In this thesis, we present our two studies focused on the detection of cosmic γ-rays and the analysis of data from γ-ray observations. One study deals with the method of the Cherenkov transparency coefficient. This method is suitable for the detector calibration in experiments employing imaging atmo- spheric Cherenkov telescopes for the indirect detection of cosmic γ-rays. Us- ing rates of recorded air showers initiated by charged cosmic rays, the method aims at the monitoring of the atmospheric transparency to Cherenkov light and the calibration of the responses of Cherenkov telescopes. We present an extension of this method for the purposes of the Cherenkov Telescope Array observatory and demonstrate its feasibility using Monte Carlo simu- lations. Our other analysis utilizes more than 7 years of data from direct γ-ray observations by the Fermi Large Area Telescope. We describe in detail signal observed from the parts of the sky around the active galactic nuclei 1ES 0229+200 and Centaurus A. We report on the findings of new astro- physical sources of high energy photons and document spectral and temporal properties of their γ-ray fluxes. 1

In this thesis, I present the properties of IRAS 19306+1407 central source and its sur- rounding circumstellar envelope (CSE), from the analysis of near-infrared (near-IR) polarimetry and integral field spectroscopy (IFS), with supporting archived HST im- ages and sub-millimetre (sub-mm) photometry. This is supported by axi-symmetric light scattering (ALS), axi-symmetric radiative transfer (DART) and molecular hy-drogen (H2) shock models. The polarimetric images show that IRAS 19306+1407 has a dusty torus, which deviates from axisymmetry and exhibits a ‘twist’ feature. The DART and ALS modelling shows that the CSE consists of Oxygen-rich sub-micrometre dust grains, with a range in temperature from 130±30 to 40±20 K at the inner and outer radius, respectively, with inner and outer radii of 1.9±0.1×1014 and 2.7±0.1×1015 m. The CSE detached 400±10 years ago and the mass loss lasted 5700±160 years, assuming a constant asymptotic giant branch (AGB) outflow speed of 15 km s−1. The dust mass and total mass of the CSE is 8.9±5×10−4 and 1.8±1.0×10 −1 M⊙, assuming a gas-to-dust ratio of 200. The mass loss rate was 3.4±2.1×10−5 M⊙ year−1. The central source is consistent with a B1I-type star with a radius of 3.8 ± 0.6 R⊙, luminosity of 4500 ± 340 L⊙ at a distance of 2.7 ± 0.1 kpc. A purpose built idl package (fus) was developed and used in the SINFONI IFS data critical final reduction steps. It also produced emission line, kinematic and line ratio images. The IFS observations show that H2 is detected throughout the CSE, located in bright arcs and in the bipolar lobes. The velocity of the H2 is greatest at the end of the lobes. Brγ emission originates from, or close, to the central source – produced by a fast jump (J) shock or photo-ionised atomic gas. The 1-0 S(1)/2- 1 S(1) and 1-0 S(1)/3-2 S(3) ratios were used as a diagnostic and determined that H2 was excited by bow shaped shocks; however, these shock models could not wholly explain the observed rotational and vibrational temperatures. The CDR values were fitted by combining continuous (C) or J-bow shock and fluorescence models, with a contribution from the latter, observed throughout the CSE (5–77 per cent). The majority of shock can be described by a C-bow shock model with B = 0.02 to 1.28 mG. Shocks are predominately seen in the equatorial regions. Polarimetry and IFS highlight a ‘twist’ feature, which could be due to an episodic jet undergoing a recent change in the outflow direction. The sub-arcsecond IFS observations reveal a flocculent structure in the south- east bright arc, consisting of several clumps interpreted as a fast-wind eroding an equatorial torus, possibly forming H2 knots seen in (some) evolved planetary nebulae (PNe). My analysis has effectively constrained the following: spectral type, stellar radius, luminosity and distance, chemistry, dust grain properties, geometry, age, mass loss, excitation mechanism and evolutionary state of the post-AGB star and its surrounding CSE. I conclude that IRAS 19306+1407 is a post-AGB object on the verge becoming a PN.

Le Large Area Telescope (LAT) à bord du satellite Fermi, lancé le 11 Juin 2008, est sensible au rayonnement gamma de20 MeV à plus de 300 GeV. 148 pulsars gamma à ce jour ont été détectés avec le Fermi-LAT, dont 117 sont détaillés dansle Deuxième Catalogue de Pulsars gamma de Fermi (2PC). Les pulsars forment la plus grande classe de sources au GeVdans la Voie Lactée. Les études de pulsars gamma apportent des contraintes importantes sur les modèles d’émission gamma etpermettent des percées dans notre compréhension des pulsars.Cette thèse présente des détections de sept pulsars gamma faibles déjà connus en radio, dont quatre jeunes ou d’âgesmoyens et trois millisecondes (MSP). L’analyse spectrale et la caractérisation des courbes de lumiére sont décriteset comparées à la population de 2PC. Ces détections ont l’intérêt particulier de sonder et d’étendre l’espace desparamètres de la population actuelle. Elles illustrent la distorsion inhérente dans 2PC et marquent la transition de lapremière phase (pulsars brillants) à la seconde phase (pulsars faibles) d’opération de Fermi. Le développement desmodèles théoriques et un recensement complet de la population galactique des étoiles à neutrons bénéficieront de plusde détections de pulsars faibles dans les années à venir.Certains pulsars gamma dans 2PC manifestant de grande efficacité gamma sont étudiés dans cette thèse. L’examen desdifférents paramètres qui influencent l’efficacité conduit à quelques candidats pour lesquels un plus grand momentd’inertie est nécessaire afin de résoudre le paradoxe de grande efficacité. Les observations de Fermi en rayons gamma ontl’air à apporter des contraintes indépendantes sur le moment d’inertie et les équations d’état des étoiles à neutrons. / The Large Area Telescope (LAT) on board the Fermi satellite, launched on June 11 2008, is sensitive to g raysfrom 20 MeV to over 300 GeV. gamma-ray pulsations from 148 pulsars to date have been detected with the Fermi-LAT, 117are detailed in the Second Fermi-LAT Gamma-ray Pulsar Catalog (2PC). Pulsars are by far the largest GeV sourceclassin the Milky Way. Studies of the increasing gamma-ray pulsar sample bring important constraints on theoretical gamma-rayemission models and enable breakthroughs in our understanding of pulsars.This thesis presents detections of seven faint gamma-ray pulsars that are already known at radio wavelengths, includingfour young or middle aged pulsars and three millisecond pulsars (MSPs). Spectral analysis and light curve characterizationsare detailed and compared to the 2PC sample. These detections have the special interest of allowing us toprobe and extend the parameter space of the current population. They illustrate the inherent bias in 2PC and mark thetransition from the early part (bright pulsars) to the later part (faint pulsars) of the Fermi mission. Theoretical modeldevelopments and a complete census of Galactic neutron star populations will benefit from more detections of weakpulsars in the years to come.Some high gamma-ray efficiency pulsars in 2PC are studied in this thesis. Investigations on different parameters whichinfluence the efficiency result in a few candidates for which a large moment of inertia is necessary to cure the highefficiency paradox. Fermi gamma-ray observations seem to bring independent constraints on the moment of inertia andequations of state of neutron stars

Le satellite Fermi a été lancé le 11 juin 2008, avec à son bord le Large Area Telescope (LAT). Le LAT est un télescope sensible au rayonnement ? de 20 MeV à plus de 300 GeV. Avant la mise en service du LAT, six pulsars jeunes et énergétiques étaient connus dans le domaine ? . Le nombre de détections de pulsars par le LAT prédit avant lancement était de plusieurs dizaines au moins. Le LAT permettait également l’étude des pulsars milliseconde (MSPs), jamais détectés avec certitude à très haute énergie jusqu’alors. Cette thèse aborde dans un premier temps la campagne de chronométrie des pulsars émetteurs radio et/ou X, candidats à la détection par le LAT, en collaboration avec les grands radiotélescopes et télescopes X. Cette campagne a permis la recherche de signaux ? pulsés avec une grande sensibilité. En outre, la plupart des MSPs galactiques ont été suivis dans le cadre de cette campagne, sans biais de sélection a priori sur cette population d’étoiles. Pour la première fois, des pulsations ont été détectées pour huit MSPs galactiques au-dessus de 100 MeV. Quelques bons candidats à une détection prochaine apparaissent. Une recherche similaire a été conduite pour des MSPs d’amas globulaires, sans succès à présent. L’analyse des courbes de lumière et des propriétés spectrales des huit MSPs détectés révèle que leur rayonnement ? est relativement similaire à celui des pulsars ordinaires, et est vraisemblablement produit dans la magnétosphère externe. Cette découverte suggère que certaines sources non-identi?ées sont des MSPs, pour l’instant inconnus. / The Fermi observatory was launched on June 11, 2008. It hosts the Large Area Telescope (LAT), sensitive to ? -ray photons from 20 MeV to over 300 GeV. Before the LAT began its activity, six young and energetic pulsars were known in ? rays. At least several tens of pulsar detections by the LAT were predicted before launch. The LAT also allowed the study of millisecond pulsars (MSPs), never ?rmly detected in ? rays before Fermi. This thesis ?rst presents the pulsar timing campaign for the LAT, in collaboration with large radiotelescopes and X-ray telescopes, allowing for high sensitivity pulsed searches. Furthermore, it lead to quasi-homogeneous coverage of the galactic MSPs, so that the search for pulsations in LAT data for this population of stars was not affected by an a priori bias. We present a search for pulsations from these objects in LAT data. For the ?rst time, eight galactic MSPs have been detected as sources of pulsed ? -ray emission over 100 MeV. In addition, a couple of good candidates for future detection are seen. A similar search for globular cluster MSPs has not succeeded so far. Comparison of the phase-aligned ? -ray and radio light curves, as well as the spectral shapes, leads to the conclusion that their ? -ray emission is similar to that of normal pulsars, and is probably produced in the outer-magnetosphere. This discovery suggests that many unresolved ?-ray sources are unknown MSPs.

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.

Dark matter (DM), whose nature and interaction mechanisms are still an open issue, constitutes about 25 % of the Universe energy density. Weakly Interacting Massive Particles (WIMPs) are considered as strong candidates for particle DM and their search is conveniently carried out through the detection of gamma rays. The newly discovered ultra-faint dwarf spheroidal galaxies (dSphs), located in the vicinity of the Galaxy, exhibit high values of the mass to luminosity ratio, and are therefore considered as strongly dominated by DM. These objects are within reach of the Cherenkov Telescope Array (CTA), which is the future project for gamma-ray astronomy, with an better sensitivity (one order of magnitude) with respect to the current generation experiments. The main goal of the present work is the study of the sensitivity of CTA to WIMPs DM particles, by simulating the observation of the ultra-faint dwarf spherical galaxies Triangulum II, Reticulum II and Carina III, as well as of the classical dwarf galaxy Sculptor, for different annihilation channels, between 70 GeV and 100 TeV. The sensitivity curve in the WIMPs parameter space (velocity-averaged annihilation cross section < &sigma; &nu; > and DM mass mDM) was computed. We found that, within the sample of dwarf galaxies tested, Triangulum II is the most promising source, able to reach the thermal freeze-out values in the annihilation channel &tau;+&tau;- for only 50 hours of observation. Our result, the first estimation of the sensitivity for DM searches in ultra-faint dwarfs with CTA, is consistent with results from current generation experiments, showing better performance over an extended energy range. The limited sample of available stars in the targets induces uncertainties on the DM content. Future measurements, leading to a better understanding of the sources dynamic equilibrium, can improve this situation. Even so, the combination of the high DM content in the ultra-faint dwarf galaxies, together with the excellent expected performance of the future CTA, provides a promising result for indirect DM searches. / A matéria escura, cuja natureza e mecanismos de interação ainda estão em aberto, compõe 25% da densidade de energia do Universo. Weakly Interacting Massive Particles (WIMPs) apresentam-se como forte candidatas e sua busca é convenientemente conduzida através de raios gama. As recém descobertas galáxias esferoidais anãs ultra-fracas, situadas nos arredores da Galáxia, apresentam altos valores da razão entre massa e luminosidade, sendo portanto consideradas objetos fortemente dominados por matéria escura. Esses objetos estão ao alcance do Cherenkov Telescope Array (CTA), que é o futuro projeto da astronomia gama, com sensibilidade de uma order de grandeza melhor do que os experimentos atuais. O presente trabalho teve como objetivo estudar o potencial de detecção indireta de WIMPs através de raios gama com o futuro observatório CTA, observando as galáxias esferoidais anãs ultra-fracas Triangulum II, Retículum II e Carina III e a galáxia anã clássica Sculptor, para diferentes canais de aniquilação, entre 70 GeV e 100 TeV. A curva de sensibilidade no espaço de parâmetros livres de WIMPs (massa da partícula mDM e médida da seção de choque de aniquilação ponderada pela velocidade < &sigma; &nu; >) foi calculada. Nós encontramos que dentro da amostra de galáxias anãs testadas, Triangulum II é a fonte mais promissora, capaz de testar os valores térmicos no canal de aniquilação &tau;+&tau;- considerando apenas 50 horas de observação pelo CTA. Nosso resultado, a primeira estimativa da sensibilidade para busca de matéria escura em galáxias esferoidais anãs ultra-fracas com CTA, é consistente com resultados de experimentos da geração atual, e mostra um melhor desempenho em uma faixa de energia estendida. Os resultados são afetados pelas incertezas devido à pequena amostra de estrelas dos alvos escolhidos, que se reflete no conhecimento do conteúdo de matéria escura. Novas medidas podem ajudar a esclarecer essa situação. Ainda assim, a combinação de galáxias anãs ultra-fracas, aliada às melhorias do futuro CTA, apresenta-se como um passo muito promissor para buscas indiretas de matéria escura.

We present a detailed study of mid-infrared spectroscopy and optical imaging of Seyfert galaxies with the goal of understanding the properties of astronomical dust around the central supermassive black hole and the accretion disk. Specifically, we have studied Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8-1.9s and 58 Seyfert 1s and 2s available in the Spitzer public archive, and the nuclear dust morphology in the central 500 pc of 91 narrow and broad-line Seyfert 1s using optical images from the Hubble Space Telescope. We have also developed visualization software to aid the understanding of the geometry of the central engine. Based on these studies, we conclude that the nuclear regions of Seyfert galaxies are fueled by dusty spirals driven by the large-scale stellar bars in the host galaxy. The accumulation of dusty gas in the central kiloparsec leads to enhanced star formation. In this case, the circumnuclear starburst and the central engine compete for dominance in the heating of the circumnuclear dust. Emission from the heated dust is most clearly seen in the mid-infrared. We find that the spectra of Seyfert 2s show the most variety in the continuum shapes due to different starburst contributions. We find that the spectra of Seyfert 2s that are devoid of starburst contribution are dominated by a single thermal component at a temperature of T ~ 170 K. We also find that the mid-IR continua of Seyfert 1.8/1.9 galaxies are more like those of starburst-dominated Seyfert 2s than Seyfert 1s, contrary to expectations. We discuss the implications of these findings in the context of the Unified Model of AGN and the secular evolution of Seyfert nuclei.

In this thesis I describe the development of a compact camera for ground-based multi TeV gamma-ray astronomy, using the Imaging Atmospheric Cherenkov Telescope (IACT) technique. The camera is based on multi-anode photomultipliers (MAPM) and is designed for use on the Gamma Cherenkov Telescope (GCT), which is proposed to be part of the Small Size Telescope (SST) array of the Cherenkov Telescope Array (CTA). GCT achieves high performance with a compact and cost efficient design via a Schwarzschild-Couder (SC) dual-mirror optical system. The GCT optical design allows the use of a compact camera of diameter roughly 0.5 m. The curved focal plane is equipped with 32 tiles of 64-pixels MAPM for a total of 2048 pixels of ~0.2° angular size, resulting in a field of view of ~9°. The GCT camera is designed to record the flashes of Cherenkov light from electromagnetic cascades, which last only a few tens of nanoseconds. I give a detailed description of the design, the challenges encountered during testing in the lab, and the performance of the most critical components. I give details on the custom front-end electronics modules that provide the required fast electronics, facilitating sampling and digitization, as well as first level of triggering. The camera-level triggering system is a custom backplane, developed to reject spurious triggers on the night sky background, which typically is of the order of few tens of millions of photons per pixel per second. This is to be compared with the rate of the astrophysical signal, which is of the order of few hundreds of events per second at the relevant energies. Additionally I provide a detailed description of all the software needed for the data acquisition and control of the camera, from the very low level drivers to high level and user friendly processes. I follow the commissioning of the camera, from the individual core components to the integration of the system. I then describe the integration of the camera on the GCT prototype telescope structure, and the achievement of "first light", validating for the first time the full proof-of-concept of an IACT with SC optics. I also report a study I performed on expectations for an extragalactic survey for blazars with CTA. The cumulative source count distribution of blazars is presented, including implications from two different phenomena: axion-like particle (ALP) to gamma-ray oscillations in the intergalactic magnetic field, and secondary gamma rays from hadronic origins. I conclude that a shallow and wide survey will provide the best science return for CTA, that the impact of ALP is modest and that the secondary mechanism of gamma-ray production would allow detection of blazars up to redshift of 1 in the multi-TeV energy band.

La prise en compte et la correction des effets induits dans les images par les détecteurs du plan focal (CCD) a été identifié comme étant un point essentiel pour remplir les objectifs scientifiques de la collaboration LSST- Dark Energy Science Collaboration. Le groupe de travail SAWG a été crée, et des bancs optique ont été mis à contribution dans certains laboratoires de la collaboration (UC Davis, SLAC, BNL et LPNHE) afin d'adresser le problème. LSST fait partie d'une nouvelle catégorie de télescopes : les grands plans focaux. Depuis une dizaine d'années que ceux-ci sont équipés de CCD à haute résistivité, un certain nombre de nouveaux effets ont été identifiés. Une attention toute particulière est portée sur la compréhension des distorsions électrostatiques inhérentes aux propriétés du CCD qui ont un impact sur les mesures de science. Le travail de cette thèse est centré sur l'étude de l'effet brighter-fatter et des tree-rings. Il a été démontré qu'avec certains types d'illuminations, il était possible de caractériser ces effets avec précision. C'est dans le but de produire ces illuminations qu'un projecteur de franges a été développé sur le banc optique du LPNHE. Dans ce document sont ainsi présentés : une nouvelle méthode de caractérisation des tree- rings testée sur des simulations ; une nouvelle méthode de mesure de l'effet brighter-fatter basée sur la projection de profils de Ronchi ; une étude complète des différentes propriétés de l'effet brighter-fatter dans laquelle a été mis en place un modèle électrostatique simplifié. Enfin, l'efficacité d'une méthode de correction, dite de descrambling est évaluée. / The removal of the sensor signature in the science images has been identified by the LSST Dark Energy Science Collaboration as a mandatory path to fullfill its scientific goals. The SAWG working group has been put together to perform this task for the collaboration. It has access to optical benches in some of the laboratories of the collaboration (UC Davis, SLAC, BNL and LPNHE) for this purpose. LSST belongs to a new category of telescopes equiped with large focal planes. For the decade that they have been equipped with thick, high resistivity Charge Coupled Devices (CCD), new effects have been identified. A particular attention is given to the understanding of the electrostatic distortions that are inherent to the CCD properties. These electrostatic distortions have an impact on science measurements. My PhD work is centered on the study of the brighter-fatter effect and the tree-rings. It has been shown that with different kind of illuminations, it was possible to accurately characterize these effects. A fringe projector has been developed on the optical bench of the LPNHE in order to produce these particular illuminations. In this document, we present : a new method, tested on simulations, to characterize the tree-rings; a new method to measure the brighter-fatter effect based on the projection of Ronchi profiles; a complete study of the different properties of the brighter-fatter effect, where we developped a simplified electrostatic model. Finally, the efficiency of a correction method, called descrambling, is evaluated.

No description available.