Neste trabalho investigamos os efeitos de choques (induzidos por supernovas) e de turbulência magneto-hidrodinâmica no processo de formação estelar. Primeiramente, considerando o impacto de um remanescente de supernova (RSN) com uma nuvem neutra magnetizada derivamos analiticamente um conjunto de condições através das quais estas interações podem levar à formação de estruturas densas capazes de tornarem-se gravitacionalmente instáveis e formar estrelas. Usando estas condições, construímos diagramas do raio do RSN, $R_$, versus a densidade inicial da nuvem, $n_c$, os quais delimitam um domínio no espaço paramétrico onde a formação estelar é permitida. Estes diagramas foram testados através de simulações numéricas magneto-hidrodinâmicas tridimensionais (3D MHD) onde seguimos a evolução espaço-temporal da interação de um RSN com uma nuvem auto-gravitante. Verificamos que a análise numérica está de acordo com os resultados previstos pelos diagramas. Observamos ainda que a presença de um campo magnético fraco, $\\sim 1 \\; \\mu$G, inicialmente homogêneo e perpendicular à velocidade de impacto do RSN, resulta em uma pequena diminuição da região permitida para formação estelar nos diagramas quando comparado a diagramas para nuvens não magnetizadas. Já um campo magnético mais intenso ($\\sim 10\\;\\mu$G) causa um encolhimento significativo nestas, como esperado. Embora derivados de considerações analíticas simples estes diagramas fornecem uma ferramenta útil para identificar locais onde a formação estelar pode ter sido induzida pelo impacto de uma onda de choque de SN. Aplicações a algumas regiões de nossa Galáxia (como a Grande Concha de CO na direção de Escorpião e a Nuvem Periférica 2 na direção da constelação de Cassiopeia) mostram que a formação estelar nestes locais pode ter sido induzida por uma onda de choque de um RSN em passado recente, quando se consideram valores específicos para as condições iniciais das nuvens impactadas.%, para valores específicos de raio do RSN e uma faixa de densidades iniciais possíveis para estas nuvens. Avaliamos também a eficiência de formação estelar efetiva para estas interações e encontramos que esta é geralmente menor do que os valores observados para a nossa Galáxia (sfe $\\sim$ 0.01$-$0.3). Este resultado é consistente com outros trabalhos da literatura e também sugere que este mecanismo, embora poderoso para induzir a formação de estruturas, turbulência supersônica e eventualmente formação estelar local, não parece ser suficiente para induzir a formação estelar global em galáxia normais, nem mesmo quando o campo magnético é desprezado. Além do estudo acima, exploramos ainda a formação estelar considerando a injeção prévia de turbulência (por um mecanismo físico arbitrário) em nuvens magnetizadas. Para uma nuvem ou glóbulo de nuvem molecular formar estrelas deve haver transporte de fluxo magnético das regiões internas mais densas para as regiões externas menos densas da nuvem, de outra forma o colapso poderá ser impedido pela força magnética. Consideramos aqui um novo mecanismo. Reconexão magnética rápida, a qual ocorre em presença de turbulência, pode induzir um processo de difusão eficiente dos campos magnéticos. Neste trabalho investigamos esse processo por meio de simulações numéricas 3D MHD e suas implicações para a formação estelar, estendendo um estudo prévio realizado para nuvens de simetria cilíndrica e sem auto-gravidade (Santos-Lima et al. 2010). Aqui consideramos nuvens mais realistas com potenciais gravitacionais esféricos (devido a estrelas embebidas) e também levando em conta os efeitos da auto-gravidade do gás. Determinamos, pela primeira vez, quais as condições em que o transporte do campo magnético devido à difusão por reconexão turbulenta leva uma nuvem inicialmente subcrítica a tornar-se super-crítica e capaz de colapsar para formar estrelas. Nossos resultados indicam que a formação de um núcleo supercrítico é resultado de uma complexa interação entre gravidade, auto-gravidade, intensidade do campo magnético e turbulência aproximadamente trans-sônica e trans-Alfvénica. Em particular, a auto-gravidade favorece a difusão do campo magnético por reconexão turbulenta e, como resultado, seu desacoplamento do gás colapsante torna-se mais eficiente do que quando apenas um campo gravitacional externo está presente. Demonstramos que a difusão por reconexão turbulenta é capaz de remover fluxo magnético da maior parte das nuvens investigadas, porém somente uma minoria desenvolve núcleos aproximadamente críticos ou super-críticos, o que é consistente com as observações. A formação destes é restrita ao seguinte intervalo de condições iniciais para as nuvens: razão pressão térmica-pressão magnética, $\\beta \\sim 1$ a $3$, razões entre a energia turbulenta e a energia magnética $E_/E_\\sim 1.62$ a $2.96$, e densidades $50 < n < 140$ cm$^$, quando consideramos massas estelares M$_{\\star}\\sim 25$M$_{\\odot}$, implicando uma massa total da nuvem (gás + estrelas) M$_\\lesssim 120$M$_{\\odot}$. / In this work, we have investigated the effects of shocks (induced by supernovae) and magnetohydrodynamical turbulence in the process of star formation. Considering first, the impact of a supernova remnant (SNR) with a neutral magnetized cloud we derived analytically a set of conditions through which these interactions can lead to the formation of dense structures able to become gravitationally unstable and form stars. Using these conditions, we have built diagrams of the SNR radius, $R_{SNR}$, versus the initial cloud density, $n_c$, that constrain a domain in the parameter space where star formation is allowed. These diagrams have been also tested by means of three-dimensional magneto-hydrodynamical (3D MHD) numerical simulations where the space-time evolution of a SNR interacting with a self-gravitating cloud is followed. We find that the numerical analysis is in agreement with the results predicted by the diagrams. We have also found that the effects of a weak homogeneous magnetic field ($\\sim 1 \\; \\mu$G) approximately perpendicular to the impact velocity of the SNR results only a small decrease of the allowed zone for star formation in the diagrams when compared with the diagrams with non-magnetized clouds. A larger magnetic field ($\\sim 10\\;\\mu$G) on the other hand, causes a significant shrinking of the star formation zone, as one should expect. Although derived from simple analytical considerations, these diagrams provide a useful tool for identifying sites where star formation could be triggered by the impact of a SN blast wave. Applications of them to a few regions of our own Galaxy (e.g., the large CO shell in the direction of Scorpious, and the Edge Cloud 2 in the direction of the Cassiopeia constellation) have revealed that star formation in those sites could have been triggered by shock waves from SNRs in a recent past, when considering specific values of the SNR radius and the initial conditions in the neutral clouds. We have also evaluated the effective star formation efficiency for this sort of interaction and found that it is generally smaller than the observed values in our Galaxy (sfe $\\sim$ 0.01$-$0.3). This result is consistent with previous work in the literature and also suggests that the mechanism presently investigated, though very powerful to drive structure formation, supersonic turbulence and eventually, local star formation, does not seem to be sufficient to drive $global$ star formation in normal star forming galaxies, not even when the magnetic field is neglected. Besides the study above, we have also explored star formation considering a priori injection of turbulence (by an arbitrary physical mechanism) in magnetized clouds. For a molecular cloud clump to form stars some transport of magnetic flux may be required from the denser, inner regions to the outer regions of the cloud, otherwise this can prevent the gravitational collapse. We have considered here a new mechanism. Fast magnetic reconnection which takes place in the presence of turbulence can induce a process of reconnection diffusion of the magnetic field. In this work, we have investigated this process by means of 3D MHD numerical simulations considering its implications on star formation. We have extended a previous study which considered clouds with cylindrical geometry and no self-gravity (Santos-Lima et al. 2010). Here, we considered more realistic clouds with spherical gravitational potentials (from embedded stars) and also accounted for the effects of the gas self-gravity. We demonstrated that reconnection diffusion takes place. We have also, for the first time, determined the conditions under which reconnection diffusion is efficient enough to make an initially subcritical cloud clump to become supercritical and collapse. Our results indicate that the formation of a supercritical core is regulated by a complex interplay between gravity, self-gravity, magnetic field strength and nearly transonic and trans-Alfvénic turbulence. In particular, self-gravity helps reconnection diffusion and, as a result, the magnetic field decoupling from the collapsing gas becomes more efficient than in the case when only an external gravitational field is present. We have demonstrated that reconnection diffusion is able to remove magnetic flux from most of the collapsing clumps analysed, but only a few of them develop nearly critical or supercritical cores, which is consistent with the observations. Their formation is restricted to a range of initial conditions for the clouds as follows: thermal to magnetic pressure ratios $\\beta \\sim$ 1 to 3, turbulent to magnetic energy ratios $E_{turb}/E_{mag}\\sim 1.62$ to $2.96$, and densities $50 < n < 140$ cm$^{-3}$, when considering stellar masses M$_{\\star}\\sim 25$M$_{\\odot}$, implying total (gas+stellar) masses M$_{tot} \\lesssim 120$M$_{\\odot}$.

Neste trabalho, faremos uma revisão bibliográfica com o objetivo de estudar e compreender algumas das informações que os neutrinos provenientes de Supernovas fornecem. Tais partículas são peças fundamentais para o entendimento do cenário catastrófico e turbulento presente neste fenômeno gigantesco de explosão. Para atingir tais objetivos, é fundamental estudar as características, os tipos e a dinâmica de explosão de Supernovas. Assim, com o conhecimento sobre oscilação de neutrinos, seremos capazes de identificar o papel que os neutrinos de Supernova desempenham na reconstrução dos seus respectivos fluxos. / In this work, we shall make a literature review in order to study and understand some of the information that neutrinos from supernovae provide. Such particles are fundamental to understand the catastrophic and turbulent scenario present in this gigantic explosion phenomenon. To achieve these goals, it is essential to study the characteristics, types and dynamics of exploding supernovas. Thus, along with the knowledge of neutrino oscillation, we will be able to identify the role that supernova neutrinos can play in the reconstruction of their fluxes.

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

The constant flux of cosmic rays that bombard Earth from within our own galaxy are understood to come from both shell-type supernova remnants and pulsar wind nebulae (PWNe). Multiwavelength study of these objects can help us to understand what types of particles are accelerated, and gamma-ray emission is key to understanding the highest energy cosmic rays. In this thesis, I analyze and interpret observations made with the Very Energetic Radiation Imaging Telescope Array System (VERITAS), a gamma-ray telescope located in Southern Arizona. LS 5039 and HESS J1825-137 occupy the same field of view on the sky and were observed for about 8 hours with VERITAS. LS 5039 is a gamma-ray binary, and the observations supports theories that the compact object hosts a PWN which is continuously interacting with the nearby star. HESS J1825-137 is a very extended PWN with an extent of diameter greater than 1 degree on the sky. Using the VERITAS observations, I am able to measure the radial profile and compare the gamma-ray luminosity to other PWN. DA 495, a "Crab-like" PWN with unusually strong magnetic fields, was observed for about 70 hours with VERITAS. In this study, results are combined with radio and X-ray spectral information to allow for detailed astrophysical modeling of the region. This broadband spectral modeling places constraints on the properties of the particle population in this PWN and allows for both leptonic and hadronic emission scenarios to be evaluated. Hadronic scenarios instil doubt on the pure PWN interpretation and favor a previously undetected shell-type remnant being present.

The main topic of this thesis is analysis of an unidentified Galactic TeV gamma-ray source, MGRO J1908+06, discovered by Milagro instrument in 2007. We analyzed 54 hours of observational data from the Very Energetic Radiation Imaging Telescope Array System (VERITAS), a ground-based gamma-ray observatory in southern Arizona comprised of an array of four Cherenkov Telescopes that reconstructs the energy and direction of astrophysical gamma-rays by imaging Cherenkov light emitted by energetic particles in air showers produced by the primary gamma-rays. MGRO J1908+06 is located between a supernova remnant SNR G40.5-0.5 and a young, energetic pulsar PSR J1907+0602. We studied the energy dependent morphology of the TeV emission from the source and measured the source extent and spectrum. The source extends well past the boundary of the SNR and is not correlated with strong radio continuum or molecular line emission which likely excludes an origin for the emission as solely due to the SNR. While emission in the 0.5-1.25 TeV band was centered around the pulsar, higher energy emission was observed near the supernova remnant. This morphology is opposite that observed in other pulsar wind nebulae. We proposed two models for the high energy emission located well away from the pulsar but close to the SNR: (1) shock acceleration at the shock front created by an interaction between the pulsar wind and the dense gas at the edge of the SNR or (2) molecular clouds around the SNR provides seed photons with energies higher than those from Cosmic Microwave Backgrounds for inverse Compton scattering. The former model can be tested by looking for molecular emission lines that trace shocks and by measuring the pulsar velocity. In addition, we investigated the gamma-ray emission from the nova explosion of V407 Cygni that occurred in March 2010. The Fermi-LAT observed this event in the energy range of E >100 MeV. The origins of the gamma-ray emission that the Fermi-LAT team proposed are either protons (hadronic model) or electrons (leptonic model), both of which were accelerated at the nova shock via the Fermi acceleration mechanism. We did not consider their leptonic model because no TeV gamma-ray emission is predicted. Their hadronic model can generate TeV gamma-rays with the modeled parameters. We found no evidence for TeV emission. We showed that with the flux upper limit calculated using the VERITAS data imposes constraints on the extension of the proton spectrum at high energies.

The main results of this work are the contribution to find the following results: <br />• The most general GRB is made by an early emission (P-GRB or Proper-GRB), with a time-scale not larger than 1 or 2 seconds and an afterglow, whose light curve is characterized by an increasing phase followed by a peak and a decreasing phase. This peak has been identified with the long GRBs prompt emission. In this scenario short GRBs are not but P-GRB, while long GRBs present both a peak and a decreasing late time emission, which is the observed afterglow.<br />• A possible GRB/SuperNova connection is based on the process of induced gravitational collapse of a companion star of the black hole originating the GRB. <br />• A thermal distribution in the comoving frame of the expanding system is assumed for X and γ bands of the spectrum. This assumption leads to a natural bending of the late time light curves making not necessary the hypothesis of a beamed emission within a collimated jet from the inner engine, which has been introduced in literature essentially to reduce the energy requirements.

En tant que dernière étape de l'évolution stellaire, les supernovae sont un outil fondamental pour appréhender l'évolution des galaxies. Elles constituent en effet le mécanisme principal d'enrichissement du milieu interstellaire en éléments de masse intermédiaire (comme l'oxygène, via les supernovae gravitationnelles ou de type II/Ib/Ic) et en éléments du pic du fer (grâce aux supernovae thermonucléaires ou de type Ia). De fait, la connaissance du taux de supernova, c'est-à-dire le nombre d'explosions par unité de temps et de volume ou de luminosité galactique est particulièrement intéressante pour comprendre l'évolution chimique des galaxies. <br> Depuis une dizaine d'années la recherche systématique de supernovae a pris un nouveau tournant grâce aux caméras CCD qui permettent d'obtenir des échantillons homogènes et peu biaisés. La recherche se fait directement par soustraction d'images prises à un mois d'intervalle. C'est dans ce cadre-là que l'expérience EROS, qui utilise un télescope de 1 mètre basé au Chili avec deux caméras CCD grand champ, a dédié pendant 4 ans environ 15% de son temps à la recherche de supernovae proches. L'analyse présentée ici a été effectuée à partir de deux campagnes d'observation par EROS, en 1999 et en 2000, avec l'aide de collaborations internationales afin de disposer de suffisamment de temps de télescope pour suivre l'évolution des supernovae détectées. Au total une quinzaine de supernovae de type Ia ont été découvertes par EROS. <br> La mesure de l'efficacité de détection, à l'aide d'une simulation de type Monte-Carlo, permet de mesurer le taux d'explosion de supernova de type Ia dans un domaine de décalage spectral proche ($z \sim 0.13$). La valeur obtenue est $0.23^(+0.09+0.07)_(-0.05-0.07)\ h^2$ SNu où 1 SNu = 1 SN / $10^(10)\ \text(L)_(\odot)^B$ / siècle. Cette valeur est compatible avec la précédente mesure effectuée par EROS, avec une statistique moindre, dans cette gamme de décalage spectral. Elle est à comparer avec la mesure réalisée par le 'Supernova Cosmology Project' à $z \sim 0.55$ où le taux est $0.58^(+0.10\ +0.10)_(-0.09\ -0.09)\ h^2$ SNu. La différence entre ces mesures implique une évolution relativement importante entre ces deux époques.

<p><p>Med utgångspunkt från den teoretiska bakgrunden, definitionen av svarta hål och deras generella egenskaper har jag studerat villkor för bildandet av svarta hål från döende singulära stjärnor. Supernovaprocessen beskrivs tillsammans med hur neutronstjärnor kan påverkas av destabiliserande mekanismer som t.ex. kaonkondensation. Olika observationer samt alternativa teorier läggs fram som argument och motargument. Utifrån detta underlag drar jag slutsatsen att svarta hål kan existera i fler varianter än vad som hittills antagits, främst i form av s.k. lågmassiva svarta hål på 1,5-1,8 M_sol.</p><p> </p><p>Vidare skildras möjligheten att producera mikroskopiska svarta hål i LHC-acceleratorn (Large Hadron Collider) i CERN, de kontroverser som omgärdar detta fenomen och de kunskaper som skulle kunna vinnas från kontrollerade observationer av sådana objekt. Den generella slutsatsen här är det ofrånkomliga mötet mellan partikelfysik och astrofysik för att få tillgång till de allra djupaste insikterna om det universum vi lever i.</p></p> / <p>Building on the theoretical background, definition of black holes and their general characteristics, I have studied some conditions for the formation of black holes from dying singular stars. The supernova process is described along with the influence on neutron stars by destabilising mechanism such as kaon condensation. Various observations as well as alternative theories are presented for argumentation. From this material I draw the conclusion that black holes can exist in more varieties than has been previously assumed, foremost in the shape of low-massive black holes with masses between 1.5 and 1.8 M_sun.</p><p> </p><p>Furthermore the possibility to produce microscopic black holes in the LHC accelerator (Large Hadron Collider) at CERN is portrayed, together with the controversies that currently surround this phenomenon and the knowledge that could be won from controlled observations of such objects. The general conclusion here is the unavoidable meeting between particle physics and astrophysics in order to access the deepest insights about the Universe we inhabit.</p>

Supernovae are known to be the dominant energy source for driving turbulence in the interstellar medium. Yet, their effect on magnetic field amplification in spiral galaxies is still poorly understood. Analytical models based on the uncorrelated-ensemble approach predicted that any created field will be expelled from the disk before a significant amplification can occur. By means of direct simulations of supernova-driven turbulence, we demonstrate that this is not the case. Accounting for vertical stratification and galactic differential rotation, we find an exponential amplification of the mean field on timescales of 100Myr. The self-consistent numerical verification of such a “fast dynamo” is highly beneficial in explaining the observed strong magnetic fields in young galaxies. We, furthermore, highlight the importance of rotation in the generation of helicity by showing that a similar mechanism based on Cartesian shear does not lead to a sustained amplification of the mean magnetic field. This finding impressively confirms the classical picture of a dynamo based on cyclonic turbulence. / Supernovae sind bekanntermaßen die dominante treibende Energiequelle für Turbulenz im interstellaren Medium. Dennoch ist ihre Auswirkung auf die Verstärkung von Magnetfeldern in Spiralgalaxien weitestgehend unverstanden. Analytische Modelle, die auf der Annahme eines unkorrelierten Ensembles beruhen, sagen voraus, dass das erzeugte Feld aus der galaktischen Scheibe herausgedrängt wird bevor eine substantielle Verstärkung erfolgen kann. Mithilfe numerischer Simulationen supernovagetriebener Turbulenz zeigen wir, dass dies nicht der Fall ist. Unter Berücksichtigung einer vertikalen Schichtung und differentieller galaktischer Rotation beobachten wir eine exponentielle Verstärkung des mittleren Magnetfeldes auf einer Zeitskala von 100 Mio. Jahren. Diese selbstkonsistente numerische Bestätigung eines “schnellen Dynamos” erlaubt es, die beobachteten starken Magnetfelder in jungen Galaxien zu erklären. Darüberhinaus stellen wir die Wichtigkeit der Rotation bei der Erzeugung von Helizität heraus, indem wir zeigen, dass ein ähnlicher Effekt basierend auf kartesischer Scherung nicht zu einer Verstärkung des mittleren Magnetfeldes führt. Dies bestätigt eindrucksvoll das klassische Bild zyklonischer Turbulenz.

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