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Luashvili, Anna. "Étude de l’origine de la variabilité rapide dans les blazars". Electronic Thesis or Diss., Université Paris sciences et lettres, 2023. http://www.theses.fr/2023UPSLO014.
Pełny tekst źródłaAGN are the compact cores of galaxies which are referred to as active, when they show signs of matter accretion onto a super-massive black hole at their centre and development of relativistic jets, able to expel highly energetic particles at great distances from their centre. Their main characteristics are extremely luminous cores, which outshine the host galaxy radiation, and highly variable emission across the entire electromagnetic spectrum, from radio to very high, sometimes up to TeV energies, ascribed to non-thermal processes at play in the jet.Approximately 10% of AGN are found to be radio-loud, which exhibit a powerful jet and are divided into the groups of radio galaxies and blazars. In the case of blazars, the jet is closely aligned with the line of sight of the observer and due to relativistic effects, their radiation is heavily Doppler boosted and variability timescales are reduced in the observer’s frame, where high amplitude variability can be observed on timescales down to few minutes only. Such violent events are called flares, with the most spectacular outbursts being observed at the highest energies.In order to study the physical origin of rapid variability observed in blazars and AGN in general, a two-fold apporach is nessecary: coordination of extensive multi-wavelength monitoring programs of variable sources, with the ability to swiftly trigger follow-up observations in response to various alerts, in order to collect coherent sets of quasi-simultaneous data at different frequencies and next, their analysis and interpretation by means of radiative transfer models. In this thesis, I try to summarise my contribution to each of these steps.I had the pleasure to be part of the High Energy Stereoscopic System (HESS) collaboration, operating an imaging Cherenkov telescope array in Namibia, which allows us to detect extremely powerful irruptions in distant AGN at very high energies. I could participate in on-site observations, being part of the Target of Opportunity (ToO) group, where we track variable AGN, request and follow MWL observations and especially HESS triggers, which lead to many exciting discoveries over the years. Statistical characterisation of HESS-detected AGN flares and the study of an extremely variable blazar 3C 279 through its most spectacular flaring events detected at high and very high energies constitute my main contributions to two task forces in the AGN working group of HESS.This thesis starts with an introduction to the AGN family and our current vision of the unification scheme. It presents the different physical scenarios which are generally invoked to explain variability with different timescales in blazars and AGN in general. Next, radiative models are presented, suited for two sub-classes of blazars. Moreover, high and very high energy data analysis techniques, collected with Fermi telescope and HESS are detailed, necessary to constrain the radiative models. They are illustrated with the examples of major high and very high energy flare data sets of 3C 279.The modelling of various high energy gamma-ray activity states of a sample of peculiar Narrow-Line Seyfert 1 galaxies (which were not thought to be able to develop powerful jets), and the statistical characterisation of AGN flares detected with HESS constitute the major core of this thesis.Blazars are the dominant population of sources producing high energy gamma-rays. There is strong indication that they are emitters of high energy neutrinos and possibly ultra-high energy cosmic rays as well. They serve as natural laboratories for fundamental physics tests. Many questions still remain open and it is an exciting era for time-dependent and multi-messenger astronomy
Chernatkin, Vladimir. "Simulation des gerbes dues aux rayons cosmiques à très hautes énergies". Nantes, 2005. http://www.theses.fr/2005NANT2074.
Pełny tekst źródłaLorentz, Matthias. "Caractérisation de la transparence de l'univers aux rayons gamma de très haute énergie avec H.E.S.S. et aspects associés en physique fondamentale et cosmologie". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS249/document.
Pełny tekst źródłaThe propagation of very high energy Ɣ rays in the universe depends on the properties of the extragalactic medium. Such TeV-scale photons travelling cosmological distances are -emitted through particle acceleration mechanisms in active galaxy nuclei- can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. This effect reduces the transparency of the universe to very high energy Ɣ rays but it also provides a unique opportunity to probe the properties of the extragalactic medium. In this thesis, data taken with the H.E.S.S. array of Cherenkov telescopes are analyzed and used to characterize the transparency of the universe to very high energy Ɣ rays. A independent measurement of the spectral energy distribution of the EBL with H.E.S.S. is presented. It is obtained by extracting the EBL absorption signal from the fit of spectral modulations in the high-quality spectra of a sample of bright blazars in the redshift range 0.03 < z < 0.28. The intensity of the EBL obtained in different spectral bands is presented together with the associated Ɣ-ray horizon. The obtained results are consistent with lower limits derived from galaxy counts and do not suggest an anomaly of the transparency of the universe to Ɣ rays with respect to current models of the extragalactic background light. Second-order processes affecting the propagation of very high energy Ɣ rays in the universe are also considered. Limits on Lorentz invariance violation at Planck scale are obtained from the spectral analysis of the active galaxy nucleus Mrk 501 observed during a high-flux state by H.E.S.S. in 2014, at large zenith angle. Finally, constraints on the extragalactic magnetic field properties are derived by considering the secondary Ɣ-ray emission expected from the simulation of electromagnetic cascades initiated by the absorption process for the distant active galaxy nucleus PG 1553+113 seen by H.E.S.S. and the Fermi Ɣ-ray space telescope. In this thesis some developments related to the calibration and analysis of H.E.S.S. data are also presented
Jouvin, Lea. "Le centre Galactique aux très hautes énergies : modélisation de l’émission diffuse et premiers éléments d’analyse spectro-morphologique". Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC213/document.
Pełny tekst źródłaThe Galactic center (GC) is a very rich and complex astrophysical region. The high supernovae (SN) rate associated with the strong massive star formation should create a sustained cosmic rays (CR) injection in the GC via the shocks they produce. This region also harbors a Super-Massive Black Hole (SMBH) of $4 \times 10^6 \, \rm{M_{\odot}}$, named Sgr A*. Since it has been argued that the SMBH might also accelerate particles up to very high energies (VHE), its current and past activity could contribute to the CR population. In 2006, the H.E.S.S. collaboration revealed the presence of a VHE diffuse emission in the inner 100 pc of the Galaxy in close correlation with the molecular matter spread in the central molecular zone (CMZ). A major part of this emission is thus certainly of hadronic origin but it still remains mysterious. We report a new detailed spectral and morphological analysis of this region using 10 years of H.E.S.S. observations as well as a detailed modelling of the $\gamma$-ray emission induced by the SNe. We study the impact of the spatial and temporal distribution of SNe in the CMZ on the VHE emission morphology and spectrum: we built a 3D model of VHE CR injection and diffusive propagation with a realistic gas distribution. The contribution of SNe can not be neglected. We show that a peaked $\gamma$-ray profile and CR excess towards the GC, can be obtained using realistic SN spatial distribution taking into account the central massive star clusters. A strong dependence on the morphology of the emission with the energy is expected in this scenario. The CR density profile can also be reproduced by a unique stationary injection at the center by Sgr A* but it implies a stable morphology across the energy range. To distinguish the models, we need a 3D analysis. We present the first results of this analysis that we started to design in the software Gammapy to simultaneously fit a spectral and morphological model to the data. The observations of complex morphological regions with diffuse emission or multiple sources will become more and more numerous with the next generation instruments such as the Cherenkov Telescope Array. They will also require the development of this technique. We detail the first validations of this method on point sources using a Monte Carlo tool. For the ridge emission, we report the new spectrum using a method that we developed for the classical spectral fitting necessary for faint emission. By using new spatial templates to describe the complexity of the diffuse emission, we perform a morphological analysis in different energy bands independently. No significant variation is found but more observations are needed to give a conclusive statement as well as a real 3D analysis in the GC region. The observations of CTA will allow to give precise answers to these questions
Lenain, Jean-Philippe. "Rayonnement gamma des Noyaux Actifs de Galaxies observé aux Très Hautes Énergies avec H.E.S.S.: Études multi-longueurs d'onde et modélisation de processus radiatifs". Phd thesis, Observatoire de Paris, 2009. http://tel.archives-ouvertes.fr/tel-00431288.
Pełny tekst źródłaLenain, Jean-Philippe. "Rayonnement γ des noyaux actifs de galaxies observé aux très hautes énergies avec H. E. S. S. : études multi-longueurs d’onde et modélisation de processus radiatifs". Observatoire de Paris (1667-....), 2009. https://theses.hal.science/tel-00431288.
Pełny tekst źródłaActive Galactic Nuclei (AGN) are among the most energetic sources in the Universe. A subgroup of AGN possesses relativistic jets, the emission of which is purely non-thermal. In the case where the jet is aligned to the line of sight, these objects, called “blazars”, have their emission amplified by the relativistic Doppler effect. Since the advent of very high energy (VHE; E > 100GeV) -ray astrophysics, Čerenkov telescopes like H. E. S. S. Have observed almost thirty AGN, mainly blazars, from the ground. Čerenkov radiation from particle showers created by the interaction of -rays in the terrestrial atmosphere is used to derive the properties of the incident photon and thus to study these extragalactic sources. We have studied the highly variable VHE -ray emission from the blazar PKS 2155- 304, from which two major outbursts were detected in July 2006, within the framework of a dynamic Synchrotron self-Compton (SSC) model. This variable emission presents properties excluding the most standard emission scenarios for blazars. We have also developed an SSCemission model for misaligned relativistic jets, to interpret the recent discovery of VHE -ray emission from two radio galaxies, M87 and CenA, which established the emergence of a new familiy of cosmic TeV emitters. We conclude with a systematic study conducted on all the AGN currently known at TeV with a stationary SSC model. We present tools for predictions of flux densities in these objects, which can be confronted with future observations by the Čerenkov Telescope Array (CTA)
Zouari, Samuël. "Étude de l'origine de l'émission à très haute énergie au centre de notre galaxie et connexion possible avec Sgr A*, notre plus proche trou noir super-massif". Electronic Thesis or Diss., Université Paris Cité, 2023. http://www.theses.fr/2023UNIP7120.
Pełny tekst źródłaAt the Centre of our Galaxy lies a supermassive black hole named Sgr A*. The HESS experiment has been observing the region in very high energy gamma rays, and has detected a compact source HESS J1745-290, compatible in position with the black hole, as well as a diffuse emission, interpreted as a proof of an excess of energetic particles, freshly injected by a PeVatron. The key to understanding the origin of the diffusion emission is the establishment of an association between Sgr A* and the central source : its possible extension, its spectral behaviour and its possible time variations. Indeed, there are two objects compatible with the position of HESS J1745-290, which could theoretically emit very high energy gamma rays : Sgr A* and the pulsar nebula G359,95. This thesis will investigate these questions from a theoretical perspective and then through the analysis of the many data HESS has gather on the Galactic Centre (GC). This work will also allow to offer prospects for the first years of CTA observing the GC. By using gamma ray emission model relying on the interaction between cosmic rays and molecular clouds, and by incorporating a spatial description of the target gas, we were able to model the temporal evolution of the gamma ray flux at TeV energies from a injection spectrum of protons, a hypothesis on their diffusion speed and a particle injection scenario (2 massive flares 100 and 200 years ago). We find that the flux variations corresponding to our assumptions are of the order of 10 to 15% during the HESS observation period. With regard to the analysis of HESS data we begin with the practical application of the spectro-morphological analysis (or 3D analysis) recently developed for HESS, applied to the Galactic Center. This allows us to obtain the first intrinsic spectrum of the HESS J1745-290 source, i.e separated from any contribution from the diffuse emission. We also re-estimate of the amplitude of the systematic errors of HESS on the spectral parameters, using in particular the new numerical tools developed within the framework of the python library gammapy. The separation of the contributions from HESS J1745-290 and the diffuse emission is what allows us to better study the temporal evolution of the central source. Indeed, monitoring a source over fifteen years is made difficult by the many changes (instrumental, climatic, etc.) experienced by the HESS system. We therefore use the diffuse emission as a reference to monitor more precisely the intrinsic variations of the HESS J1745-290 source. However, we do not observe any sign of variability over the period 2004-2019. To estimate the sensitivity of HESS to temporal variations, and in order to determine the evolution scenarios that we can already exclude, we simulated HESS data, using the response functions of the instrument and different models of temporal evolution. We find that the variation in flux of HESS J1745-290 over a single year is detectable if it is greater than 30%. Then, for a linear decrease in flux between 2004-2019, HESS is able to detect it if it is greater than 30% over 16 years. We deduce that the particle injection model developed previously is not excluded by the observations of HESS. Finally, using predictive instrument functions for CTA, we were able to make predictions about CTA's performance with respect to the observation of HESS J1745-290 : we determine that CTA will have sufficient angular resolution to determine whether this gamma source is associated with Sgr A* or G359.95-0.4. In addition, CTA's sensitivity to low flux variations will confirm or invalidate the temporal evolution scenario studied in our work
Tavernier, Thomas. "Une quête de l'émission du pulsar de Vela aux hautes et très hautes énergies : observation, détection et étude, du GeV et TeV (GeV) avec le satellite Fermi et les télescopes à imagerie Tcherenkov H.E.S.S". Sorbonne Paris Cité, 2015. http://www.theses.fr/2015USPCC257.
Pełny tekst źródłaThe thesis presented in this manuscript is devoted to the study of bright pulsars shilling in -y-rays, at energies ranging from 100 MeV to several TeV. It is based on data from the LAT instrument aboard the Fermi satellite, as well as those obtained with the ground-based system of Cherenkov telescopes, H. E. S. S. , * installed in Namibia. The phased-resolved spectral measurements of pulsars with the Fermi-LAT, and in particular that of Vela (PSR B0835-45) constitutes the first step of this work. The development of an analysis method dedicated to the fifth and the largest H. E. S. S. Telescope has enabled us to detect the pulsed emission of PSR B0835-44 from ground, starting as low as 10 GeV on, and then to measure its spectrum. The very good agreement with the results obtained from the LAT data demonstrates the validity of the numerical model of the telescope and of the methodology. This is the first pulsar detected by H. E. S. S. , and the lowest energy threshold reached in Cherenkov astronomy as of today. In a third step, the analysis of data obtained on Vela with all H. E. S. S. Telescopes has resulted in an indication of a pulsed signal in the TeV range from PSR B0835-45, at a good level of confidence (4. 5 standard deviations). The spectral evaluation shows that this signal, if confirmed, represents a second component. A quick and simple study shows that this component could result from inverse Compton scattering of leptons in the pulsar wind, accelerated to ultra-relativistic energies beyond the light cylinder, on neutron star's thermal X-ray photons. These results open the perspectives for pulsar physics at tens of GeV and especially above TeV energies with the future CTA observatory
Vorobiov, Serguei͏̈. "Observations de la méthode du Crabe de 1996 à 2002 avec le télescope à effet Tcherenkov atmosphérique CAT et mise en oeuvre d'une nouvelle méthode d'analyse des gerbes atmosphériques". Palaiseau, Ecole polytechnique, 2004. http://www.theses.fr/2004EPXX0001.
Pełny tekst źródłaCzęści książek na temat "Rayons gamma aux très hautes énergies"
SOL, Hélène. "Jets relativistes et mécanismes aux très hautes énergies". W Noyaux actifs de galaxie, 165–246. ISTE Group, 2023. http://dx.doi.org/10.51926/iste.9087.ch4.
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