Dissertations / Theses on the topic 'Supernovae'

Massive stars are thought to end their lives with spectacular explosions triggered by the gravitational collapse of their cores. Interacting supernovae are generally attributed to supernova explosions occurring in dense circumstellar media, generated through mass-loss which characterisie the late phases of the life of their progenitors. In the last two decades, several observational evidences revealed that mass-loss in massive stars may be related to violent eruptions involving their outer layers, such as the luminous blue variables. Giant eruptions of extragalactic luminous blue variables, similar to that observed in $\eta$~Car in the 19th century, are usually labelled `SN impostors', since they mimic the behaviour of genuine SNe, but are not the final act of the life of the progenitor stars. The mechanisms producing these outbursts are still not understood, although the increasing number of observed cases triggered the efforts of the astronomical community to find possible theoretical interpretations. More recently, a number of observational evidences suggested that also lower-mass stars can experience pre-supernova outbursts, hence becoming supernova impostors. Even more interestingly, there is growing evidence of a connection among massive stars, their outbursts and interacting supernovae. All of this inspired this research, which has been focused in particular on the characterisation of supernova impostors and the observational criteria that may allow us to safely discriminate them from interacting supernovae. Moreover, the discovery of peculiar transients, motivated us to explore the lowest range of stellar masses that may experience violent outbursts. Finally, the quest for the link among massive stars, their giant eruptions and interacting supernovae, led us to study the interacting supernova LSQ13zm, which possibly exploded a very short time after an LBV-like major outburst.
Le stelle massive terminano la loro vita con spettacolari esplosioni innescate dal collasso gravitazionale del loro nucleo. Le supernove interagenti sono tipicamente associate a questo tipo di esplosioni in mezzi circumstellari densi, generati da episodi di perdita di massa durante le fasi finali dell'evoluzione dei loro progenitori. Negli ultimi due decenni, diverse evidenze osservative hanno rivelato come questi episodi siano spesso correlati ad eruzioni violente che coinvolgono gli strati esterni degli inviluppi di stelle massive, come le `luminous blue variables'. In qualche caso questi eventi sono stati osservati come `supernova impostors' (impostori), transienti che imitano il comportamento di supernove reali, ma non costituiscono l'atto finale della vita dei loro progenitori. Questi sono spesso associati alle eruzioni giganti di luminous blue variable extragalattiche. I meccanismi che innescano queste eruzioni non sono ancora del tutto compresi, nonostante il crescente numero di casi osservati abbia attirato l'attenzione della comunit\'a astronomica nel tentativo di trovare delle spiegazioni teoriche a questi fenomeni. P\'iu di recente, un certo di numero di evidenze osservative ha portato ad ipotizzare che anche stelle meno massive possano mostrare eruzioni giganti che imitano gli osservabili delle supernove interagenti. Tutto questo, unitamente alla possibile connessione recentemente proposta tra le stelle massive, le loro eruzioni giganti e alcune supernove interagenti, ha ispirato questo lavoro di ricerca, che si \'e focalizzato in particolare sulla caratterizzazione del fenomeno degli impostori e sui possibili criteri osservativi che permettono di distinguere con sicurezza le supernove interagenti dagli impostori. Inoltre, la scoperta di oggetti peculiari ci ha motivato nell'analisi dell'estremo inferiore dell'intervallo di masse interessate da episodi eruttivi violenti. La caccia al collegamento tra le stelle massive, le loro eruzioni giganti e le supernove interagenti, ha portato alla scoperta della supernova peculiare LSQ13zm, che potrebbe essere esplosa poco tempo dopo un'eruzione gigante simile a quelle osservate nelle luminous blue variables.

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<z<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 < 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.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

La presence d’inhomogénéite de matière le long de la ligne de visée d’une source lumineuseprovoque la déviation des rayons lumineux : c’est l’effet de lentille gravitationnelle. Dans cette thèse, nous etudions l’effet de lentille gravitationnelle qui affecte les supernovae détectées par le Supernova Legacy Survey et induit une dispersion supplémentaire dans leur distribution en magnitude observée. Cet effet est mis en évidence par la mesure d’une corrélation positive entre : d’une part, le résidu au diagramme de Hubble c’est-à -dire à l’ajustement de la dépendance en redshift de la magnitude de la supernova ; d’autre part, la magnification calculée en modélisant les halos galactiques présents le long de la ligne de visée. Une corrélation positive est estimée, en utilisant les données à cinq ans du Supernova Legacy Survey. Le résultat obtenu est compatible avec les résultats précédemments obtenus sur un lot de supernovae plus restreint
The presence of mass inhomogeneities along the line of sight of propagation of light fromdistant objects can induce deflection in the flight path of the photon. This phenomenon is called as gravitational lensing. Lensing can have both distortion (shear) and isotropic magnification effects on the source. We studied the effect of lensing magnification on supernova (SN) Ia in this thesis. Presence of lensing would introduce a source of contamination to the brightness distribution of the source (SN Ia in our case). Thus it also enables one to compute the lensing effect indirectly from the Hubble diagram (i.e. from the residual to the Hubble diagram). In this thesis we computed the correlation between these two effects : the Hubble residual and the computed lensing magnification for the SN by the line of sight foreground dark matter haloes. A detection of positive correlation between these two would signify the positivity of lensing signal detection. The data sample is the spectroscopic SNe Ia sample from the five years full SNLS data and the Hubble resiudals are those of the preliminary cosmology analysis performed on SNLS5 data. We obtain a signal of _ = 0.177 at 2.51_. This result is consistent with the previous SNLS three years data lensing analysis results

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.

The IceCube Neutrino Observatory consists of a lattice of 5160 photomultiplier tubes (PMTs)

which monitor one cubic kilometer of deep Antarctic ice at the geographic South Pole.

IceCube was primarily designed to detect neutrinos of energies greater than O(100 GeV).

Due to subfreezing ice temperatures, the photomultipliers' dark noise rates are particularly

low which enables IceCube to search for neutrinos from galactic supernovae by detecting

bursts of MeV neutrinos emitted during the core collapse and for several seconds following.

For that purpose, a dedicated online supernova DAQ system records the total number of hits

in the detector, without any further information from the PMTs, and generates supernova

candidate triggers in case of a significant detector rate enhancement. A new feature to the

standard DAQ, called HitSpooling, was implemented in IceCube during this thesis. The

HitSpooling system is implemented in the standard DAQ system and buffers the complete

raw data stream of the photomultipliers for several hours or days. By reading out time periods

of HitSpool data around supernova candidate triggers, generated by the online supernova

DAQ system, we overcome the limitations of the latter and have access to the entire information

of the detector in case of a supernova. Furthermore, HitSpool data is a powerful

source for studying and understanding the noise behavior of the detector as well as background

processes coming from atmospheric muons. The idea of HitSpooling was developed in the

scope of this thesis and is the basis of the work at hand. The developed interface between the

standard DAQ and the supernova DAQ system is presented. The correlated dark noise component

in optical modules of IceCube is quantified for the first time and possible explanations

are discussed. The possibility of identifying triggering and subthreshold atmospheric muons

in HitSpool data and subtracting them from a possible supernova signal is analyzed. Furthermore,

the conversion from HitSpool data to supernova DAQ type data was developed

which allows for a comparison of both data types with respect to lightcurves and significances

of selected supernova candidate triggers.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

En el presente trabajo se han conectado unos fenómenos pertenecientes al campo de la observación (las supernovas de tipo 1, SN 1) con los procesos físicos que tienen lugar en fases evolutivas avanzadas de los sistemas binarios compactos en los que hay una enana blanca de carbono-oxigeno que acreta materia. El estudio llevado a cabo muestra que el fenómeno observacional de las SN 1 es la consecuencia última de que dichos procesos se verifiquen bajo unas condiciones específicas y que es posible reproducir las características más notables de las supernovas de tipo 1 en el escenario a que nos referimos si se considera de forma realista las condiciones físicas existentes en el interior de la enana que da origen al fenómeno. El trabajo ha sido estructurado de la forma que se indica a continuación: El primer capítulo se dedica a analizar las observaciones de SN 1 disponibles con objeto de establecer las restricciones que deben imponerse a los modelos que se formulen así como a los resultados que de ellos se obtengan. En el segundo capítulo se discuten los diversos modelos que se han ido realizando hasta la fecha para explicar el fenómeno de las SN I, señalando los problemas que plantean y que los hacen inviables a la hora de dar una explicación totalmente satisfactoria del mismo. Se acaba con la presentación de las relaciones dimensionales obtenidas a partir de los modelos analíticos de Arnett, de gran importancia para entender el origen de las dificultades con que tropiezan los modelos teóricos de formulación más reciente. Posteriormente, se presenta un escenario general que sirve de base para el desarrollo de las supernovas de tipo 1: los sistemas binarios compactos que poseen enanas blancas masivas las cuales han desarrollado un núcleo Sólido de carbono-oxígeno. En el marco del citado escenario, se construyen modelos para simular numéricamente las curvas de luz de las SN 1. Los modelos se han formulado teniendo en cuenta las relaciones dimensionales de Arnett y resultados previos de cálculos sobre explosión de objetos compactos. La integración numérica de las ecuaciones de conservación y de transporte bajo unas hipótesis físicas bastante generales permite obtener la evolución temporal de cada modelo y su comparación con 105 observables. Todo ello, marco astrofísico y método de construcción de los modelos, se expone en el tercer capítulo del trabajo. El capítulo cuarto recoge y analiza los resultados de los cálculos que se han llevado a cabo. Se destacan en él los efectos que tiene el considerar como progenitores de las supernovas enanas blancas totalmente fluidas o, por el contrario, con un núcleo Sólido. Se muestra mediante dos secuencias de modelos, una para cada caso, las consecuencias observacionales a que da lugar el que la explosión deje o no un residuo ligado, en especial en lo que se refiere a poder reproducir el efecto Pskovski-Branch. Adicionalmente, se indican las incertidumbres que padecen los modelos y se estudian las consecuencias que supondría cambiar el valor de algunos parámetros no bien conocidos. Asimismo, se discuten las implicaciones cosmológicas del modelo de explosión de supernova que se presenta en lo relativo a su compatibilidad con determinados valores de la constante de Hubble. Finalmente, se indican las posibles vías de continuación del trabajo.

Supernovae are cosmic explosions of cataclysmic proportion that signify the death of a star. While being interesting phenomena in their own right, their brightness also make them excellent probes of the early universe. Depending on the type of the progenitor star and the origin of the explosion different subjects can be investigated. In this dissertation the work I have done on the detection, characterisation and rate measurements of supernovae in the Stockholm VIMOS Supernova Search is presented. We have discovered 16 supernovae that exploded billions of years ago (or, equivalently, at high redshift, z). The observed brightness and colour evolution have been used to classify the supernovae into either thermonuclear (type Ia) or core collapse (type II) supernovae. The accuracy of the classification code is high, only about 5% of the supernovae are mistyped, similar to other codes of the same kind. By comparing the observed frequency of supernovae to simulations the underlying supernova rate at these high redshifts have been measured. The main result reported in this thesis is that the core collapse supernova rate at high redshift matches the rates estimated from looking at the star formation history of the universe, and agree well with previous studies. The rate of Ia supernovae at high redshift have been investigated by several projects, our results show a somewhat higher rate of Ia supernovae than expected. Proper estimates of the systematic errors of rate measurements are found to be very important. Furthermore, by using novel techniques for reducing and stacking images, we have obtained a galaxy sample containing approximately 50,000 galaxies. Photometric redshifts have been obtained for most of the galaxies, the resulting accuracy below z=1 is on the order of 10%. The galaxy sample has also been used to find high redshift sources, so called Lyman Break Galaxies, at z=3-5.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript. Paper 4: Manuscript.

The study of supernovae (SNe) has greatly advanced in recent years, in particular due to the successes of wide-field transient surveys. The ever-increasing quantity of data has led to the discoveries of a large number of peculiar SNe with extreme properties, which both challenge and illuminate the current understanding of massive star evolution. In this thesis, I present detailed analyses of three SNe, each of which can be considered to be extreme in some way. The analysis highlights the multiple competing physical effects that the properties of massive stars at the end of their lives have on the resulting explosion. The understanding of this is one of the key goals of SNe research.

À la fin de leur vie, les étoiles massives explosent et produisent un phénomène appelé supernova. Tout commence lorsque les réactions de fusion au cœur de l'étoile s'épuisent. Le cœur de l'étoile s'effondre jusqu'à devenir si dense que les forces nucléaires contrebalancent la gravité, créant un rebond. Le cœur interne donne alors naissance à un astre compact, une protoétoile à neutrons (PNS) d'un rayon de ~50 km à sa formation.L'onde de choc générée par ce rebond se propage alors vers les couches extérieures, continuant à s'effondrer. Cependant, l'énergie de ce choc n'est pas immédiatement suffisante pour qu'il atteigne directement la surface de l'étoile. Il devient stationnaire à un rayon de ~ 200 km. L'explosion de l'étoile en supernova dépend de la capacité de ce choc à être relancé pour atteindre la surface de l'étoile. L'interaction entre la matière et les neutrinos joue un rôle essentiel dans cette dynamique. Les neutrinos émis par la PNS peuvent être absorbés par la matière dense se trouvant sous le choc. Le chauffage qui en résulte induit un gonflement du choc. Le développement d'instabilités hydrodynamiques affecte l'efficacité d'absorption des neutrinos sous l'onde de choc stationnaire. Parmi les instabilités, la convection est favorisée par l'établissement d'un gradient négatif d'entropie. Les mouvements convectifs prolongent l'exposition de la matière au flux de neutrinos. D'autre part, l'instabilité du choc d'accrétion stationnaire (SASI) est due à un cycle entre des ondes acoustiques et l'advection des perturbations d'entropie et de vorticité générée par la déformation du choc.Par sa géométrie spirale, elle permet une augmentation locale de la densité et augmente aussi la probabilité d'interaction des neutrinos avec la matière.Dans cette thèse, nous présentons une analyse linéaire (analytique et numérique) de ces deux instabilités, permettant d'établir les domaines de paramètres pour lesquels chacune des instabilités domine la dynamique du flot. Nous étudions ensuite l'impact de la rotation sur ces domaines. Cet effet de la rotation sur les instabilités est encore peu étudié et est une question ouverte dans la communauté. En absence de rotation, l'intensité du chauffage de la matière par les neutrinos, évaluée à travers un paramètre χ de comparaison du temps de flottaison et du temps d'advection, permet la distinction entre le domaine de SASI et le domaine convectif. Nous démontrons les lacunes de ce critère et proposons une autre méthode, plus générale, afin de déterminer le seuil de croissance de la convection. Contrairement aux résultats trouvés par Foglizzo et al. (2006), nous montrons que la transition d'un domaine SASI à un domaine convectif ne se fait pas pour une valeur seuil χ ∼ 3 mais sur un domaine de chauffage tel que χ ∈ [3, 4]. Nous présentons ensuite une analyse de l'influence de la rotation sur la croissance linéaire de ces instabilités. Pour des rotations lentes, le critère d'instabilité fondé sur le paramètre χ diminue. Si la rotation excède 10% de la rotation Képlérienne à la surface de la PNS, alors des modes mixtes SASI/convection/rotation apparaissent à grande échelle. Pour les rotations fortes (>30% de la rotation Képlérienne à la surface de la PNS), l'influence du paramètre χ sur le taux de croissance et sur la fréquence du mode le plus instable devient négligeable. Cette faible dépendance indique que la convection ne joue alors plus de rôle dans l'instabilité dominante qui est d'origine rotationnelle. Dans ce régime, l'interprétation des fréquences mesurées en ondes gravitationnelles peut être facilitée car la fréquence du mode dominant est directement liée au taux de rotation du cœur de l'étoile
At the end of their lives, massive stars explode and produce a phenomenon called a supernova. It begins when the fusion reactions in the core of the star run out of fuel. The core of the star collapses until it becomes so dense that the nuclear forces counteract the gravity, creating a rebound. The inner core then gives rise to a compact star, a protoneutron star (PNS) with a radius of ~50 km at its formation.The shock wave generated by this bounce then propagates towards the collapsing outer layers. However, the energy of this shock is not enough for it to reach the star's surface directly. It becomes stationary at a radius of ~ 200 km. The explosion of the star into a supernova depends on the ability of this shock to be revived and reach the star's surface. The interaction between matter and neutrinos plays an essential role in these dynamics. Neutrinos emitted by the cooling PNS can be absorbed by the dense matter beneath the shock. The resulting heating induces a swelling of the shock.The development of hydrodynamic instabilities affects the absorption efficiency of neutrinos under the stationary shock wave. Among these instabilities, convection is favoured by the establishment of a negative entropy gradient. Convective motions prolong the exposure of matter to the neutrino flux.On the other hand, the stationary accretion shock instability (SASI) is due to a cycle between acoustic waves and the advection of entropy and vorticity perturbations, generated by the shock deformation. By its spiral geometry, it allows a local increase of the density which increases the probability of interaction of neutrinos with matter.In this thesis, we present a linear analysis (analytical and numerical) of these two instabilities, allowing us to establish the parameter domains for which each instability dominates the flow dynamics. We also investigate the impact of rotation on these domains. The effect of rotation on these instabilities is still poorly known and is an open question in the supernova community.In the absence of rotation, the intensity of neutrino heating, evaluated through χ ∼ 3 parameter comparing the flotation time and the advection time, allows the distinction between the SASI domain and the convective domain. We demonstrate the shortcomings of this criterion and suggest another, more general, criterion to determine the convective growth threshold. Contrary to the results found by Foglizzo et al. (2006}, we show that the transition from SASI to convection does not occur for a threshold value of χ ∼ 3 but on a heating domain such that χ ∈ [3, 4]. We then present an analysis of the influence of rotation on the linear growth of these instabilities. For slow rotations, the instability criterion based on the χ parameter decreases. If the rotation exceeds 10% of the Keplerian rotation at the PNS surface, then mixed SASI/convection/rotation modes appear at large scales. For strong rotations (>30% of the Keplerian rotation at the PNS surface), the influence of the χ parameter on both the growth rate and the frequency of the most unstable mode becomes negligible. This weak dependency indicates that convection no longer plays a role in the dominant instability, which is of rotational origin. In this regime, the interpretation of the measured gravitational wave frequencies can be facilitated because the frequency of the dominant mode is directly related to the rotation rate of the star's core

Les supernovae de type Ia (SNe Ia) sont aujourd'hui un outil puissant en cosmologie pour étudier l'accélération de l'expansion de l'univers. Utilisées comme chandelles standard, elles permettent de contraindre l'équation d'état de l'énergie noire à travers un diagramme de Hubble. La spectroscopie est une étape essentielle à la construction de ce diagramme à la fois pour s'assurer que les objets sont bien des SNe Ia et déterminer leur décalage vers le rouge, mais également pour mieux comprendre leurs propriétés physiques et ainsi réduire les incertitudes systématiques qui limitent l'utilisation des SNe Ia en cosmologie. Dans ce cadre, je constitue un nouvel échantillon de spectres de SNe Ia mesurés au Very Large Telescope (VLT) pour l'expérience SuperNova Legacy Survey (SNLS). Ce lot de SNe Ia rejoint celui déjà existant pour constituer l'échantillon final de spectres VLT des SNe Ia SNLS. En plus d'être intégré au diagramme de Hubble pour les analyses cosmologiques, ce lot spectroscopique peut tre utilisé pour tester si les propriétés des SNe Ia évoluent avec le décalage vers le rouge. J'aborde cette question fondamentale pour la cosmologie en utilisant à la fois le nouveau lot de spectres VLT de SNe Ia lointaines et celui des objets proches de l'expérience Nearby SuperNova Factory (SNF). Ces deux lots de spectres sont également une riche source d'information pour mieux connaître les SNe Ia et comment les standardiser. Je les confronte pour cela avec divers modèles de formations de SNe Ia afin de déterminer les zones ou paramètres discriminants qui permettraient d'améliorer les modèles pour reproduire les observations et la variabilité des SNe Ia
Type Ia supernovae (SNe Ia) are a powerful tool in cosmology today to study the acceleration of the universal expansion. Using as standardisable candles, they allow us to constrain the dark energy equation of state via a Hubble diagram. The spectroscopy is essential to build this diagram, on the one hand to secure the type of SNe Ia and estimate the redhsift, and on the other hand for a better knowledge of their physical properties to reduce the systematic uncertainties which limit the use of SNe Ia for cosmological works. In this context, I build a new sample of SN Ia spectra measured by the Very Large Telescope (VLT) for the SuperNova Legacy Survey (SNLS) experiment. These SN Ia data complete the existing sample to constitute the final VLT spectroscopic dataset of the SNLS. In addition to the inclusion in the Hubble diagram for cosmological analysis, this spectroscopic sample can be used to test if SNe Ia properties evolve with the redshift. I investigate this fundamental question for cosmology using the new VLT spectra sample of distant SNe Ia and the nearby object of the Nearby SuperNova Factory (SNF) experiment. These two samples are also a rich source of physical information for a better knowledge of SNe Ia and a better standardisation. For this purpose, I compare these data with various SNe Ia formation models to identify discriminant spectral area or parameters in order to constrain and improve the models to reproduce the observations and the SNe Ia variability

Visando aprimorar as medidas de distâncias cosmológicas feitas com a observação de supernovas de tipo Ia (SNIas), nós realizamos dois estudos: primeiro, verificamos as relações entre as propriedades das SNIas e de seus ambientes; segundo, avaliamos os dados de supernovas que poderiam ser obtidos com um mapeamento (survey) fotométrico do céu em filtros de banda estreita. Na primeira parte deste trabalho, nós utilizamos dados do Sloan Digital Sky Survey para confirmar as relações publicadas na literatura entre as propriedades das SNIas e a taxa de formação estelar de suas galáxias hospedeiras: SNIas em galáxias passivas tendem a ser mais breves, mais luminosas após correções, e sua cor influencia menos a sua magnitude quando comparadas a SNIas em galáxias ativas. Nós então analisamos SNIas em aglomerados ricos de galáxias e concluímos que elas são ainda mais breves do que a SNIa média em galáxias passivas. Essa característica está relacionada com a idade mais alta das galáxias passivas em ambientes densos e com a preferência dessas galáxias em hospedar SNIas bastante breves. As demais características das SNIas foram consideradas compatíveis com SNIas de campo dentro da precisão alcançada. Esse tipo de estudo deve impactar a determinação de distâncias uma vez que, em diversos casos, SNIas em redshifts diferentes habitam ambientes diferentes. O segundo tema desta tese trata de estudar as características de um novo método fotométrico aplicado às supernovas: o imageamento em filtros de banda estreita. Utilizando simulações de fotometria e tomando como base o projeto Javalambre Physics of the accelerating universe Astrophysical Survey (J-PAS), mostramos que um mapeamento realista em filtros de banda estreita é capaz de produzir amostras massivas de SNIas em redshifts intermediários (0 < z < 0;5) com baixa contaminação (3% ou menos), com um redshift fotométrico altamente preciso (sz =0;005) e com boa precisão na parametrização de suas curvas de luz. Além disso, filtros de banda estreita são capazes de resolver quase todas as características espectrais das supernovas. Junto com a rica informação que esse mapeamento pode prover sobre as galáxias observadas, esse tipo de projeto deve trazer contribuições significativas para o melhor entendimento das supernovas e das relações com seus ambientes.
Aiming at improvements in cosmological distance measurements performed with type Ia supernovae (SNe Ia) observations, we carried out two studies: first, we analyzed the relationships between the properties of SNe Ia and those of their environments; second, we assessed what kind of SNe data could be attained by a photometric survey using narrowband filters. In the first part of this work we used data from the Sloan Digital Sky Survey to confirm previously reported relations between SNe Ia properties and their hosts star formation rate: SNe Ia in passive galaxies tend to be briefer, more luminous after corrections and their colors do not impact their magnitudes as much when compared to SNe Ia in active galaxies. We then analyzed the properties of SNe Ia inside rich galaxy clusters and concluded that they are even briefer than the average SNe Ia in passive galaxies. This characteristic is related to the older age of passive galaxies in dense regions and their preference for hosting very brief SNe Ia. Other properties of these SNe Ia were considered compatible under the precision attained. This kind of study may influence distance determinations since, in many cases, SNe Ia at different redshifts populate different environments. On the second part of this work we studied the characteristics of a new photometric method applied to supernovae: the narrowband filter imaging of the sky. Using photometry simulations and taking the Javalambre Physics of the accelerating universe Astrophysical Survey (J-PAS) project as our fiducial survey, we showed that a realistic narrowband survey is capable of producing massive SNe Ia samples at intermediate redshifts (0 < z < 0;5) with low contamination rate (3% or less), a highly precise photometric redshift (sz = 0;005) and a good precision on their light curve parametrization. Moreover, narrowband filters are able to resolve almost every supernova spectral feature. Together with the rich galaxy information this kind of survey can provide, it should present significant contributions to the better understanding of supernovae and their relationships with their environments.

Grace a leur luminosite importante, les supernovae sont detectees a des distances cosmologiques, et sont de ce fait des outils particulierement interessants pour la cosmologie. L'homogeneite relative des supernovae de type ia permet de les utiliser comme chandelles standard pour determiner les distances jusqu'a un decalage vers le rouge egal a 1. La precision des distances mesurees est augmentee par l'utilisation de relations d'intercalibration etablies sur des supernovae de type ia proches, decouvertes par la technique d'examen visuel de plaques photographiques. Ainsi, en portant les distances des supernovae proches dans un diagramme distance - decalage vers le rouge, dit diagramme de hubble, il est possible d'estimer la valeur de la constante de hubble qui mesure la vitesse d'expansion de l'univers. En comparant dans ce meme diagramme les supernovae proches aux supernovae lointaines, decouvertes par soustraction d'images numeriques ccd, on mesure le parametre de densite de matiere l'univers ainsi que la constante cosmologique reduite. L'obtention d'un lot important de supernovae proches detectees par des techniques de soustraction d'images ccd permettrait de comparer dans le diagramme de hubble des supernovae decouvertes par des methodes semblables. De plus, l'efficacite de detection d'une telle recherche est calculable : il est alors possible d'evaluer les relations d'intercalibration sur un echantillon du supernovae pour lesquelles les biais de detection sont connus et quantifies. Pour ces raisons, le projet eros, qui utilise un telescope de 1-m dedie au foyer duquel sont montees deux cameras ccd grand champ de un degre carre chacune, consacre 10% de son temps d'observation a une recherche de supernovae proches, qui fait l'objet de cette these. La conception et la mise en uvre de la recherche de supernovae d'eros est decrite ici en detail. Nous utilisons une methode de comparaison de deux images d'un meme champ du ciel par soustraction, les supernovae apparaissant comme des sources ponctuelles sur l'image soustraite obtenue. Le traitement des champs des champs utilises pour la recherche de supernovae est automatise. Le calcul de l'efficacite de detection des supernovae est effectue par simulation monte-carlo. Le comptage de galaxies realise sur les champs de recherche est compare aux comptages publies et theoriques. Le decalage vers le rouge de chaque galaxie est estime par une loi de probabilite dependant de sa magnitude apparente : la pertinence de cette methode est prouvee utilisant les mesures de decalage vers le rouge du relevee a grand champ the las campanas redshift survey, dont une partie des champs sont communs aux notres. La dependance de l'efficacite en fonction des conditions d'observation, des coupures de l'analyse et des caracteristiques de la galaxie hote ou des supernovae simulees y est etudiee. La distribution en decalage vers le rouge des supernovae detectees predite par la simulation est confrontee a celle des supernovae effectivement decouvertes, et au calcul theorique. Le calcul de l'efficacite se conclue par une estimation du taux d'explosion de supernovae. Les differentes sources d'erreurs, statistiques et systematiques, sont precisees.

This Thesis is focused on a photometric and spectroscopic study of four Type IIn supernovae (i.e. SN 20 06gy, 2007bt, 2007bw and 2008fz), which are among the brightest supernovae (SNe) ever detected. They belong to the sample of overluminous or Very Luminous SuperNovae (VLSNe) which currently includes other 3-4 well studied events. Their absolute luminosity at maximum, MV < -20 is much higher than any other previous supernovae, either core-collapse and or thermonuclear. Their huge brightness (> 10^(51)erg) are emitted in the first »200 days) link these events to massive or supermassive progenitors, which experi- enced extreme mass-losses during their last stages of evolution. However, other explosion mechanisms or sources of energy are being investigated; the debate on their nature is still open. The first object discussed in this Thesis is SN 2006gy, which is one the most debated supernovae ever. Contrary to typical IIn SNe, this event did dot show any strong x-rays or radio emission near the epoch of maximum. This has lead to consider other feasible non-standard sources of energy beyond interaction. In this thesis, the evolution of multiband light curves, the pseudo-bolometric (BVRI) light curve and an extended spectral sequence are presented and used to derive constraints on the origin and evolution of the nature of the SN. Its light curve is characterized by a broad, bright (MR = -21.7 at about 70 days) peak, followed by a rapid luminosity fading which turns into a slower decline by day 180. At late phases (> 237 days), because of the large lu- minosity drop (> 3 mag), only upper visibility limits are obtained in the B, R and I bands. In the near-infrared, two K-band detections on days 411 and 510 possibly indicate dust formation or IR echoes scenarios. At all epochs the spectra are characterized a multicomponent Halpha profile, without any P-Cygni. By means of a semi-analytical code, the light curve in the first 170 days is found to be consistent with the explosion of a compact progenitor (R (6 -8 x 10^(12) cm, Mej =5 -14Msol), whose ejecta collided with massive (6 - 10Msol¯), opaque clumps of previously ejected material. These clumps do not completely obscure the SN photosphere, so that at its peak the luminosity is due both to the decay of 56Ni and to interaction with the circumstellar medium (CSM). After 170 days spectroscopic and photometric similarities are found between SN 2006gy and bright, interaction-dominated SNe (e.g. SN 1997cy, SN 1999E and SN 2002ic). This suggests that ejecta-CSM interaction plays a key role in SN 2006gy about 6 to 8 months after maximum, sustaining the late-time-light curve. Alternatively, the late luminosity may be related to the radioactive decay of 3Msol of 56Ni. In this scenario, a supermassive star is not required to explain the observational data, nor is an extra-ordinarily large explosion energy. For the SNe 2007bt, 2007bw and 2008fz UBVRI light curves and an extended spectral sequence are also presented. Analogies and differences are highlighted, both among each other and with respect to the sample of VLSNe from the literature. Photometrically, it is shown that the light curves of SNe 2007bt and 2007bw are substantially dfferent from that of SN 2008fz, evolving more slowly, being redder at the earlier phases and decaying with a rate consistent with that pre- dicted by the radioactive decay of 56Co. On the contrary, the photometric evolution of SN 2008fz is reminiscent to the light curves of IIL SNe, showing a short peak followed by a steep decline. Spectroscopically the three events are characterized by high-velocity (up to 12000km/s), slowly-decelerating emission lines. The spectra of the SNe 2007bt and 2007bw are dominated by Balmer lines, overimposed on a relatively °at continuum (TBB = 6000 ¡ 7000 K); an asymmetry in the early profile of Halpha is observed, slowly disappearing with time. Measurements of the narrow components of Halpha in SN 2007bt indicate CSM speed of 320 km/s , which are only consistent with the winds surrounding luminous blue variable (LBV) stars. The early spectra of SN 2008fz are found to be similar to SN 2006gy; however, they show higher temperatures (TBB=14000 K) and a more rapid evolution. For the three events, the energetic, luminosity, initial radius (> 10^(15)cm) and the kinematic derived from the analysis of the light curves and spectra could be reproduced by the conversion of kinetic energy into radiation by a clumpy CSM which is hit by the energetic SN ejecta, similarly to what was proposed for SN 2006gy. For SNe 2007bt and 2007bw the asymmetry in the Halpha line can be explained if a massive (>10 Msol) clumpy CSM lies face-on in the direction of the observer. The asymmetry in the CSM distribution around the star could be due by a binarity fefect in the progenitor system, or asymmetric mass ejection of a single star. For SN 2008fz the rapid expansion of the black-body radius favor a less massive CSM ( 1Msol), which is efficiently warmed up and accelerated by the high-velocity SN ejecta. Because of the relatively small mass in the CSM/shell, the photon diffusion time is smaller than that calculated for SN 2006gy, and the radiated energy plummets rapidly as the light curve. As for the case of SN 2006gy, these scenarios have the advantage that they do not involve any exotic explosion mechanism for these VLSNe. However, other scenarios could be consistent with their photometric evolution. Among these, the possibility of a pair-instability explosion cannot be excluded. This and other likely hypothesis proposed by other authors are discussed.
Questa Tesi si incentra sullo studio fotometrico e spettroscopico di quattro su pernovae (SNe) di tipo IIn (cioµe SN 2006gy, 2007bt, 2007bw e 2008fz), che sono tra le supernovae più brillanti mai scoperte. Infatti appartengono alla classe delle SNe iperluminose o Very Luminous SuperNovae (VLSNe, supernovae molto brillanti), che al momento include altri 3-4 oggetti ben studiati. La loro luminosità assoluta all'epoca del massimo, MV < -20, è superiore rispetto a qualsiasi altro evento, sia di natura termonucleare che di collasso del core. L'enorme luminosità emessa (> 10^(51)erg nei primi 200 giorni) associa questi eventi a progenitori massicci o supermassicci, che hanno subito fenomeni di perdita di massa estremi durante le loro fasi evolutive finali. Comunque, al momento si stanno studiando anche altri meccanismi o possibili fonti di energia, e il dibattito sulla natura di questi eventi è tuttora aperto. Il primo oggetto discusso è la SN 2006gy, che è una delle supernovae più dibattute in assoluto. Contrariamente alle tipiche IIn, essa non mostrava alcuna emissione X o radio all'epoca del massimo di luminosità. Questo ha portato a considerare altre possibili sorgenti di energia oltre all'interazione. In questa Tesi, l'evoluzione delle curve di luce multibanda, la curva di luce pseudo-bolometrica e una sequenza di spettri vengono studiati per ricavare delle infor- mazioni sull'evoluzione e sulla natura della supernova e del progenitore. La curva di luce µe caratterizzata da un picco ampio e luminoso (MR = -21.7 a circa 70 giorni), seguito da un declino di luminosità veloce, il quale si assesta su un declino piµu lento, a circa 180 giorni. A fasi avanzate (>237 giorni), a causa del forte indebolimento della luminosità (>3 mag) vengono ricavati solo dei limiti ottici nelle bande B, R ed I. Nel vicino infrarosso, due detection nella banda K' indicano una possibile presenza di regioni di formazione di polvere, o eventualmente di echi infrarossi. A tutte le epoche gli spettri sono caratterizzati dalla presenza di pro¯li di righe a multi-componente, senza però alcun pro¯lo P-Cygni. Tramite un codice semi-analitico si trova che la curva di luce nei primi 170 giorni è consistente con l'esplosione di un progenitore compatto (R = 6-8 x 10^(12)cm, Mej = 5-14Msol), le cui ejecta collidono con dei clumps massicci (6-10 Msol) e opachi di materiale espulso precedentemente. Tali clumps non oscurano completamente la fotosfera della supernova, cosicché all'epoca del picco la luminosità è dovuta sia al decadimento radioattivo del 56Ni che all'interazione con il mezzo circumstellare. Vengono inoltre evidenziate, a partire da circa 170 giorni, delle analogie fotometriche e spettroscopiche tra la SN 2006gy e un gruppo di supernovae interagenti (cioè SN 1997cy, 1999E e 2002ic). Ciò suggerisce che l'interazione tra ejecta e CSM gioca un ruolo importante anche nella SN 2006gy a circa 6-8 mesi dal massimo, sostenendo la curva di luce a fasi avanzate. In alternativa, la luminositµa a queste fasi potrebbe essere dovuta al decadimento radioattivo di 3Msol di 56Ni. Questo scenario non richiede la presenza di una stella supermassiccia o di un'energia straordinariamente grande per spiegare i dati osservativi. Anche per le supernovae 2007bt, 2007bw e 2008fz vengono presentate delle curve di luce UBVRI e una sequenza di spettri estesa. Vengono messe in luce analogie e differenze tra tali supernovae e tra le VLSNe in letteratura. Dal punto di vista fotometrico si mostra che le curve di luce delle SNe 2007bt e 2007bw differiscono sostanzialmente da quella della SN 2008fz, poiché evolvono più lentamente, sono piµu rosse a fasi iniziali e decadono ad un tasso consistente con quello predetto dal decadimento del 56Co. Spettroscopicamente i tre eventi sono caratterizzati da righe di emissione ad alte velocità, ¯fino a 12000 km/s . Gli spettri delle supernovae 2007bt e 2007bw sono dominati dalle righe di Balmer su un continuo relativamente piatto (TBB = 6000-¡ 7000 K). Inoltre viene osservata un'asimmetria nel profilo iniziale di Halpha, che però si indebolisce col tempo. Dalla misura della componente strette di Halpha nella SN 2007bt si ricavano velocità di 320 km/s , le quali sono consistenti solo con i venti di stelle LBV (luminose, blu, variabili). Si trova inoltre che i primi spettri della SN 2008fz sono consistenti con quelli della SN 2006gy; tuttavia, essi indicano temperature maggiori (TBB = 14000 K) ed un'espansione piµu rapida. Per i tre eventi, l'energia in gioco, la luminositµa, il raggio iniziale (> 10^(15)cm) e la cinematica derivati dall'analisi delle curve di luce e degli spettri potrebbe essere riprodotta dalla conversione di energia cinetica in radiazione da parte di un mezzo circumstellare ricco di clumps, il quale viene raggiunto dalle ejecta energetiche della supernova, similmente a quanto supposto per SN 2006gy. Per le SNe 2007bt e 2007bw l'asimmetria del pro¯lo di Halpha può essere spie- gata se un mezzo massiccio (>10 Msol ) ricco di clumps si trova esattamente davanti all'osservatore, perpendicolarmente alla linea di vista. L'asimmetria nella distribuzione del mezzo circumstellare potrebbe essere dovuta ad effetti di binarietà del sistema del progenitore, o ad espulsioni di materiale asimmetriche in una stella singola. Per la SN 2008fz la rapida espansione del raggio iniziale di corpo nero tende a favorire un mezzo meno massiccio (> 10Msol), il quale viene riscaldato ed accelerato efficientemente dalle ejecta ad alta velocità. A causa della massa relativamente piccola del mezzo, il tempo di diffusione dei fotoni inferiore di quanto calcolato per la SN 2006gy, cosicché l'energia radiativa diminuisce rapidamente, come la curva di luce. Come nel caso della SN 2006gy, il vantaggio di questi scenari è che non involvono alcun meccanismo di esplosione esotico. Tuttavia, la loro evoluzione fotometrica può essere consistente anche con altri scenari. Tra questi, anche l'esplosione di una supernova di instabilità di coppia non può essere esclusa. Questi ed altri scenari vengono discussi nel capitolo conclusivo.

A sample of 9 small-diameter radio sources has been selected from the Molonglo Galactic Plane Survey (MGPS) and observed with the Australia Telescope Compact Array (ATCA) in the radio recombination line (RRL) at 5 GHz, in a search for young Galactic SNRs. Since the RRL emission is an unambiguous indicator of a thermal source, this method has been used to eliminate HII regions from the selected sample. In addition, the IRAS and MSX infrared data and spectral index measurements have been combined with the RRL studies to distinguish thermal and non-thermal sources in the selected sample. One source (G282.8-1.2) is identified here as a possible new young Galactic supernova remnant, based on its relatively weak infrared emission, steep radio spectrum and possible x-ray emission. However, the ATCA data are inconclusive and further studies are needed to confirm this result. Radio recombination line emission (H107 alpha) has been detected in 3 of the selected sources, eliminating them from the sample of SNR candidates. In addition, the parameters of the RRL emission from the identified HII regions have been used to estimate their properties. The RRL data are inconclusive for the remaining low brightness, extended sources in the sample. However, some of these sources are likely to be thermal HII regions according to the infrared and spectral index data. The selected method for distinguishing thermal and non-thermal Galactic radio sources seems promising. The selected ATCA configuration was appropriate for imaging relatively bright, compact sources, but a slightly modified observing technique is needed to successfully image low surface brightness, extended sources.

A sample of 9 small-diameter radio sources has been selected from the Molonglo Galactic Plane Survey (MGPS) and observed with the Australia Telescope Compact Array (ATCA) in the radio recombination line (RRL) at 5 GHz, in a search for young Galactic SNRs. Since the RRL emission is an unambiguous indicator of a thermal source, this method has been used to eliminate HII regions from the selected sample. In addition, the IRAS and MSX infrared data and spectral index measurements have been combined with the RRL studies to distinguish thermal and non-thermal sources in the selected sample. One source (G282.8-1.2) is identified here as a possible new young Galactic supernova remnant, based on its relatively weak infrared emission, steep radio spectrum and possible x-ray emission. However, the ATCA data are inconclusive and further studies are needed to confirm this result. Radio recombination line emission (H107 alpha) has been detected in 3 of the selected sources, eliminating them from the sample of SNR candidates. In addition, the parameters of the RRL emission from the identified HII regions have been used to estimate their properties. The RRL data are inconclusive for the remaining low brightness, extended sources in the sample. However, some of these sources are likely to be thermal HII regions according to the infrared and spectral index data. The selected method for distinguishing thermal and non-thermal Galactic radio sources seems promising. The selected ATCA configuration was appropriate for imaging relatively bright, compact sources, but a slightly modified observing technique is needed to successfully image low surface brightness, extended sources.

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

Orientadores: Marcelo Moraes Guzzo, Renata Zukanovich Funchal
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-06T18:49:31Z (GMT). No. of bitstreams: 1 SanchezVega_BruceLehmann_M.pdf: 867356 bytes, checksum: 7ef0ed6b2a81cab96ae23751d7ad2efa (MD5) Previous issue date: 2006
Resumo: Neste trabalho estudamos os decaimentos não radiativos de neutrinos de Majorana, via bósons sem massa, no vácuo e na matéria. Os acoplamentos considerados entre os neutrinos e os bósons foram de tipo escalar ou pseudoescalar. Em particular estudamos os processos n i ® nj + c e n i ® n j + c (onde c representa o campo escalar ou pseudoescalar). No vácuo, calculamos as taxas efetivas na ordem mais baixa da teoria de perturbações usando o formalismo convencional para neutrinos de Majorana. Calculamos estas mesmas taxas para o caso da matéria usando o formalismo de helicidade de dois componentes introduzido em [P. Mannheim, Phys. Rev. D. 37, 1935 (1988)] para uma teoria geral (n, m), onde se tem n campos que pertencem a isodubletos de SUL(2) (neutrinos ativos) e m campos isosingletos de SUL(2) (neutrinos estéreis). Decaimentos de neutrinos com tempos de vida relativamentes longos podem ser provados, em principio, através de observações de neutrinos relíquias de supernovas. Portanto, calculamos o uxo de antineutrinos ne relíquias de supernovas que chegam à terra considerando simultaneamente as oscilações e os decaimentos dos neutrinos mencionados anteriormente
Abstract: In this work we study nonradiative decays of Majorona neutrinos, via massless bosons, in vacuum and matter. The considerate couplings between the neutrinos and the bosons were scalar and pseudoscalar. In particular we study the processes n i ® nj + c e n i ® n j + c (where is either scalar or pseudoscalar field). In vacuum, we calculate effective rates in the lowest order of the perturbation theory using the conventional formalism for Majorana neutrinos. We calculate the same rates in the matter case using the two-component helicity formalism introduced in [P. Mannheim, Phys. Rev. D. 37, 1935 (1988)] for a general theory, where there are neutrino fields belong to SUL(2) isodoublets (active neutrinos) and neutrino fields belong to SUL(2) isosinglets (sterile neutrinos). Neutrino decays of relatively long lifetimes could be proved, in principle, through of supernova relic neutrino (SRN) observations. Therefore, we calculate the antineutrinos ux of SRN that arrive to the Earth simultaneously considering both neutrino oscillations and the previously mentioned neutrino decays
Mestrado
Física das Particulas Elementares e Campos
Mestre em Física

Les supernovae de type la (SNe la) sont un des piliers de la cosmologie observationnelle moderne, celles-ci étant de bonnes chandelles standards utilisables pour des mesures de distances dans l'univers. L'analyse cosmologique à partir des SNe la s'appuie sur les mesures d'objets à grands et petits décalages vers le rouge (z), et actuellement le faible nombre d'observations de ces derniers constitue une source majeure d'incertitude. Cette thèse s'inscrit dans le cadre de l'expérience SNfactory, qui a pour objectif l'observation de SNe la proches (0. 03 < z < 0. 08) grâce à un spectrographe de champ intégral, SNIFS. Le travail présenté a porté d'une part sur l'étalonnage de la voie photométrique de SNIFS, et d'autre part sur l'analyse des courbes de lumière spectrophotométriques issues des données de SNIFS. Ces études ont abouties à la création du premier diagramme d'Hubble spectrophotométrique pour des SNe la proches. Une chaîne d'extraction de rapports photométriques entre nuits, nécessaires pour l'étalonnage en flux des spectres, a été mise en oeuvre. Les erreurs systématiques de ces rapports ont été estimées comme étant inférieures à 2%, et les courbes de lumière spectrophotométriques d'étoiles standards montrent une précision de 5% pour l'étalonnage absolu en flux dans des conditions non-photométriques. Les résidus du diagramme d'Hubble obtenu présentent une dispersion plus petite que celui fait avec les données disponibles à ce jour. Un ajustement cosmologique sans K-correction montre une réduction supplémentaire de 5%, qui jusqu'à présent était indistinguable de la "dispersion intrinsèque" des SNe la
Type la supernovae (SNe la) are one of the pillars of modem observational cosmology, since they are good standard candies for distance measurements in the universe. The cosmological analysis using SNe la requires the observation of both high and low-redshift objects, and the smaller statistic of events on the latter case represents a major source of uncertainties. This thesis takes place within the SNfactory project, which aims to study nearby (0. 03 < z < 0. 08) SNe la using an integral field spectrograph, SNIFS. The presented work is divided into: a technical part, dealing with the acquisition, calibration and extraction of data from the SNIFS photometric camera; and an analysis where spectrophotometric light curves issued frc-m SNIFS spectra were obtained, and used to create the first spectrophotometric nearby Hubble diagram. An extraction pipeline of the differential photometric ratios between nights, needed for the flux calibration of the spectra, was built. The systematic errors affecting these ratios are estimated to be below 2%, and spectrophotometric light curves of standard stars show a 5% photometric precision of the full flux calibration on non-photometric conditions. The obtained nearby Hubble diagram presents a smaller residual scatter than the one made using currently available data. A K-correction free cosmological fit shows an additional reduction of 5% on the scatter, until now undistinguishable from the SNe la "intrinsic dispersion"

L'explosion en supernova gravitationnelle représente le stade ultime de l'évolution des étoiles massives.La contraction du cœur de fer peut être suivie d'une gigantesque explosion qui donne naissance à une étoile à neutrons.La dynamique multi-dimensionnelle de la région interne, pendant les premières centaines de millisecondes, joue un rôle crucial sur le succès de l'explosion car des instabilités hydrodynamiques sont capables de briser la symétrie sphérique de l'effondrement.Les mouvements transverses et à grande échelle générés par deux instabilités, la convection induite par les neutrinos et l'instabilité du choc d'accrétion stationnaire (SASI),augmentent l'efficacité du chauffage de la matière par les neutrinos au point de déclencher une explosion asymétrique et d'impacter les conditions de naissance de l'étoile à neutrons. Dans cette thèse, les instabilités sont étudiées au moyen de simulations numériques de modèles simplifiés.Ces modèles permettent une vaste exploration de l'espace des paramètres et une meilleure compréhension physique des instabilités, généralement inaccessibles aux modèles réalistes.L'analyse du régime non-linéaire de SASI établit les conditions de formation d'un mode spiral et évalue sa capacité à redistribuer radialement le moment cinétique.L'effet de la rotation sur la dynamique du choc d'accrétion est également pris en compte.Si la rotation est suffisamment rapide, une instabilité de corotation se superpose à SASI et impacte grandement la dynamique.Les simulations permettent de mieux contraindre l'importance des modes non-axisymétriques dans le bilan de moment cinétique de l'effondrement du cœur de fer en étoile à neutrons.SASI pourrait sous certaines conditions accélérer ou ralentir la rotation du pulsar formé dans l'explosion.Enfin, une étude d'un modèle idéalisé de la région de chauffage est menée pour caractériser le déclenchement non-linéaire de la convection par des perturbations telles que celles produites par SASI ou les inhomogénéités de combustion pré-effondrement.L'analyse de la dimensionnalité sur le développement de la convection permet de discuter l'interprétation des modèles globaux et met en évidence les effets bénéfiques de la dynamique tridimensionnelle sur le déclenchement de l'explosion
A core-collapse supernova represents the ultimate stage of the evolution of massive stars.The iron core contraction may be followed by a gigantic explosion which gives birth to a neutron star.The multidimensional dynamics of the innermost region, during the first hundreds milliseconds, plays a decisive role on the explosion success because hydrodynamical instabilities are able to break the spherical symmetry of the collapse.Large scale transverse motions generated by two instabilities, the neutrino-driven convection and the Standing Accretion Shock Instability (SASI),increase the heating efficiency up to the point of launching an asymmetric explosion and influencing the birth properties of the neutron star.In this thesis, hydrodynamical instabilities are studied using numerical simulations of simplified models.These models enable a wide exploration of the parameter space and a better physical understanding of the instabilities, generally inaccessible to realistic models.The non-linear regime of SASI is analysed to characterize the conditions under which a spiral mode prevails and to assess its ability to redistribute angular momentum radially.The influence of rotation on the shock dynamics is also addressed.For fast enough rotation rates, a corotation instability overlaps with SASI and greatly impacts the dynamics.The simulations enable to better constrain the effect of non-axisymmetric modes on the angular momentum budget of the iron core collapsing into a neutron star.SASI may under specific conditions spin up or down the pulsar born during the explosion.Finally, an idealised model of the heating region is studied to characterize the non-linear onsetof convection by perturbations such as those produced by SASI or pre-collapse combustion inhomogeneities. The dimensionality issue is examined to stress the beneficial consequences of the three-dimensional dynamics on the onset of the explosion

The SuperNovae Analysis aPplication (SNAP) is a new tool for the analysis of SN observations and validation of SN models. SNAP consists of a publicly available relational database with observational light curve, theoretical light curve, and correlation table sets with statistical comparison software, and a web interface available to the community. The theoretical models are intended to span a gridded range of parameter space. The goal is to have users upload new SN models or new SN observations and run the comparison software to determine correlations via the website. There are problems looming on the horizon that SNAP is beginning to solve. For example, large surveys will discover thousands of SNe annually. Frequently, the parameter space of a new SN event is unbounded. SNAP will be a resource to constrain parameters and determine if an event needs follow-up without spending resources to create new light curve models from scratch. Second, there is no rapidly available, systematic way to determine degeneracies between parameters, or even what physics is needed to model a realistic SN. The correlations made within the SNAP system are beginning to solve these problems.

The progenitors of core-collapse supernovae are stars with an initial mass greater than about 8M⊙. Understanding the evolution of these stars is necessary to comprehend the evolution and differences between supernovae. We have constructed new and unique opacity tables to increase model accuracy during the latest stages of stellar evolution. We have investigated how initial mass, initial composition and mass loss affects the progenitors and their populations. There are many prescriptions for mass loss. Different research groups use their preferred rates. We have compared 12 different prescriptions and determined which provides the best fit to observations. We use our preferred mass-loss scheme to make suggestions as to the source of the differences between supernova types from our progenitor models. Binary evolution is considered in order to search for low luminosity SN progenitors and progenitor types not possible from single stars. Removal of the hydrogen envelope is more common and we find quite different hydrogen deficient SN progenitors. We discuss the implications of our binary models for ultra-luminous X-ray sources and gamma-ray bursts. We present an estimation of the mass distribution for black holes at various metallicities showing that massive black holes are not formed until very low metallicities. Finally we combine the single star and binary results to determine their relative populations and compare to observations. However it is not possible to draw many firm conclusions because of the uncertainty in observations to date.

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

Supernovae are important probes of cosmology. In 1999, Type Ia Supernovae (SNeIa) provided the first evidence for the accelerating expansion of the Universe (Riesset al., 1998, Perlmutter et al., 1999), and since then there have been many wide-field SN surveys with the scope of increasing the number of observed SNe, thus improving the constraints on cosmological parameters. Among these SN surveys,the Dark Energy Survey (DES) and the planned Large Synoptic Survey Telescope(LSST) will increase the number of available SNe Ia respectively to ' 3000 and ∼10⁵ (possibly ∼ 10⁶) in the coming decade. Weak gravitational lensing effects willthen become important for these new surveys. Weak gravitational lensing have different effects on the distance modulus measurements of SNe. Firstly, it introduces a non-Gaussian scatter on the distance moduli of SNe Ia, and this effect increases as a function of redshift. The non-Gaussian weak lensing distribution can also introduce a bias on the cosmological parameter values recovered by fitting the Hubble diagram. Secondly, it introduces spatial correlations on the magnitudes of close SN pairs, with angular separation of the order of arcminutes. Weak lensing of SNe can also be used to probe the growth of structures along the line-of-sight, giving further constraints on cosmological parameters like σ₈ and Ω_m. In Chapter 2, we present our results on the fit of the Hubble diagram from the Jointed Light-curve Analysis sample (JLA, Betoule et al. 2014) including weak lensing and peculiar velocities, the latter introducing an extra dispersion on the distance modulus measurements of low redshift SNe. We give constraints on the cosmological parameters when fitting for the the first four moments of the weak lensing distribution together with the variance induced by peculiar velocities. We test our method via numerical simulations and we find Ω_m=0.274±0.013 and σ₈=0.44^+0.63_-0.44 when fitting the JLA sample. We also apply the Kernel Density Estimation technique to reduce the problem of biased estimates of the moments measured on sparse data sample, and a boot-strap re-sampling method when computing the covariance between the moments. In Chapter 3 we propose to measure the two-point magnitude correlation function from SN data and compare such measurements to theoretical expectations. As available data sample appear to be insufficient to detect this weak correlation (we report a tentative detection with the JLA sample), we predict measurements with current (DES) and future (LSST) SN surveys, finding that the LSST should be able to detect such correlations at 6σ level of confidence (15,000 SNe over 70 deg² and assuming an intrinsic scatter of 0.15 magnitudes). DES (deep field) is expected to detect a cross-correlation between the Hubble residuals and the foreground galaxies at 12σ (integrated up to 9 arcminutes of separation and assuming an intrinsic scatter of 0.15 magnitudes), taking advantage of the higher galaxy density on the sky, while LSST should detect the same cross-correlation with signal-to-noise ⪆ 100. We also give forecasts on cosmological parameters when fitting Ωm and σ₈ from the twopoint magnitude auto-correlation function, i.e. we can achieve a 25% measurement of σ₈ from LSST (assuming 0.15 magnitudes of intrinsic scatter and applying a Gaussian prior on the matter density parameter). In Chapter 4, we investigate Type Ic Superluminous Supernovae (SLSNe Ic) as a new class of potential standard candles, which appear to be standardisable in their peak magnitudes with a scatter of only 0.2 – 0.3 magnitudes. Moreover, their exceptional peak magnitude (up to 100 times brighter than SNe Ia) allows them to be discovered to redshift ∼ 3, shedding new light on the deceleration epoch of the Universe. We give predictions for SLSN Ic redshift distribution within present (DES and SUDSS, which are expected to find 15 and 75 SLSNe respectively) and future surveys (LSST and Euclid, which should increase the available SLSNe to   10; 000 and 300 respectively, the latter up to redshift 4). We construct simulated Hubble diagrams for SLSNe Ic, spanning the likely values of intrinsic scatter for these sources ( 0:15 - 0:25 magnitudes), and fit the Hubble diagrams to infer cosmological constraints. We find that the addition of 75 SLSNe from SUDSS to the 3800 SNe Ia from DES can improve the constraints on w (the dark energy state parameter) and Ω_m by 20% (assuming a flat wCDM universe). Moreover, the combination of DES SNe Ia and 10,000 LSST SLSNe can measure Ω_m and w to 2% and 4% respectively. When considering temporal variations in w(a), we find possible uncertainties of 2%, 5% and 0.14 on Ω_m, w₀ and w_a respectively, from the combination of DES SNe Ia, LSST SLSNe and Planck Cosmic Microwave Background temperature power spectrum. We find that SLSNe from Euclid can constrain the matter density parameter to 10%, and can help constraining the equation-of-state parameters w₀ and w_a. All these surveys will also improve the knowledge about SLSN astrophysics, their progenitors and possible classification into sub-classes.

In future astronomical sky surveys it will be humanly impossible to classify the tens of thousands of candidate transients detected per night. This thesis explores the potential of using state-of-the-art machine learning algorithms to handle this burden more accurately and quickly than trained astronomers. To this end Deep Learning methods are applied to classify transients using real-world data from the Sloan Digital Sky Survey. Using cutting-edge training techniques several Convolutional Neural networks are trained and hyper-parameters tuned to outperform previous approaches and find that human labelling errors are the primary obstacle to further improvement. The tuning and optimisation of the deep models took in excess of 700 hours on a 4-Titan X GPU cluster.

The emission in the ultraviolet domain contains precious information about the supernova (SN) explosion: it is highly sensitive to the metallicity of the SN ejecta; it gives indications on the SN progenitor structure and on how it exploded; UV photons are produced during the interaction with the SN circumstellar material, revealing the environment structure and thus the precursor pre-explosion activity. For these reasons, the Thesis aims mainly to study the properties of SNe in the UV. In particular, it is focused on the analysis of new observations collected with Swift and GALEX satellites, which improve our current poor knowledge of the properties of the different SN Types in this wavelength range. Considering that the forthcoming high-redshift SN surveys will be conducted in the optical and IR ranges, which samples the UV rest-frame emission of the SN, the knowledge of the UV spectral evolution of the local SNe is essential to properly exploit the surveys outputs. Despite the wide interest, to date the sample of SN spectroscopically observed in the UV is still small. With this Thesis we remarkably increased the number of SNe observed in the UV. After a general overview on our current understanding of SNe and their UV emission, we will present for the first time the entire Swift archive of SN spectroscopic observations, obtained during the first two years of observations (2005--2006). The Swift sample includes 9 SNe, specifically 6 SNe Type Ia (SNe 2005am, 2005cf, 2005df, 2005ke, 2005hk and 2006X), 2 Type II (SNe 2005cs and 2006bp) and 1 Type Ib/c (SN 2006jc), collecting 31 UV-grism and 22 V-grism spectra. The limited S/N of the data has been improved by applying an optimized extraction technique and the offset in the zero point of the wavelength calibration removed through the comparison with quasi-simultaneous ground-based spectra. An important step toward the characterization of SNe in the Ultraviolet has been achieved with this work. Indeed, with SN 2005cf, we obtained the best UV spectral follow-up to date for a Type Ia SN, with 7 UV spectra collected during the pre-maximum phases, which improves the past exceptional performance of IUE. In general, the UV spectra of SNe Ia, though to originate predominantly from reverse fluorescence in iron group ions present in the ejecta outermost layers, are found to be characterized mainly by two broad absorptions at about 3050 A and 3250 A [due to Fe, Co, Cr and Ti lines, Kirshner92A, sauer08]. A comparison of the Swift SN Ia spectra with those in literature of SNe 1992A and 1990N shows that SNe Ia with similar optical properties may have different UV behaviour. SN 2006jc, the only Type Ib/c SN in our spectroscopic sample, shows two strong and broad UV emissions at ~2800-3000A, unusual at early epochs and that can be interpreted as a signature of the interaction between the SN ejecta and gas originally ejected by the stellar progenitor. The UV spectra of both Type IIP SNe 2005cs and 2006bp are found to be shaped by blends of singly ionized iron-peak elements lines (mostly FeII, NiII) and MgII, yielding a line blanketing effect, which increases with decreasing temperature. From the comparison of the first 2-years of \swift\ observations to the 15-year IUE activity on Sne, the large number of observations that Swift already collected stands out, as does its great flexibility and rapid reaction time that allow the prompt start of the observational campaigns after the SN discovery and its systematic follow-up. In the second part of the Thesis, the analysis will be focused on the very interesting SN 2005ay, a Type II SN in NGC 3938 of the Plateau subclass. SN 2005ay has been the first target observed within a wide observational program for the multiwavelength study of CC SNe. We will present and analyze the UV spectra of SN 2005ay taken with GALEX (at 4 spectroscopic epochs), as well as the huge amount of spectroscopic and photometric data (107 Optical + 19 NIR photometric epochs and 20 optical spectra) obtained in the Optical-NIR range with 11 different ground-based telescopes. Such extended wavelength sampling, together with the detailed time follow-up, makes SN 2005ay a SN with one of the best coverages ever (after only SN 1987A). For this reason SN 2005ay is going to become a "golden template", for Type II SNe, specifically for SN II-Plateau. With this Thesis, we give a great contribution to the enlargement SN Type II Plateau sample. In fact, despite SNe IIP represent the largest fraction of SN II, only two objects in literature had sufficient data to describe their evolution: SNe 1999em and 1987A. Considering the very peculiar behaviour of the latter, adding SNe 2005ay and 2005cs we actually triple the number of typical SNe IIP observed in the UV with good quality data. The comparative study of the SN IIP sample shows a remarkable similarity among these objects, which, if confirmed by additional SNe II-P, would indicate the cosmological use of II-P SNe as a promising prospect. Finally, as last contribution of this Thesis we will compare the spectral energy distributions (in the range 2000-10000 A) of the main SN Types, discussing the importance of the strong difference between the UV emissions of Type Ia and CC SNe for the possible future use of the photometry as a reliable instrument to classify SNe at very high redshifts.
Lo studio dell'emissione nella banda Ultravioletta di una Supernova permette di ottenere preziose informazioni circa l'evento stesso: essa e' molto sensibile alla metallicita' dell'ejecta della SN; fornisce indicazioni sulla struttura del progenitore e su come esso sia esploso; fotoni UV sono prodotti durante l'interazione con il materiale circumstellare presente attorno alla SN, rivelando la struttura dell'ambiente circostante e quindi le fasi evolutive del progenitore precedenti all'esplosione. Per queste ragioni, la Tesi e' principalmente indirizzata allo studio delle proprieta' UV delle SNe. In particolare, essa e' focalizzata sull'analisi delle nuove osservazioni ottenute con i satelliti Swift e GALEX, migliorando l'attuale scarsa conoscenza delle proprieta' dei diversi tipi di SNe in questo specifico intervallo di lunghezze d'onda. Considerando che le imminenti surveys di SNe ad alto redshift saranno condotte utilizzando le bande ottiche e infrarosse, che campionano in realta' l'emissione UV della SN nel suo sistema a riposo, la comprensione dell'evoluzione spettrale nell'UV delle SN locali e' essenziale per interpretare correttamente i risultati delle stesse surveys. Nonostante l'ampio interesse, tutt'oggi il campione di SNe osservate spettroscopicamente nell'UV e' ancora molto ristretto. Dopo una panoramica generale sulla comprensione attuale del fenomeno SN e delle loro emissioni nell'UV, presenteremo per la prima volta l'intero dataset di osservazioni spettroscopiche di SNe, ottenuto con Swift duranti i primi due anni di attivita' (2005-2006). Il campione di SNe conta 9 oggetti, di cui 6 SNe Tipo Ia (SNe 2005am, 2005cf, 2005df, 2005ke, 2005hk e 2006X), 2 Tipo II (SNe 2005cs e 2006bp) e 1 Tipo Ib/c (SN 2006jc), per un totale di 31 spettri ottenuti con il grism UV e 22 con quello V. Il basso rapporto segnale-rumore che caratterizza i dati e' stato migliorato grazie all'applicazione di una tecnica di estrazione ottimizzata e il problema dello spostamento del punto zero della calibrazione in lunghezza d'onda risolto con il confronto con gli spettri quasi-simultanei ottenuti da telescopi terrestri. Un importante passo verso la caratterizzazione delle SNe nell'UV e' stato compiuto con questo lavoro. Infatti, con SN 2005cf, presentiamo il miglior follow-up UV finora ottenuto per una SN Ia, con 7 spettri UV presi durante le fasi precedenti al massimo, migliorando la precedente gia' eccezionale performance di IUE. In generale, gli spettri UV delle SNe Ia, formati principalmente dal processo di reverse fluorescence negli ioni dei metalli presenti negli strati piu' esterni dell'ejecta, presentano principalmente due assorbimenti larghi a circa 3050 A e 3250 A [dovuti alle righe del Fe, Co, Cr e Ti, Kirshner92A, sauer08]. Un confronto fra gli spettri Swift di SNe Ia e quelli presenti in letteratura delle SNe 1992A e 1990N mostra che le SNe Ia con propriet\`a simili nell'ottico possono differire nell'UV. SN 2006jc, l'unica SN Ib/c del nostro campione spettroscopico, presenta due forti emissioni, rare nelle fasi iniziali, a ~2800-3000 A, che possono essere interpretate come il segno dell'interazione fra l'ejecta della SN e il gas originariamente espulso dalla stella progenitrice. Gli spettri UV di entrambe le SNe IIP, SN 2005cs e SN 2006bp, sono modellati dal "blend" delle righe dei metalli ionizzati (come FeII e NiII) e del MgII, producendo un effetto di "line blanketing" che aumenta con l'abbassarsi della temperatura. Dal confronto delle osservazioni di SNe ottenute con Swift durante i suoi primi due anni e quelle dei 15 anni di attivita' di IUE, l'elevato numero di spettri UV gia' ottenuto con Swift si evidenzia, come anche la sua grande flessibilita' e il suo rapido tempo di risposta che permettono l'avvio della campagna osservativa immediatamente dopo la scoperta ed un'elevata frequenza di osservazioni dello stesso target. Nella seconda parte della Tesi, l'analisi e' focalizzata sull'interessante SN 2005ay, una SN Tipo II esplosa in NGC 3938, appartenente alla sottoclasse delle II Plateau. SN 2005ay e' stato il primo target osservato all'interno di un vasto progetto di osservazione di CC SNe in un ampio intervallo spettrale. Presenteremo e analizzeremo gli spettri UV di SN 2005ay ottenuti con GALEX (a 4 epoche spettroscopiche), insieme all'enorme dataset spettroscopico e fotometrico (126 notti di fotometria e 20 spettri ottici) collezionato nell'ottico e vicino infrarosso presso 11 diversi telescopi. L'estensione in lunghezza d'onda del campionamento e il dettagliato follow-up temporale fa di SN 2005ay una delle SNe con la miglior copertura mai ottenuta (seconda solo a SN 1987A). Per questa ragione, SN 2005ay diventera' un "golden template" per le SNe di Tipo II, specialmente per le Tipo IIP.\\ Con questa Tesi, abbiamo contribuito all'aumento del campione di SNe IIP osservate nell'UV. Infatti, nonostante rappresentino la frazione maggiore di SN Tipo II, solemente due sono gli oggetti in letteratura osservati nell'UV: SN 1999em e SN 1987A. Considerando la peculiarita' di quest'ultima, in pratica aggiungendo SNe 2005ay e 2005cs al campione abbiamo triplicato il numero di SN IIP tipiche con dati UV di buona qualita'. Lo studio comparativo delle SNe IIP nell'UV ha rivelato una notevole somiglianza fra gli oggetti di questa classe, che, se confermata dall'osservazione futura di ulteriori SN IIP, potrebbe confermare l'attendibilita' di queste SNe come indicatori di distanza. In conclusione, come contributo finale di questa Tesi, abbiamo confrontato la distribuzione spettrale di energia (nell'intervallo 2000-10,000 A) dei principali tipi di SNe, discutendo l'importanza che la grande differenza di emissione nell'UV fra SNe Ia e CC puo' avere nel futuro possibile uso della sola fotometria come strumento attendibile per la classifizione delle SNe a redshift molto alti.

Cette thèse se propose d'étudier plusieurs phénomènes hydrodynamiques et magnétohydrodynamiques pouvant induire une asymétrie dans les explosions de supernovae gravitationnelles. Dans la première partie de ce manuscrit consacrée au contexte général, nous décrivons d'abord les indications théoriques et observationnelles suggérant une asymétrie importante. Nous présentons ensuite plusieurs instabilités susceptibles de briser la symétrie sphérique initiale, en insistant en particulier sur le rôle de l'instabilité du choc d'accrétion nommée SÀSI. La deuxième partie constitue une étude hydrodynamique de SASI. Nous présentons tout d'abord un argument utilisant la fréquence des modes instables et permettant de trancher entre les deux mécanismes proposés pour expliquer la croissance linéaire de SASI. Dans un deuxième temps, nous étudions la dynamique non linéaire de SASI et proposons pour la première fois un mécanisme responsable de sa saturation. Dans ce scénario, la saturation est due à la croissance d'instabilités parasites sur le mode de SASI. La prédiction semi analytique de l'amplitude de saturation est comparée avec succès à des simulations numériques publiées. La troisième partie décrit l'effet d'un champ magnétique modéré. Nous montrons que celui-ci peut avoir un effet stabilisant ou déstabilisant sur SASI selon sa géométrie. Nous nous concentrons ensuite sur la dynamique d'une surface d'Alfvén, où les vitesses d'advection et d'Alfvén coïncident. Nous montrons que l'amplification d'ondes d'Alfvén à proximité de cette surface crée une rétroaction acoustique, qui pourrait affecter la dynamique du choc si l'énergie magnétique est comparable à l'énergie cinétique
This thesis is devoted to the study of several hydrodynamical and magnetrohydrodynamical phenomena that could create an asymmetry in core collapse supernovae. In the first part giving the general context, we first describe the theoretical and observational indications suggesting an I important asymmetry. We then present several instabilities that could break the initial spherical symmetry, insisting particularly on the role of the Stationary Accretion Shock Instability (SASI). The second part is dedicated to a hydrodynamical study of the Standing Accretion shock instability. We first give an argument using the frequency of unstable modes that enables us to distinguish between the two mechanisms proposed to explain the linear growth of SASI. As a second step, we study thé non-linear dynamics of SASI and propose for the first time a mechanism responsible for its saturation. In this scenario, the saturation occurs when parasitic instabilities are able to grow fast enough on a SASI mode. The semi-analytical prediction of the saturation amplitude is successfully compared with published numerical simulations. The third part studies the effect of a moderate magnetic field. We find that such a magnetic field can have either a stabilizing or a destabilizing effect on SASI depending on its geometry. We then concentrate on the dynamics of the Alfvén surface, where the Alfvén and the advection speed coincide. We show that the amplification of Alfvén waves near this surface creates a pressure feedback, which could affect significantly the dynamics of the shock if the magnetic energy is comparable to the kinetic energy

Vers la fin des années 1990, l'utilisation des supernovae de type Ia (SNe Ia) comme indicateurs de distance a permis de mettre en évidence l'expansion accélérée de l'univers. Depuis lors, des campagnes d'observations de grandes envergures ont permis d'augmenter de façon significative le nombre de SNe Ia observées, mais les incertitudes systématiques liées à la qualité des échantillons de SNe Ia proches restent un facteur limitant sur la précision des mesures actuelles. C'est dans le but de réduire ces incertitudes que le projet the Nearby Supernova Factory (SNfactory), à l'aide d'un instrument spectro-photométrique dédié à l'observation des SNe Ia (the Supernova Integral Field Spectrograph), a collecté depuis 2004 plus de 3000 spectres de près de 200 SNe Ia proches. Une des limitations actuelles de leur utilisation, outre les aspects liés aux problèmes d'inter-calibration entre les différentes expériences, est celle du mélange des différentes composantes de leurs variabilités lors de la standardisation empirique de leur module de distance. Une meilleure séparation de ces composantes, ainsi que la découverte de nouveaux indicateurs de distance, font partie des améliorations que peut apporter un échantillon spectral de SNe Ia proches tel que celui de la collaboration SNfactory. Cette thèse de doctorat, effectuée à l'Institut de Physique Nucléaire de Lyon et au Lawrence Berkeley National Laboratory, s'inscrit directement dans cette problématique, en se concentrant sur la mesure d'indicateurs spectraux sur l'échantillon spectral de la collaboration Snfactory. Le plan de cette thèse est le suivant : La première partie présente le contexte scientifique ainsi que l'échantillon de SNe Ia de la collaboration SNfactory utilisé dans les analyses. La deuxième partie se concentre sur la méthode de mesure d'indicateurs spectraux appliquée à l'échantillon spectrale présenté, ainsi que sur une étude de leur sensibilité à l'extinction par le milieu interstellaire. La troisième partie est une étude des corrélations des indicateurs spectraux et de leur utilisation pour la standardisation des Sne Ia. Dans la dernière partie, une utilisation de ces indicateurs spectraux pour la détermination d'une loi d'extinction moyenne est présentée

Dans cette thèse, effectuée en cotutelle avec l'Université d'Oklahoma City, nous avons étudié le transfert radiatif dans les enveloppes en expansion rapide des supernovae de type Ia (SNeIa) dans le cadre de la collaboration SupernovaeFactory. Ces étoiles qui explosent avec une luminositée comparable à celle d'une galaxie sont utilisées comme chandelles standard permettant d'étudier le comportement à grande échelle de l'univers. Nous avons utilisé le code de transfert radiatif PHOENIX développé par P. Hauschildt, F. Allard et E. Baron, pour simuler des spectres de SNeIa à différentes dates et luminosités afin d'étudier le processus de formation spectrale. Nous avons parallèlement élaboré un module de grille adaptative qui augmente sa robustesse de convergence. Nous avons montré que la formation des spectres de SNeIa n'était pas aussi localisée que dans le modèle photospherique standard mais qu'elle mettait en relation des régions allant de 5000 km/s à 20000 km/s pour des époques proches du maximum de luminosité. Nous avons de plus développé des indicateurs spectraux permettant de mesurer la luminosité des SNeIa avec une précision égale à celle des méthodes basées sur l'analyse des courbes de lumière. Il devient ainsi possible de contraindre de façon indépendante l'évolution des SNeIa avec le redshift, ce qui place ce travail à l'interface entre l'étude des supernovae en tant qu'objets stellaires et leur utilisation en cosmologie

Les supernovae de type Ia (SNe Ia) sont de puissants indicateurs de distance cosmologique. Elles sont à l'origine de la découverte de l'énergie noire dans l'univers et restent aujourd'hui la meilleure méthode pour contraindre son équation d'état. Cependant, nous ignorons toujours le phénomène exact donnant naissance à ces supernovae. Notamment, nous ne connaissons pas l'influence de l'évolution des paramètres stellaires avec le redshift sur la luminosité de ces objets et donc sur les ajustements cosmologiques. De récentes études ont mis en évidence évidence des biais environnementaux ayant un impact significatif sur les mesures des paramètres cosmologiques. Cependant, ces études analysent les hôtes des SNe Ia dans leur globalité en négligeant les variations pourtant connues des propriétés stellaires et gazeuses au sein de ces galaxies. ! Dans cette thèse je montre comment les données de spectrographie à champ intégral de la collaboration The Nearby Supernova Factory permettent l'étude de l'environnement immédiat (~kpc) de la SNe Ia. Dans une première partie, j'introduis les bases physiques et le contexte scientifique dans lesquels ma thèse s'inscrit. Dans la seconde partie, je commence par détailler les techniques d'extraction des données environnementales locales et, une fois ces données extraites, je développe la mesure du taux de formation stellaire environnant les SNe Ia à partir du signal Hα. Dans mon analyse, je montre comment les propriétés des SNe Ia, et notamment leur luminosité standardisée, dépendent de la présence de formation stellaire à proximité. Ce biais, duquel découlent les biais environnementaux précédemment évoqués, a un impact significatif sur la cosmologie. En se basant sur les évolutions des propriétés stellaires des galaxies, je construit un modèle d'évolution de la luminosité moyenne des SNe Ia en fonction du redshift pour estimer cet impact; les données de la littérature semblent confirmer mes hypothèses. Ces résultats ont été publiés dans le journal européen Astronomy & Astrophysics (Rigault et al. 2013). Dans une troisième partie, je présente des analyses supplémentaires sur l'environnement local des SNe Ia et je suggère de nouvelles approches. ! Cette thèse a mis en évidence un biais environnemental important sur les propriétés des SNe Ia que seule l'analyse locale permet d'aborder. Cette découverte est une étape importante dans la compréhension de ces objets et dans l'amélioration de leur utilisation cosmologique
Type Ia supernovae (SNe Ia) are powerful cosmological distance indicators. They were key tools for the discovery of the accelerating expansion of the Universe and today they remain the strongest demonstrated technique for measuring the dark-energy equation of state. However, a major issue remains: despite decades of study, their progenitors are as yet undetermined. Notably, we still ignore the influence of the redshift-evolution of stellar properties on the absolute luminosity of the SNe Ia and therefore on the fitted cosmological parameters. Recent studies have highlighted potential biases correlated with the global properties of their host galaxies, large enough to induce systematic errors into cosmological measurements if not properly treated. However, those studies analyse hosts of Type Ia supernovae globally thus neglecting the known stellar and gas property variations across galaxies. ! In this thesis, I show how integral field spectroscopy data from the Nearby Supernova Factory allow the study of the local environment of the SNe Ia (~kpc). In the first part of this document, I introduce the physical principals and the scientific context of this work. In a second part, I start by detailing the technical extraction tools developed in order to extract the local host properties. Then, I show how one could measure the star formation activity in the SN vicinity from those data. I focus the analysis on this star formation activity and notably I show how the SNe Ia properties -- particularly their standardised Hubble residuals -- depend on the local host environment, which corresponds to a significant cosmological bias. I finish this second part by introducing a simple model based on the known evolution of the galactic star formation activity. This model enables me to estimate the potential influence of the aforementioned environmental bias on cosmology. I also show that this model can be tested using public data and a first analyses tend to confirm our hypotheses. Those results have been published in Astronomy & Astrophysics (Rigault et al. 2013). The third and last part of the document introduces new approaches and future work perspectives. ! In this thesis, I have highlighted significant environmental biases in SNe Ia properties, thanks to the local approach. However, those biases are less an issue for the cosmological analyses using Type Ia supernovae than a new opportunity to improve them as cosmological probes. ! This Document is written in French. The figures are in English

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.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Submitted.

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.

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.

Using two techniques not previously applied to Cassiopeia A (Cas A), we measure the reddening toward its expansion center. An estimate of AV from the near-IR [Fe II] lines is hampered by uncertain atomic data, though the spatial variation in their flux ratio allows relative measurement of the extinction in regions without previous optical estimates. We use a second technique based on the broad-band IR shape of the synchrotron emission, and find Aᵥ = 6.2 ± 0.6 for a knot 13" from the expansion center. Assuming a plausible lower limit on the apparent magnitude of the SN in outburst, the ⁵⁶Ni yield was 0.058 < M(Ni) < 0.16M⊙. With the ⁴⁴Ti mass from published gamma-ray observations, this implies a ⁴⁴Ca/ ⁵⁶Fe ratio consistent with the solar abundance. Recently published Spitzer Space Telescope IRS observations detect dust and line emission from cold gas interior to Cas A’s reverse shock. Using simple physical arguments and new hydrodynamic, non-equilibrium photoionization calculations, we infer the physical conditions in this material. We find that the mid-IR bright clumps are photoionized by the SNR shocks, over-dense relative to the expected average in the interior of the remnant, and have abundances consistent with incomplete oxygen burning. The lack of detectable iron lines indicates that any Si-burning material still interior to the reverse shock must be far more tenuous than the clumps of O-burning ashes. Finally, we present calculations from a new multi-dimensional hydrodynamics and non-equilibrium ionization and cooling code designed to model the emission from SNR shocks. Two-dimensional simulations of a shock-cloud interaction in a pure-oxygen plasma, with flow parameters relevant to Cas A, show a wider range of temperatures and ionization states than is typical in single-zone or 1D calculations, indicating that fluid and cooling instabilities play a role in producing the observed spectra of radiative shocks in metal-rich gas.

The use of type Ia supernovae as distance estimators has shown that about 75% of the energy content of the universe has a negative equation of state parameter and thus, drives the acceleration of the universe. Constraining the exact nature of this energy is one of the main goals in cosmology. As the statistics of observed high-redshift supernovae increases, systematic effects become the limiting factor to pursue such investigations, thus deeper understanding of the physical properties of SNe is of great importance.

In this thesis we investigate spectral homogeneity and diversity of local and high redshift supernovae. Special emphasis has been given to the analysis of optical spectra of local peculiar supernovae 1999aa and 1999ac. The study of the spectra of SN 1999aa pointed out that this SN could be a link between the extreme peculiar SN 1991T and normal SNe. Moreover, the identification of a high velocity component of Ca II and possibly of a low velocity component of C III suggests some degree of asphericity in the ejecta of this supernova. Evidence for a deflagration of a C+O white dwarf was found in the early spectra of SN 1999ac.

The spectral proprieties of a vast sample of local SNe are also studied by means of newly introduced spectral indicators. These were used to possibly improve the intrinsic spread of SN peak magnitudes to 0.15 mag, independently of light curve parameters.

The first quantitative comparison between local and high redshift supernova is carried out. No evidence for extreme peculiar sub-luminous SNe was found in our data set including 13 SNe with redshift range z=0.279-0.912. Furthermore, SN2002fd (z=0.279) was found to show spectral characteristics similar to SN 1991T/SN 1999aa-like supernovae.

We also present a feasibility study of the Hubble diagram in rest frame I-band up to z~0.5, and show the possibility to probe the presence of intergalactic dust, which could possibly mimic the effect of dark energy in the Hubble diagram.

Massive stars live fast and die young. They shine furiously for a few million years, during which time they synthesize most of the heavy elements in the universe in their cores. They end by blowing themselves up in a powerful explosion known as a supernova (SN). During this process, the core collapses to a neutron star or a black hole, while the outer layers are expelled with velocities of thousands of kilometers per second. The resulting fireworks often outshine the entire host galaxy for many weeks. The explosion energy is eventually radiated away, but powering of the newborn nebula continues by radioactive isotopes synthesized in the explosion. The ejecta are now quite transparent, and we can see the material produced in the deep interiors of the star. To interpret the observations, detailed spectral modeling is needed. This thesis aims to develop and apply state-of-the-art computational tools for interpreting and modeling SN observations in the nebular phase. This requires calculation of the physical conditions throughout the nebula, including non-thermal processes from the radioactivity, thermal and statistical equilibrium, as well as radiative transport. The inclusion of multiline radiative transfer, which we compute with a Monte Carlo technique, represents one of the major advancements presented in this thesis. On February 23 1987, the first SN observable by the naked eye since 1604 exploded, SN 1987A. Its proximity has allowed unprecedented observations, which in turn have lead to significant advancements in our understanding of SN explosions. As a first application of our model, we analyze the 44Tipowered phase (t & 5 years) of SN 1987A. We find that a magnetic field is present in the nebula, trapping the positrons that provide the energy input, and resulting in strong iron lines in the spectrum. We determine the 44Ti mass to 1.5(+0.5−0.5)*10−4 M⊙. From the near-infrared spectrum at an age of 19 years, we identify strong emission lines from explosively synthesized metals such as silicon, calcium, and iron. We use integral-field spectroscopy to construct three-dimensional maps of the ejecta, showing a morphology suggesting an asymmetric explosion. The model is then applied to the close-by and well-observed Type IIP SN 2004et, analyzing its ultraviolet to mid-infrared evolution. Based on its Mg I] 4571 Å, Na I 5890, 5896 Å, [O I] 6300, 6364 Å, and [Ne II] 12.81 mm nebular emission lines, we determine its progenitor mass to be around 15 M⊙. We confirm that silicate dust, SiO, and CO have formed in the ejecta. Finally, the major optical emission lines in a sample of Type IIP SNe areanalyzed.We find that most spectral regions in Type IIP SNe are dominated by emission from the massive hydrogen envelope, which explains the relatively small variation seen in the sample. We also show that the similar line profiles seen from all elements suggest extensive mixing occurring in most hydrogenrich SNe.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Accepted.