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).

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.

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.

Type Ia supernovae can be used as distance indicators for probing the expansion history of the Universe. The method has proved to be an efficient tool in cosmology and played a decisive role in the discovery of a yet unknown energy form, dark energy, that drives the accelerated expansion of the Universe. The work in this thesis addresses the nature of dark energy, both by presenting existing data, and by predicting opportunities and difficulties related to possible future data. Optical and infrared measurements of type Ia supernovae for different epochs in the cosmic expansion history are presented along with a discussion of the systematic errors. The data have been obtained with several instruments, and an optimal method for measuring the lightcurve of a background contaminated source has been used. The procedure was also tested by applying it on simulated images. The future of supernova cosmology, and the target precision of cosmological parameters for the proposed SNAP satellite are discussed. In particular, the limits that can be set on various dark energy scenarios are investigated. The possibility of distinguishing between different inverse power-law quintessence models is also studied. The predictions are based on calculations made with the Supernova Observation Calculator, a software package, introduced in the thesis, for simulating the light propagation from distant objects. This tool has also been used for investigating how SNAP observations could be biased by gravitational lensing, and to what extent this would affect cosmology fitting. An alternative approach for estimating cosmological parameters, where lensing effects are taken into account, is also suggested. Finally, it is investigated to what extent strongly lensed core-collapse supernovae could be used as an alternative approach for determining cosmological parameters.

Cette thèse, effectuée à l'Institut de Physique Nucléaire de Lyon (IPNL), s'inscrit dans le cadre de l'expérience SNfactory, dédiée à l'observation précise d'un grand nombre de supernovae de type Ia. Ces explosions thermonucléaires de naines blanches, très lumineuses, sont aujourd'hui les meilleures chandelles standards connues et ont de ce fait un grand intérêt pour la cosmologie.<br />Les travaux exposés ici contribuent à l'étalonnage de SNIFS, le spectrographe à champ intégral utilisé par SNfactory pour l'observation des supernovae de type Ia. Une étude des CCD a été effectuée ainsi que la collection de spectres d'étoiles de référence pour l'étalonnage en flux de l'instrument. La contribution principale a consisté en la réalisation d'un code complet pour l'extraction du spectre d'une source ponctuelle à partir du cube pré-étalonné de données. Le procédé choisi est la photométrie de PSF (Point Spread Function), nécessaire ici du fait de la petite taille du champ observé. Le flux perdu peut ainsi être évalué, et l'on atteint une qualité de mesure du flux de l'ordre du pourcent, objectif de l'expérience.

This thesis presents the CfAIR2 data set, which includes over 4000 near-Infrared (NIR) \(JHK_s\)-band measurements of 104 Type Ia Supernovae (SN Ia) observed from 2005-2011 using PAIRITEL, the 1.3-m Peters Automated InfraRed Imaging TELescope at the Fred Lawrence Whipple Observatory (FLWO) on Mount Hopkins, Arizona. While the discovery of dark energy and most subsequent supernova cosmology has been performed using optical and Ultraviolet wavelength observations of SN Ia, a growing body of evidence suggests that NIR SN Ia observations will be crucial for future cosmological studies. Whereas SN Ia observed at optical wavelengths have been shown to be excellent standardizeable candles, using empirical correlations between luminosity, light curve shape, and color, the CfAIR2 data set strengthens the evidence that SN Ia at NIR wavelengths are essentially standard candles, even without correction for light-curve shape or for reddening. CfAIR2 was obtained as part of the CfA Supernova Program, an ongoing multi-wavelength follow-up effort at FLWO designed to observe high-quality, densely sampled light curves and spectra of hundreds of low-redshift SN Ia. CfAIR2 is the largest homogeneously observed and processed NIR data set of its kind to date, nearly tripling the number of individual \(JHK_s\) band observations and nearly doubling the set of SN Ia with published NIR light curves in the literature. Matched only by the recently published Carnegie Supernova Project sample, CfAIR2 complements the large and growing set of low-redshift optical and NIR SN Ia observations obtained by the CfA and other programs, making this data set a unique and particularly valuable local universe anchor for future supernova cosmology. / Astronomy

Type Ia supernovae (SNe Ia) are currently the best probe of the expansion history of the universe. Their usefulness is due chiefly to their uniformity between supernovae (SNe). However, there are some slight variations amongst SNe that have yet to be understood and accounted for. The goal of this work is to uncover relationships between the spectral features and the light curve decline rate, [delta]m₁₅. Wavelet decomposition has been used to develop a new spectral index to measure spectral line strengths independent of the continuum and easily corrected for noise. This new method yields consistent results without the arbitrary uncertainties introduced by current methods and is particularly useful for spectra which do not have a clearly defined continuum. These techniques are applied to SN Ia spectra and correlations are found between the spectral features and light curve decline rate. The wavelet spectral indexes are used to measure the evolution of spectral features which are characterized by 3 or 4 parameters for the most complicated evolution. The three absorption features studied here are associated with sulfur and silicon and all show a transition in strength between 1 to 2 weeks after B-band maximum. Pearson correlation coefficients between spectral features and [delta]m₁₅ are found to be significant within a week of maximum brightness and 3 to 4 weeks post-maximum. These correlations are used to determine the principal components at each epoch among the set of SN spectra in this work. The variation contained in the first principal component (PC1) is found to be greater than 60% to 70% for most epochs and reaching as high as 80% to 90% for epochs with the highest correlations. The same first principal component can be used to relate spectral feature strengths to the decline rate. These relations were used to estimate a SN light curve decline rate from a set of spectra taken over the course of the explosion, from a single spectrum, or from even a single spectral feature. These relationships could be used for future surveys to estimate spectral characteristics from light curve data, such as photometric redshift.

Type Ia supernovae (SNe Ia) have proven to be extremely useful for measuring cosmological distances and were used for the discovery of the accelerated expansion of the universe. Although thousands of SNe Ia have been observed to date, many questions surrounding the physics of the explosions and the nature of their progenitor systems remain unanswered. An notable property of many SNe Ia is the relation between extinction due to dust and their colour. For example SN 2014J, the nearest SN Ia in recent years, has an extinction relation which would be very unusual to observe in the Milky Way. One possible explanation to the peculiar extinction could be the presence of circumstellar (CS) dust surrounding the explosions. Incidentally, some proposed progenitor models of SNe Ia suggest that the explosions are surrounded by shells of matter, which could account for the unusual extinction. CS gas would be ionised, if it is exposed to the intense ultraviolet (UV) radiation of a SN Ia. The research presented in this thesis focuses on the search for CS gas by observing the effects of photoionisation on absorption lines commonly detected in optical spectra. Simple models suggest that the frequently studied sodium doublet (Na I D) should significantly decrease or even disappear if the gas is in the CS environment. Conversely, the absence of variations implies that the absorbing gas clouds must be far from the explosion, in the interstellar medium (ISM). To date, few SNe Ia have been shown to have variable absorption lines, to which we have added another case with SN 2013gh. Yet, we have also shown that most observations searching for variable absorption lines have been taken at too late phases, when most CS gas will have already been ionised. Setting out to obtain the earliest possible coverage of a SN Ia with high-resolution spectra, we have been able to set strong limits on the presence of CS gas surrounding SN 2017cbv. Along with evidence from other observational methods, these results have shown that there is little matter in the CS environments of SNe Ia, suggesting that the peculiar extinction likely results from the dust properties of their host galaxy ISM. Although the progenitor question cannot be resolved by these observations, nondetections of CS gas point to models which do not deposit large amounts of matter in their surroundings. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Submitted.</p>

20 supernovae that spectroscopically match the peculiar, superluminous type Ia supernova 2003fg are studied in this project. SN2003fg is thought to have erupted at a super-Chandrasekhar mass, thus breaching the theoretical mass limit for a white dwarf. By analysing the lightcurves of these 20 supernovae, this work aims to understand what the progenitor binary systems from which the supernovae erupt looked like. A lightcurve fitting using the software snpy is performed for each supernova. Using the produced models, time of maximum luminosity, stretch and maximum magnitudes in the g-, r- and i-bands are found. It is found that subluminous supernovae might be a sign of circumstellar material surrounding the progenitor star, though some of the supernovae were superluminous and some adhered to Phillip's relationship. Substructures were found in the lightcurves, as the sampled supernovae showed clearly different behaviours in each of the three bands.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第25116号 / 理博第5023号 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)講師 LEEShiu Hang, 教授 横山 央明, 教授 前田 啓一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM