Recentemente, o Observatório Pierre Auger tem medido espectro de energia de Raios Cósmicos Ultra Energéticos (Ultra High Energy Cosmic Rays - UHECR) (E > 1019 eV) com grande acurácia. No entanto, o estudo de raios cósmicos ultra energéticos na Terra tem uma forte dependência do estudo de sua propagação no Universo. Neste trabalho, abordamos o estudo da propagação de raios cósmicos em diferentes aspectos. Núcleos em alta energia interagem com os campos de radiação no caminho da fonte à Terra. A interação mais importante é a fotodesintegração. Na primeira parte, implementamos de maneira analítica e numérica a solução da razão de fotodesintegração e fizemos uso da solução numérica em um programa de Monte Carlo. Mostramos soluções baseadas na parametrização das seções de choque por uma função Gaussiana e por uma função Lorenztiana. Comparamos nossos resultados com trabalhos prévios da literatura. O seguinte estudo mostrou que sob a hipótese de propagação quase-linear e utilizando várias distribuições de fontes no céu, a latitude do observatório: tem influência no fluxo total medido por um observatório; impõe um limite na capacidade de medida de anisotropia e tem um efeito negligenciável na medida do XMax. No terceiro estudo, um limite superior na integral do fluxo de raios gama em GeV-TeV é usado para obter um limite superior na luminosidade total de UHECR de fontes individuais. A correlação entre o limite superior na integral do fluxo de raios gama e o limite superior na luminosidade total de UHECR é estabelecida através do processo de cascatas de partículas geradas durante a propagação de raios cósmicos nos campos de radiação. / Recently, the Pierre Auger Observatory has measured the energy spectrum of Ultra High Energy Cosmic Rays (UHECR) (E > 1019 eV) with an unprecedented accuracy. However, the study of ultra-high energy cosmic rays at Earth depends on the models used to describe the propagation of the particle in the Universe. In this work, we present a study of propagation of cosmic rays on different aspects. Nucleus at this high energy interacts with the radiation fields on the way from the source to Earth. The most important interaction is the photodisintegration. In the first part, we implemented analytical, numerical and Monte Carlo simulation solutions for the photodisintegration rate. We show solutions based on parameterizations of the cross-section using Gaussian and Lorenztian functions. We compare our results with previous works. The following study shows that under the assumption of quasi-linear propagation and using several sources distributions of sky, the latitude of the observatory: has influence on the total flux measured by an observatory; imposes a limitation on the capability of measuring an anisotropic sky and has a negligible efect on the Xmax measurement. In the thirdy study, an upper limit on the integral flux of GeV-TeV gamma-rays is used to extract the upper limit on the total UHECR luminosity of individual sources. The correlation between upper limit on the integral GeV-TeV gamma-rays flux and upper limit on the UHECR luminosity is established through the cascading process that takes place during propagation of the cosmic-rays in the background radiation fields.

Das Fermi Large Area Telescope (LAT) ist ein satellitengestütztes Gammastrahlungs-Teleskop zur Messung von Gammastrahlung im Energiebereich zwischen ∼ 30 MeV und mehreren hundert GeV. Der Nachweis extraterrestrischer Gammastrahlung in diesem Energiebereich erlaubt Rückschlüsse auf die astrophysikalischen Quellen der Gammastrahlung und Beschleunigungsmechanismen kosmischer Strahlung mit Energien zwischen 1 GeV und ∼ 10 TeV. Die Beobachtung von Quellen während Phasen vorübergehend erhöhter Gammastrahlungslüsse (‘Flares’) ermöglicht dabei eine besonders empfindliche Untersuchung der Produktionsmechanismen kosmischer Strahlung in den Quellen, da die Eigenschaften kürzlich beschleunigter Teilchen unmittelbar studiert werden können. Der Hauptteil dieser Dissertation stellt das neueste Verzeichnis zeitlich variabler Gammastrahlungsquellen über 100 MeV vor, den zweiten ‘Fermi All-sky Variability Analysis’ Katalog (2FAV). Der 2FAV Katalog enthält über 4500 Flares, welche in den ersten 7.4 Jahren der LAT Datennahme auf einem hohen Vertrauensniveau gemessen und an 518 verschiedenen Himmelspositionen beobachtet wurden. 441 dieser Quellpositionen im 2FAV können Aktiven Galaktischen Kernen (AGN) zugeordnet werden. Die verbleibenden 77 Quellpositionen besitzen keine sichere Entsprechung in anderen Verzeichnissen von Gammastrahlungs- oder Blazarquellen und stellen möglicherweise neue Gammastrahlungsquellen dar. Bei der Untersuchung der Spektren der 2FAV Flares, welche sogenannten ‘Flat-Spectrum’ Radioquasaren (FSRQ) - eine Unterklasse der AGN - zugeordnet werden können, wurde durchweg ein härteres Gammastrahlungsspektrum während Phasen erhöhter Gammastrahlungsemission beobachtet. Zudem wurde eine Untergrenze in der Verteilung der spektralen Exponenten, Γ ≳ 1.5, in der Stichprobe der untersuchten Flares festgestellt. Unter der Annahme eines einfachen leptonischen Modells und dass die Verteilung beschleunigter Teilchen im Inertialsystem der Quelle isotrop ist, folgt daraus, dass die Energiespektren der kosmischen Strahlung, welche die Gammastrahlungs-Flares verursachen, mit dN/dE ∝ E −2 oder stärker abfallen. Eine andere Möglichkeit, die Beschleunigungsmechanismen kosmischer Strahlung zu untersuchen, ist die Messung der Polarisation der begleitenden Gammastrahlung. Der letzte Teil dieser Dissertation enthält eine vorläufige Studie zur Messbarkeit linearer Polarisation astrophysikalischer Gammastrahlung mit dem LAT-Instrument. Bei Konversion hochenergetischer Photonen in Elektron-Positron-Paare verursacht eine lineare Polarisation der Gammastrahlung eine Modulation des Azimutwinkels der Ebenen, in denen die Elektron-Positron-Paare erzeugt wurden. Obwohl der LAT ursprünglich nicht als Polarimeter konzipiert wurde, ermöglicht das Instrument eine Messung dieser Modulation für niederenergetische Primärteilchen (≲ 200 MeV), welche in den Silikonschichten des Detektors konvertieren. Eine Auswahl solcher Ereignisse, selektiert durch Algorithmen überwachten maschinelles Lernens (‘supervised machine learning’), wird verwendet um die statistischen und systematischen Messunsicherheiten abzuschätzen, denen eine Messung unterworfen ist. Werden allein statistische Unsicherheiten berücksichtigt, ist der LAT in der Lage, einen Polarisationsgrad von 30−50% der Gammastrahlungsflüsse vom Vela-Pulsar und vom Krebs-Pulsarwindnebels nach einer Beobachtungszeit von zehn Jahren auf einem Vertrauensniveau von 5σ nachzuweisen. Werden zusätzlich systematische Unsicherheiten berücksichtigt, wird abgeschätzt, dass ein Polarisationsgrad von ∼ 46% auf einem Vertrauensniveau von 5σ nachweisbar ist, indem eine Auswahl von AGN als unpolarisierte Testprobe verwendet und mit umfangreichen Monte-Carlo Simulationen verglichen wird. Die Analyse in dieser Dissertation berücksichtigt zum ersten Mal sämtliche Aspekte einer polarization-sensitiven Ereignissrekonstruktion und dienst damit als Grundlage für zukünftige Nachweisversuche der Polarisation astrophysikalischer Gammastrahlung mit dem LAT. / The Fermi Large Area Telescope (LAT) is a space-based pair-conversion telescope sensitive to gamma rays with energies from ∼ 30 MeV to several hundreds of GeV. Observing gamma rays in this energy range, we gain information on the sources and acceleration mechanisms of cosmic rays (CRs) of energies from ∼ 1 GeV to ∼ 10 TeV. Studying the emission of gamma-ray sources during periods of enhanced activity (flares) provides a sensitive probe of the production mechanisms of CRs, as it makes it possible to investigate the distributions of the freshly-accelerated particles. The main part of this work presents the latest catalog of variable gamma-ray sources above 100 MeV, the second Fermi All-sky Variability Analysis catalog (2FAV). The 2FAV catalog contains more than 4500 flares detected at high significance in the first 7.4 years of LAT observations and the 518 sources from which these flares originate. Probable counterparts, mostly active galactic nuclei (AGN), have been found for 441 sources in the 2FAV. The remaining 77 sources have no reliable counterparts in other gamma-ray or blazar catalogs; they are potentially new gamma-ray sources. Studying the spectra of the 2FAV flares, we observe a harder-when-brighter behavior for the entire sample of flares associated with lat spectrum radio quasars, a class of AGN. We also observe a minimum value in the distribution of the photon index Γ of the flares, corresponding to Γ ≳ 1.5. In a simple leptonic scenario, assuming that the distribution of accelerated particles is isotropic in the source reference frame, this limit on the spectral hardness implies that the spectra of the accelerated particles responsible for the lare is never harder than dN/dE ∝ E −2. Another way to probe the environments where CRs are accelerated is by measuring the polarization of the gamma rays. A preliminary study of the LAT sensitivity to linear polarization of astrophysical gamma-rays is presented in the last part of this thesis. In the pair-production regime, linear polarization of the gamma-rays induces a modulation in the azimuthal angle of the planes where the electron-positron pairs are produced. Although not designed as a polarimeter, the LAT has the potential to measure this modulation using low energy (≲ 200 MeV) events converting in the silicon detector layers of its tracker. A selection of these events using supervised machine learning algorithms is presented and used as a basis to estimate the statistical and systematic uncertainties afecting the measurement. Considering only statistical uncertainties, a degree of polarization of ∼ 30−50% could be detected at the 5σ confidence level for the Vela pulsar and the Crab pulsar-wind nebula after 10 years of observation. By including systematic uncertainties, a 5σ sensitivity limit corresponding to a polarization degree of ∼ 46% is estimated, using a stack of AGN as an unpolarized test source and comparing the data with detailed Monte Carlo simulations. This analysis addresses for the first time all the steps of a real measurement and can therefore provide the basis for future measurements of gamma-ray polarization with the LAT.

Es wird angenommen, dass schalenartige Supernova-Reste wesentlicheQuellen der galaktischen kosmischen Strahlung sind. Die Beschleunigungvon Teilchen in diesen Objekten kann mit hochenergetischerGammastrahlung (Energien zwischen 30GeV und 30TeV) nachgewiesenwerden.In dieser Arbeit wird die Beobachtung von Gammastrahlung desschalenartigen Supernova-Restes RX J0852.0-4622 beschrieben. DieseBeobachtungen wurden im Februar 2004 mit dem High Energy StereoscopicSystem (H.E.S.S.) durchgeführt. H.E.S.S., ein System von vierabbildenden Cherenkov Teleskopen, kann Gammastrahlung im Bereichzwischen 100GeV und einigen 10TeV nachweisen und ist zur Zeit dasleistungsfähigste Instrument in diesem Energiebereich.Die Emission von Gammastrahlung von RX J0852.0-4622 wurde mit einerSignifikanz von 12 sigma bei einer Belichtungszeit von 3.2hnachgewiesen. Die Morphologie der Emissionsregion ist ausgedehnt undkorreliert mit der Morphologie der Röntgenstrahlung. Eindifferenzielles Energiespektrum des Photonenflusses wurde im Bereichzwischen 0.5 und 10 TeV rekonstruiert. Das Spektrum folgt einemPotenzgesetz mit einem spektralen Index von etwa 2.1. Der integriertePhotonenfluss oberhalb von 1 TeV ist auf dem Niveau des Flusses desKrebsnebels. RX J0852.0-4622 ist daher eine der hellstenGammastrahlungsquellen am Himmel und der zweite Supernova-Rest dessenausgedehnte Gammastrahlungsemission nachgewiesen werden konnte.Gammastrahlung kann durch inverse Compton-Streuung vonrelativistischen Elektronen oder durch starke Wechselwirkungen vonProtonen mit dem interstellaren Material erklärt werden. Der erwarteteEnergiefluss von inverser Compton-Streuung an der kosmischenMikrowellenstrahlung wurde abgeschätzt. Dieser ist um einigeGrößenordnungen geringer als der beobachtete Wert. Daher ist eswahrscheinlich, dass die beobachtete Gammastrahlung ausProton-Wechselwirkungen stammt und RX J0852.0-4622 zur galaktischenkosmischen Strahlung beiträgt. / Shell-type supernova remnants are discussed to be a main source of thegalactic cosmic rays. Very high energy gamma rays (energies between30GeV and 30TeV) from these objects are tracers for the accelerationof particles. Up to now, only a limited number of supernova remnantswere observed in gamma rays. This work reports on the observations of gamma rays from theshell-type supernova remnant RX J0852.0-4622 carried out with the HighEnergy Stereoscopic System (H.E.S.S.) in February 2004. H.E.S.S., asystem of four imaging Cherenkov telescopes, is dedicated to theobservation of gamma rays of energies between 100GeV and several tensof TeV and it is currently the most sensitive instrument in thisenergy range.Emission of gamma rays from RX J0852.0-4622 was detected with asignificance of 12 sigma within a live time of 3.2h. The morphologyof the emission region is clearly extended and correlated with themorphology of the X-ray emission. A differential energy spectrum ofthe photon flux between 0.5 and 10 TeV was reconstructed. It is foundto follow a power law with a spectral index of about 2.1. The integralphoton flux above 1 TeV is at the level of the Crab flux at theseenergies. Thus, RX J0852.0-4622 is one of the brightest gamma-raysources in the sky. RX J0852.0-4622 is the second supernova remnant ofwhich an extended gamma-ray morphology could be proved.The emission of gamma rays from shell-type supernova remnants can beexplained as being produced by accelerated electrons or protons. Theexpected energy flux due to inverse Compton scattering of relativisticelectrons on the cosmic microwave background was estimated and foundto be several orders of magnitude lower than the observed flux. Thus,it is likely that the observed gamma-ray emission is produced inproton interactions and that RX J0852.0-4622 contributes to theacceleration of galactic cosmic rays.

An environmental friendly and simple approach to synthesis of Platinum (Pt), Palladium (Pd), Rhodium (Rh) and Osmium (Os) nanoparticles via gamma radiolysis is demonstrated. Herein, we report on the effect of gamma rays radiation on Platinum (Pt), Osmium (Os), Rhodium (Rh) and Palladium (Pd) salts solutions for synthesis of nanoparticles. Pt, Os, Rh and Pd salts solutions of different concentrations were exposed to intense gamma rays irradiation with doses varying from 70 to 120 kGy. The metal ion salt solutions were easily converted into metal nanoparticles (MNP) using radiolysis method. The radiolytic conversion effect produced MNP suspended in the solution. For Pt, Pd and Rh a metal coating on the edges of the polypropylene tube used as a container, was unexpectedly observed but not for the Os solution. Physical/chemical properties of γ-ray produced nanoparticles were reported. UV-Vis spectroscopy, X-ray diffraction (XRD) and High resolution transmission electron microscopy (HRTEM) analyses confirmed that both the coating and the MNP correspond to the pure metal coming from the reduction of the initial salt. HRTEM analysis shows the particles size and particle distribution of the produced nanoparticles. Quantitative analysis of the XRD patterns shows information about the size and stress of the converted metals. The functional groups in the solvent are analysed by Fourier Transform Infrared spectroscopy (FTIR). The production of a metal coating on polypropylene plastic tubes by gamma-rays irradiation is presenting an interesting alternative to conventional techniques of metal deposition especially for coating the inner part of a tube. / Physics / D. Lit. et Phil. (Physics)

Le LAT est l'instrument principal du satellite Fermi et permet d'étudier le ciel en rayons gamma de 20 MeV à plus de 300 GeV. Sa sensibilité accrue a permis l'augmentation du nombre de sources détectées dans le domaine des hautes énergies. Une partie importante de celles-ci n'a pas de contrepartie connue et une étude multi-longueur d'onde est nécessaire afin de comprendre l'origine du signal observé. Dans un premier temps, cette thèse présente l'étude morphologique et spectrale détaillée de la source non-identifiée HESS J1745--303, qui a été découverte dans le domaine gamma par l'expérience H.E.S.S. en 2006 puis analysée spécifiquement dans un article de 2008, à l'aide des données du LAT. Deux sources ponctuelles situées à une localisation proche de HESS J1745-303 sont présentes dans le catalogue à deux ans de données de Fermi (2FGL) mais une analyse dédiée de cette région est néanmoins nécessaire vu sa complexité. Elle est en effet localisée à ~1° du Centre Galactique et à moins de 0.5° du pulsar de la Souris, les deux sources les plus brillantes en gamma dans cette région.Les différents processus d'émission de photons sont présentés dans un second temps. Leurs simulations permettent d'effectuer une étude approfondie de l'origine de l'émission détectée aux hautes et très hautes énergies par le LAT et par H.E.S.S. L'émission de cette source reste en effet encore énigmatique de nos jours et une étude multi-longueur d'onde est effectuée afin de contraindre les modèles d'émission. / The LAT is the main instrument onboard the Fermi space telescope and performs unprecedented observations of the gamma-ray sky between 20 MeV and more than 300 GeV. The number of gamma-ray sources detected has grown thanks to its high sensibility. A large part of these sources has no known counterpart and a multi-wavelength study is needed in order to understand the origin of the observed signal.This thesis presents a morphological and spectral detailed study of the unidentified source HESS J1745--303, which was discovered in gamma-rays in 2006 with the H.E.S.S. experiment, using the Fermi-LAT data. Two point-like sources, located near HESS J1745--303, are included in the Fermi Large Area Telescope Second Source Catalog (2FGL) but, due to the complexity of this region, a dedicated study of the LAT data is however needed. Indeed, its location is ~1° away from the Galactic Center source and less than 0.5° from the Mouse pulsar, the two brightest gamma-ray sources in this region.The astrophysical emission processes are then detailed. We develop an extensive code which allowed us to study the origin of the HE (High Energy) and VHE (Very-High Energy) gamma-ray emissions detected by the LAT and H.E.S.S. The emission of this source is indeed still enigmatic and we perform a mutli-wavelength study to try to constrain the emission modeling.

Embora seja uma técnica tradicional, empregada largamente em processos industriais, a operação unitária de aeração pode ser otimizada ao se utilizar modelos matemáticos que descrevam seu comportamento hidrodinâmico. Diversas equações se prestam a esse fim, no entanto, avanços tecnológicos, tanto no campo instrumental como computacional, permitiram a obtenção de equações mais realísticas e abrangentes. Neste trabalho foram ajustadas e avaliadas equações para descrever três importantes parâmetros envolvidos na transferência de oxigênio em meio hídrico: coeficiente volumétrico de transferência de massa, fração de vazios e velocidade ascensional de bolhas. Para tanto, ademais da utilização de conceitos teóricos amplamente difundidos no meio acadêmico, empregou-se um conjunto de dados já existente. Essa combinação permitiu a avaliação e aproximação das equações teóricas à realidade experimental através de coeficientes de ajuste empíricos. Foram obtidos os seguintes resultados: a) revisão bibliográfica e sugestão da correlação que melhor descreve o coeficiente volumétrico de transferência de massa; b) correlação que descreve a fração de vazios, a partir da analise da concentração de bolhas segundo distribuições gaussianas; c) correlação que descreve a velocidade ascensional de bolhas em plumas. A complexidade de cada parâmetro obtido deixou clara a importância da análise isolada, precedendo a convolução dos mesmos em um único modelo, pois embora as resposta e recomendações apresentadas não forneçam conclusões definitivas sobre todos os aspectos envolvidos na transferência de oxigênio em meio hídrico, suas considerações pontuais contribuem sobremaneira ao domínio do fenômeno global, beneficiando modelagens matemáticas futuras. / Although it is a traditional technique, widely employed in industrial processes, the unit operation of aeration can be optimized when resorting to mathematical models which describe their hydrodynamic behavior. A range of equations lends itself to this purpose, however, technological advances both in the instrumental as computational field, allowed the achievement of equations more realistic and comprehensives. In this study were adjusted and evaluated equations to describe three important parameters involved in the oxygen transfer in the hydric medium: volumetric mass transfer coefficient, void fraction and upflow bubble velocity. To this end, besides the use of theoretical concepts widely disseminated in the academic literature, it was employed a set of already existing data. This combination allowed the evaluation and approximation of theoretical equations to experimental reality by means of empirical adjustment coefficients. Were obtained the following results: a) literature review and suggestion of the best correlation which describes the volumetric mass transfer coefficient, b) correlation which describes the fraction of voids, from the analysis of the concentration of bubbles by Gaussian distributions, c) correlation which describes the upflow velocity of swarms of bubbles. The complexity of each parameter obtained made clear the importance of the isolated analysis, preceding the convolution of them in a single model because although the answers and recommendations given fail to supply definitive conclusions on all aspects involved in the transfer of oxygen in hydric medium, their specific considerations contribute to the knowledge of the global phenomenon, benefiting deeply future mathematical models.

Dans le domaine de l’astrophysique des hautes énergies, de nombreuses questions restent à ce jour sans réponse et, parmi elles se trouve l’origine des rayons cosmiques Galactiques. La première preuve observationnelle de ces particules accélérées a été apportée au sein d’un vestige de supernova il y a seulement vingt ans. Depuis, nous savons que les vestiges de supernova, les pulsars et leurs nébuleuses accélèrent efficacement des particules mais de nombreuses interrogations subsistent encore. Les preuves directes concernant l’accélération de protons (constituant 90% du rayonnement cosmique) sont rares et de nombreuses sources nouvellement détectées en gamma sont de nature inconnue. Les rayonnements produits au sein des accélérateurs Galactiques fournissent d’importants éléments de réponse quant à la nature des particules accélérées. En particulier, alors que les domaines de la radio et des rayons X ne tracent que les électrons accélérés, les rayons gamma peuvent inférer la présence d’électrons et également de protons (et noyaux en général) mais l’émission s’avère le plus souvent difficile à interpréter.Les mesures des rayons gamma de très hautes énergies dépendent de notre connaissance de l’atmosphère terrestre, dans lequel ils se propagent avant d’être détectés par les télescopes Tcherenkov au sol tels que le réseau H.E.S.S. La partie technique de cette thèse concerne l’étude de l’impact des profils d’atmosphère sur les données H.E.S.S. Grâce à des simulations et des analyses prenant en compte les caractéristiques propres à chaque prise de données, nous étudions l’impact des profils d’atmosphère mesurés sur les fonctions de réponse de l’instrument et sur la reconstruction spectrale.Le premier objectif scientifique de cette thèse est de comprendre la nature de l’émission gamma au sein de deux vestiges de supernova (G326.3-1.8 et RX J1713.7-3946) par le biais d’analyses spectro-morphologiques détaillées. L’analyse de G326.3-1.8, avec les données du Fermi-LAT, a mené à deux résultats importants: une nouvelle preuve d’accélération de protons et la première séparation morphologique et spectrale de deux composantes imbriquées en gamma. L’analyse de RX J1713.7-3946, avec les données H.E.S.S. et les outils d'analyse Ctools, a confirmé une extension plus importante en gamma qu’en rayons X mais dont l’origine reste encore incertaine.La deuxième partie de cette thèse entreprend de discuter la nature des sources Galactiques non-associées au TeV. Pour ce faire, nous présentons un code générique visant à rechercher des contreparties multi-longueurs d’onde sur ces sources au TeV, et permettant de poser des contraintes sur des paramètres physiques tels que le champ magnétique moyen et l’indice spectral en radio. En appliquant ce code sur cinq sources non-identifiées du relevé du plan Galactique de H.E.S.S., nous apportons des arguments quant à leur origine. En particulier, nous étudions deux sources, dont l’émission au TeV provient probablement de multiples contributions, soulevant ainsi l’importance des données multi-longueurs d’onde pour comprendre la nature de l’émission en gamma. / In high energy astrophysics, several questions are still open and amongst them is the origin of Galactic cosmic rays. The first observational evidence of accelerated particles has only been revealed twenty years ago. Since then, supernova remnants, pulsars and their nebulae are known to efficiently accelerate particles but several questions still hold. In particular, evidence of accelerated protons (which consist on 90% of the cosmic-ray spectrum) is still elusive and several gamma-ray sources have unknown origin. Non-thermal emissions produced in Galactic accelerators provide insights about the nature of the accelerated particles. In particular, while radio and X-ray observations indicate the presence of accelerated electrons, gamma rays can be produced by both electrons and protons (or nuclei in general) but it may be difficult to assess the origin of the emission.The technical part of this thesis concerns the study of the impact on the reconstructed H.E.S.S. data when using atmospheric profiles measured with a lidar instead of a standard atmospheric model currently used. Very high energy gamma rays propagate into the atmosphere before reaching Cherenkov Telescopes and thus, the accuracy of our measurements depends on our understanding of the atmospheric composition. Using run-wise simulations based on lidar data, we study the impact on the instrument response functions and we analyse data to quantify the effect on the spectral reconstruction.The first scientific goal of this thesis is to understand the gamma-ray emission from two supernova remnants (G326.3-1.8 et RX J1713-3946) through detailed spectro-morphological analyses. The analysis of the composite supernova remnant G326.3-1.8, with Fermi-LAT data, has led to two major results: a new evidence of accelerated protons and the first morphological and spectral separation in gamma rays of two nested components. The study of RX J1713-3946, with H.E.S.S. data and using the Ctools package, confirms a significant gamma-ray extension beyond the X-ray emitting shell but its origin remains unclear.The second part of this thesis aims to constrain the nature of the unidentified TeV sources revealed in the H.E.S.S. Galactic Plane Survey. We thus present a generic code, based on a multi-wavelength approach, to find counterparts and estimate physical parameters like the radio spectral index and the mean magnetic field. We apply this code on five unidentified TeV sources and we put constraints on their nature. In particular, we present two high-confusion cases, for which the TeV emission is probably due to the contribution from different components, emphasizing the importance of multi-wavelength data to understand the origin of the gamma-ray emission.

A new formalism is presented for calculating the mean intensity spectrum and angular power spectrum of gamma-rays or neutrinos from extragalactic annihilating dark matter, taking into account the dependence of the relative motions of the annihilating particles on the annihilation cross section. To model the large scale dark matter distribution of mass and relative velocities, the halo distribution model is comprehensively summarized, and extended to include a universal radial profile of the particles' velocity variance, based on results from N-body computer simulations of dark matter halos. A velocity variance profile, associated with the NFW density profile, is proposed by enforcing a power-law profile of the pseudo phase-space density. This allows the large-scale velocity distribution to be described by virialized, gravitationally bound dark matter halos, as opposed to thermal motions used to describe the velocity distribution in the early Universe. The recent particle motion history of the Universe is presented for the described model. Sample extragalactic gamma-ray intensities from dark matter annihilation are shown for dark matter annihilating with p-wave, according to a relative-velocity-weighted annihilation cross section sigmav = a + bv^2, for constants a and b, with examples taken from supersymmetric models. For thermally produced dark matter, the p-wave suppresses the signal intensity. If b/a > 10^6, the p-wave hardens the intensity spectrum by an estimated factor of 1 + (6b/a)delta_I (E_gamma), and increases the angular power spectrum by a factor also depending on new coefficients (delta_Cl)^(1) (E_gamma ) and (delta_Cl)^(2) (E_gamma ). The energy-dependence of the new p-wave coefficients delta_I , (delta_Cl)^(1) (E_gamma ), and (delta_Cl)^(2) (E_gamma ) are shown for various annihilation spectra. Sample intensity spectra are also presented for Sommerfeld-enhanced annihilation. The intensity of neutrinos from dark matter annihilation is also considered. The variations between the dark matter annihilation signals for different particle phenomenologies suggest that particle physics constraints are possible from an observed indirect detection signal. Calculations of the annihilation signal from the galactic halo are also shown. The extragalactic signal's intensity is found to be consistent in magnitude with the galactic intensity?within the uncertainty of the models of the dark matter distribution?when looking out from the galactic plane. This suggests that the total cosmic signal may have significant contributions from both components.

De nombreuses observations astrophysiques indiquent l'existence de grandes quantités de masse manquante dans l'Univers, et ce de l'échelle galactique à l'échelle cosmologique. Découvrir la nature de cette masse invisible constitue le problème de la matière noire, qui apparaît comme l'un des enjeux majeurs de la physique moderne. Cette thèse s'inscrit dans le contexte de la détection indirecte de matière noire. Cette dernière serait composée de nouvelles particules élémentaires, dont les produits d'annihilation pourraient être observés dans le rayonnement cosmique. Nous étudions dans ce travail deux des canaux de recherche les plus prometteurs : les photons gamma et les anti-noyaux.Les objets astrophysiques permettant de placer les meilleures contraintes actuelles en rayons gamma sont les galaxies naines sphéroïdes (dSphs) de la Voie Lactée. La première partie de notre travail a été consacrée à contraindre les facteurs J d'annihilation de ces objets, qui quantifient l'amplitude des flux gamma attendus. Nous avons pour cela mis au point une configuration optimisée d'analyse de Jeans, pour reconstruire les profils de densité de matière noire et leurs incertitudes à l'aide des données cinématiques stellaires. Notre configuration a été obtenue à l'aide de tests systématiques sur de très nombreuses dSphs simulées, et nous l'avons appliquée à vingt-trois dSphs de la Voie Lactée. La seconde partie de notre travail a consisté à mener une recherche de noyaux d'anti-hélium dans les données collectées par l'expérience AMS-02 sur la Station Spatiale Internationale. Nous avons pour cela mis au point une classification par arbres de décision boostés, et notre analyse préliminaire a permis d'obtenir les meilleures contraintes actuelles sur les rapports anti-hélium sur hélium. / Many astrophysical observations suggest the existence of large amounts of missing mass in the Universe, from the galactic to the cosmological scale. Discovering the nature of this invisible mass forms the dark matter problem, which appears as one of the major challenges of modern physics. This thesis is established in the context of indirect detection of dark matter. The latter could consist of new elementary particles, whose annihilation products may be observed in cosmic rays. We study in this work two of the most promising research channels!: gamma-rays and anti-nuclei.The best constraints on dark matter properties from gamma-ray observations come from the dwarf spheroidal galaxies (dSphs) of the Milky Way. The first part of our work was devoted to computing the annihilation J-factors of these objects, which quantify the magnitude of the expected gamma-ray flux. We have developed an optimized Jeans analysis setup in order to reconstruct the dark matter density profiles of these objects and their associated uncertainties, using stellar kinematic data. Our optimized setup was obtained using systematic tests on numerous simulated dSphs, and we applied it to twenty-three dSphs of the Milky Way. The second part of our work was dedicated to the search for anti-helium nuclei in the cosmic ray data collected by the AMS-02 experiment on the International Space Station. We have developed a classification method using boosted decision trees, and our preliminary analysis has led to the best constraints to date on the anti-helium to helium ratio.

Recentemente, o Observatório Pierre Auger tem medido espectro de energia de Raios Cósmicos Ultra Energéticos (Ultra High Energy Cosmic Rays - UHECR) (E > 1019 eV) com grande acurácia. No entanto, o estudo de raios cósmicos ultra energéticos na Terra tem uma forte dependência do estudo de sua propagação no Universo. Neste trabalho, abordamos o estudo da propagação de raios cósmicos em diferentes aspectos. Núcleos em alta energia interagem com os campos de radiação no caminho da fonte à Terra. A interação mais importante é a fotodesintegração. Na primeira parte, implementamos de maneira analítica e numérica a solução da razão de fotodesintegração e fizemos uso da solução numérica em um programa de Monte Carlo. Mostramos soluções baseadas na parametrização das seções de choque por uma função Gaussiana e por uma função Lorenztiana. Comparamos nossos resultados com trabalhos prévios da literatura. O seguinte estudo mostrou que sob a hipótese de propagação quase-linear e utilizando várias distribuições de fontes no céu, a latitude do observatório: tem influência no fluxo total medido por um observatório; impõe um limite na capacidade de medida de anisotropia e tem um efeito negligenciável na medida do XMax. No terceiro estudo, um limite superior na integral do fluxo de raios gama em GeV-TeV é usado para obter um limite superior na luminosidade total de UHECR de fontes individuais. A correlação entre o limite superior na integral do fluxo de raios gama e o limite superior na luminosidade total de UHECR é estabelecida através do processo de cascatas de partículas geradas durante a propagação de raios cósmicos nos campos de radiação. / Recently, the Pierre Auger Observatory has measured the energy spectrum of Ultra High Energy Cosmic Rays (UHECR) (E > 1019 eV) with an unprecedented accuracy. However, the study of ultra-high energy cosmic rays at Earth depends on the models used to describe the propagation of the particle in the Universe. In this work, we present a study of propagation of cosmic rays on different aspects. Nucleus at this high energy interacts with the radiation fields on the way from the source to Earth. The most important interaction is the photodisintegration. In the first part, we implemented analytical, numerical and Monte Carlo simulation solutions for the photodisintegration rate. We show solutions based on parameterizations of the cross-section using Gaussian and Lorenztian functions. We compare our results with previous works. The following study shows that under the assumption of quasi-linear propagation and using several sources distributions of sky, the latitude of the observatory: has influence on the total flux measured by an observatory; imposes a limitation on the capability of measuring an anisotropic sky and has a negligible efect on the Xmax measurement. In the thirdy study, an upper limit on the integral flux of GeV-TeV gamma-rays is used to extract the upper limit on the total UHECR luminosity of individual sources. The correlation between upper limit on the integral GeV-TeV gamma-rays flux and upper limit on the UHECR luminosity is established through the cascading process that takes place during propagation of the cosmic-rays in the background radiation fields.