Detection techniques for the H.E.S.S. II telescope, data modeling of gravitational lensing and emission of blazars in HE-VHE astronomy

La présente thèse porte sur quatre aspects différents de l astronomie des hautes énergies.La première partie de ma thèse est dédiée à un développement instrumental pour les télescopes Cherenkov imageurs, le système de déclenchement de niveau 2 du télescope de 28 mètres du réseau H.E.S.S. (High Energy Stereoscopic System). Mon travail s est focalisé sur l invention d algorithmes et les simulations Monte-Carlo du système de déclenchement, ainsi que la comparaison de la reconstruction au niveau de la carte de déclenchement à la reconstruction hors-ligne (Moudden,Barnacka, Glicenstein et al. 2011a; Moudden, Venault, Barnacka et al. 2011b). Je décris le système et j évalue ses performances.Le réseau H.E.S.S. a observé le blazar PKS1510-089. La deuxième partie de ma thèse traite de l analyse des données et la modélisation de l émission large bande de ce blazar. C est un exemple de quasar radio à spectre plat (FSRQ), pour lequel il n est attendu aucune émission aux très hautes énergiesJ ai modélisé les données observées pendant un "flare de PKS1510-089. Ce modèle est basé sur un scénario de choc interne à une zone.Le troisième chapitre de ma thèse est une étude d un autre phénomène affectant potentiellement les blazars observés par FERMI-LAT: l effet de lentille gravitationnelle fort. Cette partie de ma thèse montre le premier indice de présence d un effet de lentille gravitationnelle dans le domaine des photons de haute énergie. Cet indice provient de l observation d un écho dans la courbe de lumière du blazar distant PKS1830-211, qui est une lentille gravitationnelle connue. Les méthodes d estimation des retards temporels dans les systèmes de lentille gravitationnelles reposent sur la corrélation croisée des courbes de lumière individuelles. Dans l analyse présentée dans cette thèse, j ai utilisé des photons de 300 MeV à 30 GeV détectés par l instrument FERMI-LAT. L instrument FERMI-LAT ne peut pas séparer spatialement les images des lentilles gravitationnelles fortes connues. La courbe de lumière observée est donc la superposition des courbes de lumière des images individuelles. Les données du FERMI-LAT ont l avantage d être des séries temporelles régulièrement espacées,avec un bruit de photons très bas. Cela permet d utiliser directement les méthodes de transformées de Fourier. Un retard temporel entre les images compactes de PKS1830-211 a été recherché par deux méthodes : une méthode d auto-corrélation et la méthode du double spectre . La méthode du double spectre fournit un signal de 27 +- 0.6jours (statistique) avec une significativité de 4.2 . Ce résultat est compatible avec ceux de Lovell et al (1998) et Wiklind et Combes (2001).La dernière partie de ma thèse est consacrée à un effet de lentille différent, le femtolensing . La recherche d effets de femtolensing a été utlisée pour obtenir des limites sur l abondance de trous noirs primordiaux. Celle-ci a été contrainte de manière significative dans un large domaine de masses. Les limites les moins contraignantes ont été établies pour les objets de faible masse, pour lesquels la détection représente un défi expérimental. J ai utilisé les sursauts gamma de redshift connus d etectés par le Fermi Gamma Ray Burst Monitor (GBM) pour rechercher d éventuels effets de femtolensing produits par des objets compacts sur la ligne de visée. L absence de ces effets de femtolensing montre que des trous noirs primordiaux de masse comprises entre 5.10^17 et 10^20 g ne constituent pas une fraction importante de la matière noire. J ai effectué mes études de thèse en co-tutelle entre le Centre Astronomique Nicolaus Copernicus de l académie des sciences polonaise, à Varsovie et l Institut de Recherches sur les Lois fondamentales de l Univers du CNRS à Saclay, en France.This thesis presents the study of four aspects of high energy astronomy.The first part of my thesis is dedicated to an aspect of instrument development for imaging atmospheric Cherenkov telescopes, namely the Level 2 trigger system of the High Energy Stereoscopic System (H.E.S.S.). My work on the project focused on the algorithm development and the Monte Carlo simulations of the trigger system and overall instrument (Moudden, Barnacka, Glicenstein et al. 2011a; Moudden, Venault, Barnacka et al. 2011b). The hardware implementation of the system is described andits expected performances are then evaluated. The H.E.S.S. array has been used to observe the blazar PKS 1510-089.The second part of my thesis deals with the data analysis and modeling of broad-band emission of this particular blazar. In part II of my thesis, I am presenting the analysis of the H.E.S.S. data: the light curve and spectrum of PKS 1510-089, together with the FERMI data and a collection of multi-wavelength data obtained with various instruments. I am presenting the model of PKS 1510-089 observations carried out during a flare recorded by H.E.S.S.. The model is based on a single zone internal shock scenario.The third part of my thesis deals with blazars observed by the FERMI-LAT, but from the point of view of other phenomena: a strong gravitational lensing. This part of my thesis shows the first evidence for gravitational lensing phenomena in high energy gamma-rays. This evidence comes from the observation of a gravitational lens system induced echo in the light curve of the distant blazar PKS 1830-211. Traditionalmethods for the estimation of time delays in gravitational lensing systems rely on the cross-correlation of the light curves from individual images. In my thesis, I used 300 MeV-30 GeV photons detected by the Fermi-LAT instrument. The FERMI-LAT instrument cannot separate the images of known lenses. The observed light curve is thus the superposition of individual image light curves. The FERMI-LAT instrument has the advantage of providing long, evenly spaced, time series with very low photonnoise. This allows to use directly Fourier transform methods. A time delay between the two compact images of PKS 1830-211 has been searchedfor both by the autocorrelation method and a new method: the double power spectrum . The double power spectrum shows a 4.2 evidence for a time delay of 27.1+-0.6 days (Barnacka et al. 2011), consistent with the results from Lovell et al. (1998) and Wiklind & Combes (2001).The last part of my thesis concentrates on another lensing phenomena called femtolensing . The search for femtolensing effects has been used to derive limits on the primordial black holes abundance. The abundance of primordial black holes is currently significantly constrained in a wide range of masses. The weakest limits are established for the small mass objects, where the small intensity of the associated physical phenomenon provides a challenge for current experiments. I have usedgamma-ray bursts with known redshifts detected by the FERMI Gamma-ray Burst Monitor (GBM) to search for the femtolensing effects caused by compact objects. The lack of femtolensing detection in the GBM data provides new evidence that primordial black holes in the mass range 5 . 10^17 10^20 g do not constitute a major fraction of dark matter (Barnacka et al. 2012). My Ph.D. studies have been carried out jointly between the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, in Warsaw in Poland and the IRFU institute of the Commissariat à l énergie atomique et aux énergies alternatives(CEA) Saclay in France.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Diverse perspectives of parents, diverse concepts of parent involvement and participation: Contrasts between Italy and the United States

Diversity of experiences and perspectives, it is widely agreed, should be a source of strength in home-school partnerships, as in other aspects of educational endeavor. Yet often, in the literature, diversity is presented as a complication to be overcome. A limiting mindset often prevails, both in theory and practice, where diversity is regarded as an issue or barrier, even amidst the best of intentions to be inclusive. In this chapter, we argue that this limiting mindset on diversity may in fact derive in part from the conceptual frameworks with which we in the United States contemplate and conduct research on diversity issues in home-school relationships. We make this point by taking the discussion outside the framework of the American literature. First, we offer our summary and interpretation of several general principles that describe the purpose, nature, and value attached to parental involvement in the United States. Next, we turn to the field of Italian education, in particular, to conceptualizations about partecipazione, or participation, a term for the idealized way in which parents, teachers, and community members should take an active part in the life, culture, and decisions concerning children and the educational services created for them. We draw mainly from the writings of a network of early educational leaders from cities of northern and central Italy (e.g., Bologna, Milan, Modena, Pistoia, Reggio Emilia, and others)—places which have carried out the strongest experiments in creating and sustaining systems of home-school-community

Search for Primordial Black Hole evaporations with H.E.S.S

International audienceFollowing LIGO results of intermediate mass black holes mergers, the idea that dark matter is composed of Primordial Black Boles (PBH), made a recent comeback.PBHs might be formed in the early Universe through a variety of mechanisms, best known being the gravitationalcollapse of overdense regions due to density fluctuations. It's widely accepted that black hole loose there mass over time through the Hawking radiation process.Since the particle emission rate increases with black hole temperature, PBHevaporation is a runaway process that eventually leads to a violent explosion. It has been argued that a class of ultra short gammay ray bursts are actually PBH explosions. The current upper limits on the local PBH explosion rate lie in the $10^4$--$10^5$ $\mathrm{pc}^{-3}$ $\mathrm{yr}^{-1}$ range.This contribution reports on the search for TeV $\gamma$-ray bursts with a timescale of a few seconds, as expected from the final stage of PBHs evaporation, using 2700 hours of H.E.S.S. extragalactic observations. We present the search algorithm, statistical estimations strategies and results of this analysis

Observations du centre galactique et recherche de signaux exotiques avec H.E.S.S.

L astronomie gamma des très hautes énergies a pour but d étudier l origine du rayonnement cosmique. Cette nouvelle discipline, née il y a une trentaine d années, sonde les mécanismes d accélération des particules chargées dans divers objets astrophysiques (pulsars, trous noirs, reste de supernovae ) via leur émission gamma . L astronomie gamma est aussi un formidable moyen pour la recherche de phénomènes exotiques et de nouvelle physique. Cette thèse se penche sur trois sujets de physique fondamentale qui peuvent être étudiés des très hautes énergies : l accélération des particules chargée au voisinage d un trou noir supermassif, l évaporation de trous noirs primordiaux, et enfin la recherche indirecte de matière noire. Le support commun à toutes ces études est l analyse des données récoltées par l expérience HESS (High Energy Stereoscopic System) qui observe le ciel dans le domaine des photons gamma d énergie supérieure à 100 GeV. Cette thèse présente tout d abord les aspects et les enjeux de l astronomie gamma des très hautes énergies ainsi que le fonctionnement du détecteur HESS. Les méthodes d analyse utilisées dans la suite pour interpréter les données sont aussi détaillées. Un premier sujet lié à l astrophysique des trous noirs est abordé dans cette thèse, et concerne les observations par HESS de la région du Centre Galactique. Les observations menées depuis 2004 ont mis en évidence une émission gamma dont l origine reste inconnue. Le spectre et la variabilité de la source gamma sont étudiés en détails pour essayer d interpréter le signal gamma en terme d accélération de particules au voisinage de Sgr A*, le trou noir supermassif situé au centre dynamique de la Voie Lactée. L ensemble des données récoltées par HESS est ensuite utilisé pour la recherche de sursauts de photons gamma signant l évaporation de trous noirs primordiaux. Les trous noirs primordiaux sont des objets exotiques qui peuvent avoir été créés lors des tous premiers instants de l Univers. L émission gamma au Centre Galactique empêche la détection d un éventuel signal de matière noire. A l instar du Centre Galactique, les galaxies naines sphéroïdales du groupe local sont des objets dépourvus de fond astrophysique et sont donc des cibles intéressantes. Dans la dernière partie de cette thèse, une présentation synthétique de nos connaissances actuelles sur les propriétés de la matière noire est faite. Les données prises par HESS en direction de la galaxie naine Canis Major du Sagittaire, sont alors interprétées en terme d annihilation de matière noire pour dériver des contraintes sur des modèles de physique des particules susceptibles de décrire ses propriétés.Very high gamma-ray astronomy is a new and young physics field which aims to study the origin of cosmic rays and their acceleration process inside various astrophysical objects such as pulsars, black holes or supernovae remnants. This is also a promising way to search for exotic high energy phenomena and unknown physics. This dissertation deals with three fundamental physics topics closely connected to very high energy gamma-ray astronomy : particle acceleration in the vicinity of a supermassive black hole, primordial black holes evaporation, and indirect searches for dark matter. Each of these topics studied with data collected by the HESS (High Energy Stereoscopic System ) instrument, an imaging Cherenkov array dedicated for the detection of very gamma-rays above 100 GeV. In the first part of the dissertation, we present a rapid overview of the field of very high energy gamma-ray astronomy. A precise description of the HESS detector is then given as well as the data analysis techniques used to derive the results that are subsequently presented. The first subject is related to black hole astrophysics and concerns observations of the Galactic Center region whith H.E.S.S. The source of the gamma-ray emission discovered in 2004 toward this region is unindentified. A precise determination of the source energy spectrum and variability with new data is reported here. Results are then compared with models of particle acceleration in the vicinity of Sgr A*, the supermassive black hole located at the dynamical center of the galaxy. In a second subject, the whole data collected with the H.E.S.S. are used to search for the signature of primordial black hole evaporation through their emission of burst of gamma-rays. Primordial black holes are exotic objects the might have formed in the early stages of the Universe. As the bulk of the gamma-ray emission is likely to originate from a standard astrophysical mechanism, the Galactic Center is not an ideal searches, because they are dominated by dark matter and they are devoid of any astrophysical emission. In the last part of this dissertation we first give an overview of our current knowledge about the dark matter properties. The next chapters are then devoted to the H.E.S.S. observations of the Canis Major and Sagittarius dwarf sphreroidal galaxies. The data analysis are used to constrain some dark matter models.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Status and performance results from NectarCAM -- a camera for CTA medium sized telescopes

International audienceThe Cherenkov Telescope Array (CTA) will be the first ground-based observatory for gamma-ray astronomy. With more than a hundred of 4th generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) distributed in two large arrays, CTA will reach unprecedented sensitivity, angular resolution, and spectral coverage.Three classes of IACT -- 40 Medium-Sized Telescopes (MSTs), 8 Large-Sized Telescopes (LSTs) and 70 Small-Sized Telescopes (SSTs) -- are required to cover the full CTA energy range (20 GeV to 300 TeV).NectarCAM is a Cherenkov camera which is designed to equip medium sized telescopes of CTA, covering the central energy range from 100 GeV to 30 TeV, with a field of view of 8 degrees. It's based on a modular design with data channels using the NECTAr chip, which are equipped with both GHz sampling Switched Capacitor Array and 12-bit Analog to Digital Converter (ADC). The camera will be equipped of 265 modules, each module consisting of 7 photomultiplier Tubes (PMTs) and a Front End Board performing the data capture, sending the data over the Ethernet after the trigger decision at rates up to 10 kHz.This contribution provides an overview of the status of the first NectarCAM camera currently under integration in Saclay. Furthermore, we will discuss the calibration strategies and present performance results from the Saclay test bench and from the first data taken under a real sky on the prototype of medium sized telescope (MST) structure in Adlershof

Searches for dark matter subhaloes with wide-field Cherenkov telescope surveys

The presence of substructures in dark matter haloes is an unavoidable consequence of the cold dark matter paradigm. Indirect signals from these objects have been extensively searched for with cosmic rays and γ rays. At first sight, Cherenkov telescopes seem not very well suited for such searches, due to their small fields of view and the random nature of the possible dark matter substructure positions in the sky. However, with long enough exposure and an adequate observation strategy, the very good sensitivity of this experimental technique allows us to constrain particle dark matter models. We confront here the sensitivity map of the HESS experiment built out of their Galactic scan survey to the state-of-the-art cosmological N-body simulation Via Lactea II. We obtain competitive constraints on the annihilation cross section, at the level of 10-24-10-23cm3s-1. The results are extrapolated to the future Cherenkov Telescope Array, in the cases of a Galactic plane survey and of an even wider extragalactic survey. In the latter case, it is shown that the sensitivity of the Cherenkov Telescope Array will be sufficient to reach the most natural particle dark matter models

Monte Carlo Simulations and Validation of NectarCAM, a Medium Sized Telescope Camera for CTA

International audienceThe upcoming Cherenkov Telescope Array (CTA) ground-based gamma-ray observatory will open up our view of the very high energy Universe, offering an improvement in sensitivity of 5-10 times that of previous experiments. NectarCAM is one of the proposed cameras for the Medium-Sized Telescopes (MST) which have been designed to cover the core energy range of CTA, from 100 GeV to 10 TeV. The final camera will be capable of GHz sampling and provide a field of view of 8 degrees with its 265 modules of 7 photomultiplier each (for a total of 1855 pixels). In order to validate the performance of NectarCAM, a partially equipped prototype has been constructed consisting of only the inner 61 modules. It has so far undergone testing at the integration test-bench facility in CEA Paris-Saclay (France) and on a prototype of the MST structure in Adlershof (Germany). To characterize the performance of the prototype, Monte Carlo simulations were conducted using a detailed model of the 61 module camera in the CORSIKA/sim_telarray framework. This contribution provides an overview of this work including the comparison of trigger and readout performance on test-bench data and trigger and image parameterization performance during on-sky measurements

Performance tests of the NectarCAM qualification model

International audienceThis contribution describes the laboratory characterization and calibration of the NectarCAM before deployment.NectarCAM is a camera developed to equip the medium-sized telescopes (MST) of the Cherenkov Telescope Ar-ray Observatory (CTAO). It is designed to detect Cherenkov light in the central energy range of the CTAO from100 GeV to 30 TeV, with a field of view of 8 degrees. It comprises 265 modules, each consisting of 7 photo-multiplier tubes (PMTs) and a Front-End Board performing the data capture. The sampling and digitizationof the signal is performed by the NECTAr chip, a switched capacitor array able to perform the sampling of thesignal at 1 GHz. We report here on the status of the NectarCAM camera, currently under integration in CEAParis-Saclay (France). The results of the ongoing timing performance tests will be presented

Monte Carlo Simulations and Validation of NectarCAM, a Medium Sized Telescope Camera for CTA

The upcoming Cherenkov Telescope Array (CTA) ground-based gamma-ray observatory will open up our view of the very high energy Universe, offering an improvement in sensitivity of 5-10 times that of previous experiments. NectarCAM is one of the proposed cameras for the Medium-Sized Telescopes (MST) which have been designed to cover the core energy range of CTA, from 100 GeV to 10 TeV. The final camera will be capable of GHz sampling and provide a field of view of 8 degrees with its 265 modules of 7 photomultiplier each (for a total of 1855 pixels). In order to validate the performance of NectarCAM, a partially-equipped prototype has been constructed consisting of only the inner 61-modules. It has so far undergone testing at the integration test-bench facility in CEA Paris-Saclay (France) and on a prototype of the MST structure in Adlershof (Germany). To characterize the performance of the prototype, Monte Carlo simulations were conducted using a detailed model of the 61 module camera in the CORSIKA/sim_telarray framework. This contribution provides an overview of this work including the comparison of trigger and readout performance on test-bench data and trigger and image parameterization performance during on-sky measurements. © Copyright owned by the author(s) under the terms of the Creative Commons