703 with significant magnification from the cluster. Owing to the power of the lensing cluster, the volumetric core-collapse supernova rates for 0.4 ≤ z &lt; 2.9 were calculated, and found to be in good agreement with previous estimates and predictions from cosmic star formation history. During the survey, two Type Ia supernovae in A1689 cluster members were also discovered, which allowed the Type Ia explosion rate in galaxy clusters to be estimated. Furthermore, the expectations of finding lensed supernovae at high redshift in simulated search campaigns that can be conducted with upcoming ground- and space-based telescopes, are discussed. Magnification from a galaxy lens also allows for detailed studies of the supernova properties at high redshift that otherwise would not be possible. Spectroscopic observations of lensed high-redshift supernovae Type Ia are of special interest since they can be used to test for evolution of the standard candle nature of these objects. If systematic redshift-dependent properties are found, their utility for future surveys could be challenged. In the thesis it is shown that the strongly lensed and very distant supernova Type Ia PS1-10afx at z=1.4, does not deviate from the well-studied nearby and intermediate populations of normal supernovae Type Ia. In a different study, the discovery of the first resolved multiply-imaged gravitationally lensed supernova Type Ia is also reported. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

We explore the effects of rotation on convective carbon, oxygen, and silicon shell burning during the late stages of evolution in a 20 M-circle dot star. Using the Modules for Experiments in Stellar Astrophysics we construct one-dimensional (1D) stellar models both with no rotation and with an initial rigid rotation of 50% of critical. At different points during the evolution, we map the 1D models into 2D and follow the multidimensional evolution using the FLASH compressible hydrodynamics code for many convective turnover times until a quasi-steady state is reached. We characterize the strength and scale of convective motions via decomposition of the momentum density into vector spherical harmonics. We find that rotation influences the total power in solenoidal modes, with a slightly larger impact for carbon and oxygen shell burning than for silicon shell burning. Including rotation in 1D stellar evolution models alters the structure of the star in a manner that has a significant impact on the character of multidimensional convection. Adding modest amounts of rotation to a stellar model that ignores rotation during the evolutionary stage, however, has little impact on the character of the resulting convection. Since the spatial scale and strength of convection present at the point of core collapse directly influence the supernova mechanism, our results suggest that rotation could play an important role in setting the stage for massive stellar explosions.

Supernovae (SNe) are energetic explosions that signal the end of a star's life. These events and the supernova remnants (SNRs) they leave behind play a central role in stellar feedback by adding energy and momentum and metals to the interstellar medium (ISM). Emission associated with these feedback processes, especially atomic and molecular line emission as well as thermal and nonthermal continuum emission is known to be enhanced in regions of high density, such as dense circumstellar matter (CSM) around SNe and molecular clouds (MCs). In this thesis, I begin with a brief overview of the physics of SN shocks in Chapter 1, focusing on a foundation for studying pan-chromatic signatures of interactions between SNe and dense environments. In Chapter 2, I examine an unusual SN with signatures of CSM interaction in the form of narrow lines of hydrogen (Type IIn) and thermal continuum emission. This SN appears to belong to a class of Type Ia SNe that shares spectroscopic features with Type IIn SNe. I discuss the difficulties of decomposing spectra in a regime where interaction occurs between SN ejecta and CSM, potentially confusing the underlying SN type. This is followed by a discussion of rebrightening that occurred at late-time in 𝐵 and 𝑉 band photometry of this SN, possibly associated with clumpy or dense CSM at large distances from the progenitor. In Chapter 3, I examine synchrotron emission from Cassiopeia A, observed in the 𝐾ₛ band over multiple epochs. The synchrotron emission is generally diffuse over the remnant, but there is one location in the southwest portion of the remnant where it appears to be enhanced and entrained as knots of emission in the SNR ejecta. I evaluate whether the 𝐾ₛ band knots are dominated by synchrotron emission by comparing them to other infrared and radio imaging that is known to be dominated by synchrotron emission. Concluding that they are likely synchrotron-emitting knots, I measure the magnetic field strength and electron density required for their evolution over the ~ 10 yr baseline they were observed and find 𝐵 ≈ 1.3-5.8 mG and 𝑛ₑ≈ 1,000-15,000 cm⁻³. The magnetic field strengths appear enhanced beyond values required by the adiabatic strong shock limit, arguing in favor of other forms of magnetic field amplification in the shock. In Chapter 4, I again discuss Cassiopeia A and interaction between the remnant and nearby MCs as seen at mid-infrared and millimeter wavelengths. I report detection of a SNR-MC interaction and analyze its signatures in broadened molecular lines. I extend this analysis in Chapter 5 to a large survey for SNR-MC interactions in the ¹²CO 𝐽=2-1 line. Although broadened ¹²CO 𝐽=2-1 line emission should be detectable toward virtually all SNR-MC interactions, I find relatively few examples; therefore, the number of interactions is low. This result favors mechanisms other than supernova feedback as the basic trigger for star formation. In addition, I find no significant association between TeV gamma-ray sources and MC interactions, contrary to predictions that SNR-MC interfaces are the primary venues for cosmic ray acceleration. I end this dissertation in Chapter 6 with a brief summary of my results and two extensions of this work: examining the late-time radio light curves of CSM-interacting SNe for signatures of radio synchrotron emission and dense or clumpy CSM at large distances from the progenitor and re-observing SNR-MC interactions in ¹²CO 𝐽=3-2 in order to verify the presence of shock-heated molecular gas and perform a census on the densities and temperatures of post-shock molecular gas.

On 2014 December 9.61, the All-sky Automated Survey for SuperNovae (ASAS-SN or "Assassin") discovered ASASSN-141p just similar to 2 days after first light using a global array of 14 cm diameter telescopes. ASASSN-141p went on to become a bright supernova (V = 11.94 mag), second only to SN 2014J for the year. We present prediscovery photometry (with a detection less than a day after first light) and ultraviolet through near-infrared photometric and spectroscopic data covering the rise and fall of ASASSN-141p for more than 100 days. We find that ASASSN-141p had a broad light curve (Delta m(15) (B) = 0.80 +/- 0.05), a B-band maximum at 2457015.82 +/- 0.03, a rise time of 16.941(-0.10)(+0.11) days, and moderate host-galaxy extinction (E (B - V)host = 0.33 +/- 0.06). Using ASASSN-141p, we derive a distance modulus for NGC 4666 of mu = 30.8 +/- 0.2, corresponding to a distance of 14.7 +/- 1.5 Mpc. However, adding ASASSN-141p to the calibrating sample of Type Ia supernovae still requires an independent distance to the host galaxy. Finally, using our early-time photometric and spectroscopic observations, we rule out red giant secondaries and, assuming a favorable viewing angle and explosion time, any nondegenerate companion larger than 0.34 RG(circle dot).

This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from 'Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be I >+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).

L’un des plus grands défis de la cosmologie moderne est d’expliquer l’accélération de l’expansion de l’univers dans son histoire récente. La découverte de cette accélération s’est faite grâce à des mesures de supernovae, ces dernières restant les sondes les plus puissantes pour charactériser cette accélération. Cette thèse vise à présenter l’analyse finale du Supernova Legacy Survey (SNLS) qui sera publiée en 2015. Nous commençons par présenter les fondements théoriques de la cosmologie moderne, en nous focalisant en particulier sur les défis théoriques que présente cette accélération. Nous introduisont ensuite les supernovae de type Ia (SNIa) et justifions leur usage en tant que sonde cosmologique. Par la suite, nous donnons un aperçu global de l’expérience SNLS. Nous abordons alors les aspects techniques de l’analyse. Nous commençons par l’exploration du processus de photométrie, utilisé pour la mesure des supernovae. Nous détaillons alors la nouvelle méthode de photométrie implémentée par SNLS qui évite le rééchantillonnage des images. Nous explorons aussi les simulations mise en œuvre dans le but de garantir la linéarité de la méthode au dessous de 1 pour mille. Nous explorons ensuite la procédure de calibration associée à ces mesures utilisant des étoiles de champ dont la précision de calibration atteint les 3.5 pour mille. Enfin, nous terminons avec une description détaillée de la mise en oeuvre de tous les outils présentés, afin d’extraire des paramètres cosmologiques des données. Afin d’estimer la capacité de SNLS à contraindre les paramètres cosmologiques, nous contruisons un diagramme de Hubble grâce à une analyse préliminaire des données incluant 960 supernovae, dont 450 provenant du SNLS. La combinaison de ce diagramme de Hubble avec des contraintes apportées d’autres sondes cosmologiques mène à une incertitude sur le paramètre de l’équation d’état de l’énergie noire de 0.048, la mesure la plus précise jusqu’à nos jours. / A significant open question of modern cosmology is explaining the accelerated expansion of the universe in late times. The discovery of this acceleration was made using supernova measurements, which continue to be the most significant probe with which to characterize this acceleration. This thesis concerns itself with presenting the final analysis of the Supernova Legacy Survey (SNLS) which will be published in 2015. We begin by presenting the theoretical foundations of modern cosmology, with special emphasis on the challenges presented by acceleration. We then introduce type Ia supernovae (SNIa) and motivate their use as probes of cosmic expansion. Afterwards, we give an overview of the SNLS experiment. We then move on to the technical aspects of the analysis that was carried out. We start by exploring the process of photometry, with which supernova measurements are made. Here we look at the newly implemented photometry method that avoids resampling images. We also explore simulations aimed at ensuring the method’s linearity up to less than 1 per mille. We then explain the calibration process associated with these measurements using field stars calibrated up to the 3.5 per mille level. Finally, we end with an in depth look at the cosmology analysis itself, which utilizes all the tools we have explored to extract cosmological parameters from the data. To estimate the constraining power of the SNLS experiment, we undertake a preliminary analysis of the data by constructing a Hubble diagram using 960 supernovae, of which 450 come from the SNLS. Combining this Hubble diagram with constraints from other cosmological probes leads to an uncertainty on the equation of state parameter of dark energy of 0.048, its most preciseconstraint to date.

We utilize a Poisson likelihood in a maximum likelihood statistical analysis to analyze X-ray spectragraphic data. Specifically, we examine four extragalactic supernova remnants (SNR). IKT 5 (SNR 0047-73.5), IKT 25 (SNR 0104-72.3), and DEM S 128 (SNR 0103-72.4) which are designated as Type Ia in the literature due to their spectra and morphology. This is troublesome because of their asymmetry, a trait not usually associated with young Type Ia remnants. We present \emph{Chandra X-ray Observatory} data on these three remnants, and perform a maximum likelihood analysis on their spectra. We find that the X-ray emission is dominated by interactions with the interstellar medium. In spite of this, we find a significant Fe overabundance in all three remnants. Through examination of radio, optical, and infrared data, we conclude that these three remnants are likely not "classical" Type Ia SNR, but may be examples of so-called "prompt" Type Ia SNR. We detect potential point sources that may be members of the progenitor systems of both DEM S 128 and IKT 5, which could suggest a new subclass of prompt Type Ia SNR, Fe-rich CC remnants. In addition, we examine IKT 18. This remnant is positionally coincident with the X-ray point source HD 5980. Due to an outburst in 1994, in which its brightness changed by 3 magnitudes (corrsponding to an increase in luminosity by a factor of 16) HD 5980 was classified as a luminous blue variable star. We examine this point source and the remnant IKT 18 in the X-ray, and find that its non-thermal photon index has decreased from 2002 to 2013, corresponding to a larger proportion of more energetic X-rays, which is unexpected.

Cette thèse s'intéresse à divers aspects de l'univers de Dirac-Milne, un modèle cosmologique dans lequel matière et antimatière sont présentes en quantités égales et où l'on suppose, comme pourrait le suggérer la relativité générale à travers les propriétés des solutions de Kerr-Newman, que l'antimatière possède une masse gravitationnelle active négative. Ces hypothèses permettent de s'affranchir de la nécessité d'introduire Inflation, Énergie Noire et Matière Noire, dont les mises en évidences expérimentales et les motivations théoriques font parfois défaut. La présence en quantités égales de matière de masse positive et d'antimatière de masse négative impose une évolution du facteur d'expansion linéaire par rapport au temps. Après avoir rappelé les concepts basiques de la cosmologie, certaines implications de cette évolution linéaire sont étudiées. L'étude complète de la nucléosynthèse primordiale dans le cadre de ce modèle alternatif permet de montrer qu'une production primordiale de deutérium est rendue possible par la présence d'annihilations résiduelles entre matière et antimatière à des époques précédant la recombinaison. Toutefois, ce mécanisme de production secondaire conduit à une surproduction d'hélium-3, potentiellement incompatible avec les observations. Bien que l'univers de Dirac-Milne ne présente pas d'accélération de l'expansion aux époques récentes, il est montré que ce modèle satisfait raisonnablement bien au test cosmologique des supernovae de type Ia. De même, l'échelle angulaire du premier pic acoustique des fluctuations de température du fond diffus cosmologique apparaît naturellement à l'échelle du degré. Même si l'étude complète du spectre de ces fluctuations et de la cohérence de la notion de masse négative reste encore à approfondir, ce travail pose les bases d'un modèle cosmologique original et potentiellement capable de donner une autre description de notre Univers.

L'utilisation des supernovae de type Ia comme indicateurs de distance est un pilier du modèle de concordance actuel en cosmologie. Le travail d'instrumentation présenté dans la première partie a été réalisé dans le cadre d'un projet utilisant ces objets, le satellite SNAP, qui nécessite la spatialisation d'un grand plan focal comportant des détecteurs CCD pour le visible et APS pour l'infra-rouge. Pour tester la lecture de ces détecteurs à très bas bruit, nous avons construit deux bancs de test cryogéniques et étudié en détail un ASIC analogique. La deuxième partie est l'analyse de données existantes dans le cadre de notre modèle "calorimétrique", pour améliorer l'utilisation des SN Ia comme étalons. Le programme GRATIS calcule le dépot d'énergie radioactive dans la supernova. La comparaison avec les puissances lumineuses mesurées est satisfaisante. D'autres pistes incluent l'évolution des spectres en phase tardive et l'observation d'un saut de couleur baptisé "rayon vert".

Le SuperNova Legacy Survey (SNLS) est un programme de détection et de suivi photométrique de plusieurs centaines de supernovæ de type Ia (SNe Ia) dont l'objectif est de retracer l'histoire de l'expansion cosmologique afin d'en déduire une caractérisation de la nature de l'énergie noire, c'est-à-dire une mesure de son paramètre d'état wDE. La prise de données du SNLS est arrivée à son terme en juillet 2008 après 5 ans de programme. Le travail réalisé dans le cadre de cette thèse a consisté en l'analyse de ces 5 ans de données SNLS et la photométrie des 419 SNe Ia détectées et spectroscopiquement identifiées. Pour chaque supernova, les courbes de lumière dans les bandes gMrMiMzM sont produites, calibrées et ajustées par un modèle spectrophotométrique. Une nouvelle méthode de photométrie, sans rééchantillonnage des pixels des images, est également implémentée dans le cadre de cette thèse. En préservant les propriétés statistiques des pixels, elle permet de mieux contrôler les incertitudes sur la mesure des flux, et par là même, la précision sur la mesure des paramètres cosmologiques qui s'en déduit. Les performances des deux méthodes sont testées et comparées sur les étoiles de calibration et les supernovae. Si la photométrie sans rééchantillonnage permet une estimation plus exacte des incertitudes de mesure du flux, la précision et la stabilité des deux méthodes sont quant à elles similaires. Un lot de SNe Ia de statistique et de qualité inédites est maintenant disponible pour l'analyse de cosmologie. Avec le complément de supernovæ proches de programmes extérieurs, une contrainte à 5% sur la nature du paramètre d'état de l'énergie noire est donc pour la première fois envisageable.