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Szabo, Anthony Paul. "High energy emissions for astrophysical objects." Title page, contents and abstract only, 1992. http://web4.library.adelaide.edu.au/theses/09PH/09phs996.pdf.
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Fauvet, Lauranne. "Cosmologie observationnelle avec le satellite Planck : modélisation des émissions galactiques polarisées." Phd thesis, Grenoble, 2010. http://www.theses.fr/2010GRENY032.
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Cette thése est dédiée à la mesure des anisotropies du Fond Diffus Cosmologique (CMB) ainsi qu'à la caractérisation des émissions d'avant-plan galactiques. Les travaux que nous avons réalisés s'inscrivent dans le cadre de la préparation à l'analyse des données du satellite PLANCK. Cette thèse débute par une description du modèle de Big Bang chaud et de la physique du CMB. Ensuite un état des lieux des expériences dédiées à la mesure du CMB est dressé, donnant lieu à la présentation des expériences Archeops, WMAP et PLANCK. Une deuxième partie est dédiée à la présentation des émissions galactiques diffuses puis à l'étude de ces émissions dans le plan galactique, permettant d'établir des cartes partielles des variations spatiales de la température des grains de poussière et des indices spectraux des émissions synchrotron et de poussière. Une troisième partie est dédiée à l'étude des deux principales émissions galactiques polarisées diffuses : les émissions synchrotron et de la poussière. Nous avons étudié des modèles effectifs de ces émissions basés sur l'utilisation de cartes-patron. Ensuite nous avons construit des modèles basés sur la physique de ces émissions et les avons comparés aux données Archeops et WMAP afin de contraindre les paramètres de ces modèles. Ceci nous permet de proposer pour la première fois un modèle cohérent de ces deux émissions. Ensuite nous fournissons une méthode pour améliorer ces contraintes à l'aide des données PLANCK. Dans une dernière partie nous étudions les spectres de puissance angulaires de ces émissions galactiques et estimons la contamination du signal CMB par ces émissions d'avant-plan. Enfin nous proposons une méthode pour minimiser la contamination du signal CMB de PLANCK par l'émission de la poussièreThis thesis is dedicated to the Cosmic Microwave Background (CMB) anisotropies measurement and to the characterization of the foreground Galactic emissions. This work is in the framework of the Planck satellite data analysis preparation. First, this thesis gives a description of the Big Bang model and of the CMB physics. Then, we present the Archeops, WMAP and PLANCK experiments and their data analysis. Part two is devoted to the description of the diffuse Galactic synchrotron, free-free and thermal dust emissions and to the study of those emissions in the Galactic plane. Using comparison between our simulations and the WMAP, Archeops and IRIS data we are able to provide partial maps of the spatial variations of the dust grain temperature and of the spectral index of the synchrotron and thermal dust emissions. Third part is dedicated to the study of the two main polarized Galactic emissions: synchrotron and thermal dust emissions. We evaluate effective models based on template maps. We also build physical model based on physics for these emissions that is to say shape of the Galactic magnetic field and matter density in our Galaxy. Using maps and Galactic profiles, we compare our simulations of these emissions to the Archeops and WMAP data. Thanks to that we are able to provide for the first time a coherent model of the synchrotron and thermal dust emissions. Then we propose a method to improve the constraints on our model using the PLANCK data. Finally the last part focuses on the angular power spectra of the polarized Galactic emissions. We estimate the contamination due to these foreground emissions on the CMB signal. In addition we propose a method to minimize the contamination of the CMB PLANCK data by the thermal dust emission using masks
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Jones, Laurence Richard. "X-ray emission from galactic supernova remnants." Thesis, University of Leicester, 1986. http://hdl.handle.net/2381/35703.
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X-ray emission from galactic supernova remnants X-ray images and spectra are used to determine the structure and physical conditions of shock heated interstellar gas and stellar ejecta within three galactic supernova remnants (SNRs). Parameters describing the initial supernova explosions (total energy, ejected mass) and ambient interstellar medium (density, homogeneity) are then derived. The interior density of the "middle-aged" SNR W44 is found to be fairly uniform, and inconsistent with the standard Sedov model, but similar to that predicted by models in which thermal conduction and/or heating and evaporation of engulfed, cold, interstellar clouds are important. This expanding bubble of hot, high pressure gas is likely to be an example of the formation of the hot component of interstellar medium, as detected in the vicinity of the Sun. In addition, it is likely that the SNR has collided with a nearby dense molecular cloud. The SNR W49B is found to be probably the remnant of a Type II supernova which occurred in a relatively dense medium 2000-5000 years ago. The abundance of hot iron in the ejecta is consistent with the cosmic value. The youngest SNR studied, SN1006, is found to be the remnant of a Type I supernova which occurred in a region of low, but fairly uniform (to within a factor of 2), interstellar density. Emission from reverse shocked ejecta may be most prominent in a limited area of the SNR, explaining a discrepancy between previous X-ray spectra of the remnant. A common result in all three SNRs is the detection of hot gas at their centres; the likely effects of a reverse shock and thermal conduction within SNRs are emphasized.
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Cerruti, Matteo. "High-energy emission from active galactic nuclei." Paris 7, 2012. http://www.theses.fr/2012PA077225.
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Ce manuscrit résume les travaux effectués pendant les trois années de thèse doctorale au sein du LUTh (Laboratoire Univers et Théories) et de la collaboration H. E. S. S. Le projet de recherche a été l'étude de l'émission aux hautes énergies (rayons X et rayons y) des Noyaux Actifs de Galaxies (NAG), et a comporté deux parties distinctes: d'un côté l'étude de l'émission en rayons X des galaxies de Seyfert 1 (en s'intéressant particulièrement au problème de l'excès de rayons X-mous, ou soft-excess), et d'un autre côté l'étude de l'émission en rayons y des blazars, en utilisant en particulier les données du réseau de télescopes de type Cherenkov (pour l'observation de photons aux energies de l'ordre du TeV) H. E. S. S. Après une courte Introduction sur les NAG et l'astronomie au TeV, nous décrivons tout d'abord l'émission aux rayons X des galaxies de Seyfert (Chapitre 1). Ce Chapitre est une introduction à l'étude détaillée de l'émission en rayons X de deux galaxies de Seyfert 1, Mrk 509 et Mrk 841, presentée dans le Chapitre 2. Une caractéristique importante de l'émission X de ce type de NAG est le soft-excess, qui ap- paraît comme un excès de flux au-dessous de environ 1 keV par rapport à l'extrapolation à basse énergie de la loi de puissance ajustée entre 3-10 keV. Dans ce Chapitre, nous nous concentrons en particulier sur l'interprétation de cette émission, en ajustan les données Suzaku avec trois modèles différents: une double Comptonisation, une réflexion sur la partie la plus interne du disque d'accrétion, et une absorption par un vent relativiste. Alors que pour Mrk 841 les trois scénarios donnent des résultats statistiquement équivalents, pour Mrk 509 le scénario avec reflexion est exclu. La deuxième partie commence par une introduction générale sur les blazars (Chapitre 3), avant de présenter le réseau de télescope H. E. S. S. , ainsi qu'une revue des NAG observés au TeV (Chapter 4). Nous présentons ensuite l'étude spécifique du blazar émetteur au TeV 1RXS 3101015. 9 - 311909 (Chapitre 5): l'analyse des observations effectuées par H. E. S. S. Et par d'autres observatoires dans l'optique, en rayons-X et rayons-y (ATOM, Swift et Fermi) nous permet de construire la distribution spectrale d'énergie de la source. L'émission de 1RXS 3101015. 9 - 311909 est modélisée dans le cadre d'un modèle lep- tonique, de type synchrotron self-Compton (SSC). Les Chapitres suivants sont plus théoriques, et traitent de la modélisation de l'émission des blazars. Les modèles developpés dans la littérature scientifique peuvent être divisés en deux familles: leptoniques et hadroniques, selon que les particules responsables de l'émission soient des paires electrons/positrons ou des protons, respectivement. Concernant les modèles leptoniques, nous avons developpé un nouvel algorithme numérique pour la détermination des paramètres du modèle d'émission de type SSC (Chapter 6). Cette méthode, appliquée comme exemple au cas spécifique de 1RXS 3101015. 9 - 311909, montre que, pour un blazar de type HBL (high-frequency-peaked BL Lac object), émetteur au GeV et au TeV, l'espace des paramètres du modèle SSC peut être bien determiné, et améliore les contraintes obtenues avec des formules analytiques. Nous pouvons aussi utiliser, sous certaines hypothèses, cet algorithme pour contraindre la distance d'un HBL dont on ne tonnait pas le redshift (application au cas de PKS 0447- 439). Dans le Chapitre 7 nous nous concentrons sur les processus d'émission de type hadronique, en de- crivant le développement d'un nouveau code stationnaire lepto-hadronique (qui prend en compte à la fois les processus leptonique et hadronique), et nous présentons une première application à Mrk 421 et à PKS 2155-304. Le code nous permet de modéliser l'émission des blazars dans un scenario soit lep- tonique soit hadronique, en changeant les paramètres de la région émettrice et des particules présentes. Des scenarios mixtes lepto-hadroniques (dans lesquels l'émission aux hautes énergies est associée aux deux composantes) peuvent être également étudiés dans ce contexte. Nous terminons, dans le Chapitre 8, avec la modélisation de 3C 454. 3, un blazar de type FSRQ (flat- spectrum-radio-quasar), dont le spectre au GeV est décrit par un processus de type inverse Compton sur les photons produits dans la Broad-Line-Region. Les observations conjointes du téléscope Fermi (au GeV) et des télescopes Cherenkov au sol (au TeV, comme H. E. S. S. , MAGIC, VERITAS), ont permit d'observer la composante en rayons-y des blazars avec une très bonne résolution en énergie. Le nouveau téléscope H. E. S. S. II (dont la prémière lumière a été obtenue pendant l'été 2012) va pouvoir améliorer notre connaissance des blazars, en permettant de baisser le seuil d'observation en énergie et donc d'étudier la partie du spectre compris entre Fermi et les télescopes de type Cherenkov. La communauté de l'astronomie au TeV développe actuellement le réseau de nouvelle génération, CTA (Cherenkov Telescope Array). Le projet est dans sa phase préparatoire, et !es premiers prototypes sont en construction (comme par exemple le télescope SST-GATE, sur le site de l'Observatoire de Meudon). Dans ce contexte, en appendix A est présentée une perspective de détection par CTA de blazars au grand redshift. In this thesis manuscript we tried to summarize the research work done during the last three years in the high-energy group of the LUTh laboratory, as well as in the H. E. S. S. Collaboration. The project deals with the study of high-energy emission from active galactic nuclei (AGN), where, with high energy, we refer here to X and y-rays. The thesis covers in fact two différent aspects of the physics of AGN, firstly the study of the X-ray emission from Seyfert galaxies (radio-quiet AGN), and then of the y-ray emission from blazars (radio-loud AGN). We start then by providing a short introduction to the scientific context of AGN physics (by present- ing the unified AGN model), as well as of TeV astronomy. In the first part we first describe the problem of the soft-X-ray excess in Seyfert galaxies (Chapter 1), before entering in the details of the study of Suzaku observations of two particular objects (Mrk 509 and Mrk 841, Chapter 2), presenting the data analysis and their modelling. The second part starts with an introduction on the blazar physics (Chapter 3), before showing the results achieved by the H. E. S. S. Telescope array on AGN (Chapter 4). A detailed study has been done on a particular blazar detected at TeV energies (1RXS J101015. 9 - 311909), and is presented in Chapter 5. The following chapters are more theoretical, and discuss the modelling of the observed blazar emis- sion. In particular, in Chapter 6 we discuss the constrains on the synchrotron-self-Compton model, presenting a new numerical algorithm to determine the best-fit solution, while in Chapter 7 we present a new stationary lepto-hadronic code, which can be used to model the blazar emission in leptonic, hadronic and mixed scenarios. In Chapter 8 we present the problem of the spectral break observed in the GeV spectrum of 3C 454. 3, and we model it consistently in an external-inverse-Compton scenario. Finally we present a perspective for the detection of high-redshift sources with the future telescope CTA (Appendix A)
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Espey, Brian Russell. "Emission line studies of high redshift AGN." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317876.
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Hands, Alex. "Diffuse and discrete sources of galactic X-ray emission." Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/30675.
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Our Galaxy is a luminous X-ray source by virtue of its discrete X-ray source populations and various large-scale diffuse processes which produce the ultra-hot interstellar medium. This thesis presents an analysis of the properties of a variety of Galactic X-ray emitting components, based on data from the EPIC CCD cameras onboard ESA's XMM-NEWTON satellite observatory. In total 51 individual observations are analysed for which the combined exposure time is nearly 900 ks. X-ray spectra measured over a wide range in Galactic longitude and latitude are used to disentangle the different components of the diffuse soft X-ray background (SXRB). The SXRB is comprised primarily of a two-temperature Galactic halo, an unabsorbed local hot bubble (LHB) and, in certain directions, an extended plasma 'superbubble', all with temperatures in the range of 1-3 million K. Observations towards the Galactic Plane provide evidence that the LHB may be larger in extent than has previously been assumed, with some of the emission lying behind an absorption wall with a column density of NH ~ 3 x 1020 cm-2. The diffuse hard X-ray phenomenon known as the Galactic ridge is investigated at various locations both on and near to the Galactic Plane. The spectrum of the ridge at high energies is well described by a thermal plasma model with a temperature of 108.0 K. The exact nature of this emission is uncertain but several possibilities are discussed in this thesis. The surface brightness of the ridge is measured as ~ 10-10 erg s -1 cm-2 deg-2 (2-10 keV), of which ~ 15% is due to point sources and a further ~2% has been resolved and identified as extended supernova remnants and HII regions. In the region of XMM-NEWTON's X-ray Galactic Plane Survey (XGPS), a total of 424 discrete X-ray sources have been detected. Cumulative log N - log S distributions, including data from other satellites, illustrate how the dominating source population changes from Galactic X-ray binaries at high fluxes to extragalactic objects at fainter fluxes. However, an additional lower luminosity population, possibly associated with cataclysmic variables and RS CVns, appears to contribute significantly at intermediate X-ray fluxes.
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Alves, Marta Isabel Rocha. "Diffuse radio recombination line emission on the galactic plane." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/diffuse-radio-recombination-line-emission-on-the-galactic-plane(54655adf-a0da-4f27-86fb-0d8ae43e1e80).html.
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A full-sky free-free template is increasingly important for the high-sensitivity Cosmic Microwave Background (CMB) experiments, such as Planck. On the Galactic plane, where free-free estimations from Halpha measurements become unreliable, Radio Recombination Lines (RRLs) can be used to determine the thermal brightness temperature unambiguously with no dust contamination. RRLs are a powerful tool for the diagnostic of the interstellar medium, tracing the ionised component, its electron temperature, velocity and radial distributions.This thesis describes the investigation of the ionised emission from HII regions and diffuse gas along the Galactic plane using RRLs, with the aim of providing a map of the free-free emission to complement the high latitude Halpha observations. Measuring the free-free emission on the Galactic plane is of great importance to understand and characterise other Galactic emission components: synchrotron, anomalous dust and thermal dust emission. The fully-sampled HI Parkes All-Sky Survey and associated deep Zone of Avoidance Survey are re-analysed to recover extended RRL emission. They include three RRLs (H166alpha, H167alpha and H168alpha) at frequencies near 1.4 GHz. A data cube covering l=20 degree to 44 degree and |b| < 4 degree is constructed of RRL spectra with velocity and spatial resolution of 20 km/s and 14.8 arcmin, respectively. Well-known HII regions are identified as well as the diffuse RRL emission on the Galactic plane.In order to convert the integrated RRL emission into a free-free brightness temperature a value of the electron temperature (Te) of the ionised gas is needed. Using the continuum and line data from the present survey, the variation of Te with Galactocentric radius was derived for the longitude range l=20 degree to 44 degree, with a mean Te on the Galactic plane of 6000 K. The derived Te variation was used to obtain the first direct measure of the free-free brightness in this region of the Galactic plane. Subtraction of this thermal emission from the total continuum at 1.4 GHz leaves the first direct measurement of the synchrotron emission. A narrow component of width 2 degree is identified in the synchrotron latitude distribution.Determining the free-free and synchrotron emission in this region of the Galactic plane identifies the anomalous microwave component, when combined with WMAP and IRIS data. The results are in agreement with models of small spinning dust grains.
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Mak, Wai-ying, and 麥偉瑩. "Very high energy gamma-ray emission from active galactic nuclei." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31221464.
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Mak, Wai-ying. "Very high energy gamma-ray emission from active galactic nuclei /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20567492.
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Page, Mathew James. "X-ray evolution and variability of active galactic nuclei." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267655.
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Sanguansak, Nuanwan. "A study of radio continuum emission of the Milky Way Galaxy." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5399/.
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The synchrotron emissivity distribution of the Milky Way Galaxy has been modelled from the 408 MHz allsky survey of Haslam et al.(1982) after separation of its thermal component with the help of IRAS 60 micron emission(Broadbent et al 1989). We have refined the spiral arm pattern in the inner part of the Galaxy by including a bar at the Galactic centre and an updated the Galactic distance scale and obtained fitted free parameters. At 408 MHz, there is very little absorption in the interstellar medium and the line of sight distribution of synchrotron emissivity was inferred mainly from its presumed relationship to the other tracers of spiral structure via these fitted free parameters. At lower frequencies, the absorption of synchrotron emission due to thermal electrons becomes significant and can give direct information of the nonthermal distribution along the line of sight. We have modelled the distribution of thermal electrons according to our synchrotron arm model and an alternative model based on pulsar dispersion measures using the Galactic rotation curve and the surveys of the distribution of Hl66a emission We have then used our synchrotron model applied at lower frequencies including the absorption to compare with the surveys of Dwarakanath et al.(l990) at 34.5 MHz and Jones and Finlay(l974) at 29.9 MHz. The result confirms that the absorption model of the synchrotron emissivity in the Galactic plane is broadly correct and illustrates the potentials of the absorption technique. However we were not able to distinguish the two models of ionised hydrogen spiral structure. To do this, recombination line surveys with improved frequency resolution are required. Using a new value of the cosmic ray gradient in the Galaxy from diffuse gamma-ray emission we obtain the separate variation of magnetic field and cosmic ray electron density. We give the global properties of the thermal and nonthermal emission that our model implies.
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Rowland, P. R. "Observations of the water maser emission associated with Cepheus A." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377476.
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Nenkova, Maia M. "MODELING THE INFRARED EMISSION FROM DUST IN ACTIVE GALACTIC NUCLEI." UKnowledge, 2003. http://uknowledge.uky.edu/gradschool_diss/421.
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Active Galactic Nuclei (AGN) are compact regions in the centers of some galaxies. They emit significantly in the whole range of the electromagnetic spectrum and show variability at different timescales. Observational evidence suggests the presence of a dusty torus obscuring the central radiation source of AGN. According to the Unified Model the observed general properties of AGN emission can be understood on the basis of orientation of this torus toward an observer. Two main types of AGN are distinguished: Type 1, with detected emission from the inner torus cavity viewed pole-on, and Type 2, viewed through the obscuring torus. There are numerous attempts in the past decade to model the emission from the torus, considering a homogeneous distribution of dust. However, important problems in explaining the observations still remain unsolved: it is hard to suppress the 10 m emission feature of silicate dust for a pole-on view and at the same time produce an absorption feature for an edge-on viewed torus; despite the huge optical depths inferred from X-ray observations of Type 2 sources, the observed absorption feature is shallow. Unlike observations, models of homogeneous tori with large optical depths always produce deep absorption feature. While it is realized that dust contained in clumps would resolve these issues, modeling of a clumpy medium poses a serious computational challenge. We are the first to incorporate clumps in our model of a dusty torus and to successfully explain the infrared emission from AGN. We model two types of clouds: directly illuminated by the AGN and diffusely heated by other clouds. We calculate the emission of the first type as angle-averaged emission from a dusty slab. The second type of clouds is modeled as dusty spheres embedded in the radiation field of the directly heated clouds. The radiative transfer problem for a dusty slab and externally heated sphere is solved exactly with our code DUSTY. The overall emission of the torus is found by integration over the spatial distribution of clouds. We find a very good agreement of our model results with observations. Comparison with them can constrain the physical conditions in the AGN dusty tori.
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Robinson, A. "A study of emission line variability in active galactic nuclei." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356433.
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Mannings, Vincent. "TeV gamma-ray emission from accreting binary pulsars." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6297/.
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The high-mass X-ray binary SMC X-1 has been observed during the interval 1986-1989 at a threshold γ-ray energy of 0.4 TeV using the University of Durham Mark III air Cerenkov telescope at Narrabri. The Cerenkov arrival time series recorded during these observations have been tested for periodicity at the contemporary pulse period of the SMC X-1 X-ray pulsar. This period analysis was performed using a new technique - introduced in the present work - which is designed for TeV γ-ray source candidates in binary systems and which simultaneously seeks evidence for pulsed TeV γ-ray emission and information on the location of the emission site within the binary. Results are also presented from the period analysis of data accumulated at Narrabri during observations of the low-mass X-ray binaries X0021.8-7221 (in the globular cluster 47 Tucanae) and GX 1+4. X-ray binaries as a class of TeV γ-ray source are considered and their properties compared. Previous models which invoke the interaction of beams of high-energy particles with material within the environment of a binary system are discussed. One of these models is adapted in the present work in order to propose a simple explanation of the narrow TeV 7-ray orbital light curve observed for the high-mass binary Centaurus X-3. The new model accounts for the γ-ray emission from Cen X-3 in terms of the collisions of ultrarelativistic protons with an accretion wake trailing the X-ray pulsar. This model, which incorporates the steering of charged particles in the magnetosphere of the massive primary star, is also applied to the Vela X-1 binary in order to investigate claims that TeV γ-ray outbursts observed during X-ray eclipse arise at particle collisions with the limb of the supergiant companion.
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Breedon, Lorraine Maria. "X-ray emission from low mass binary systems." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/35843.
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X-ray Emission from Low Mass Binary Systems X-ray time-series and spectra of two LMXRBs are presented. The data are from the the well-known X-ray burster MXB1636-536 and the dipping source 4U1624-49. In the case of MXB1636-536, a simultaneous optical observation is also presented. The 2-20 keV persistent X-ray emission from MXB1636-536 is found to show both positive and negative hardness-flux correlations and to vary by a factor of ∼ 2 on timescales of hours. The persistent spectrum is best described by a power law with high energy cut-off, indicative that Comptonization dominates the spectral formation in the inner accretion disk. The temperature, optical depth and Compton y parameter of the Comptonizing plasma are derived; the Compton y parameter shows that the spectrum is consistent with unsaturated Comptonization. The negative hardness-flux correlation is explained in terms of the Compton cooling of a hot neutron star corona as a result of an increase in accretion rate. It is notable that a negative hardness-flux correlation and a power law spectrum is in direct conflict with previous observations of this source. Thirteen X-ray bursts, exhibiting a wide variety of profile, were also observed from MXB1636-536. The peak burst flux and burst fluence varied by a factor of 6 and 5 respectively. The burst sample may be divided into two distinct classes: those with fast rise and high peak intensity (strong) and those with slow rise and low peak intensity (weak). Moreover, the strong bursts are 'super-Eddington' and one of the weak bursts is unusual in that it is double-peaked in both the X-ray and bolometric burst profiles. The observed burst properties are discussed within the framework of the current thermonuclear flash models and other physical scenarios. One of the bursts, observed simultaneously in both the X-ray and optical wavebands, is used to determine the possible locality of the reprocessing region in the accretion disk. 4U1624-49 reveals a pattern of dips in the 1-10 keV X-ray light-curve which repeat with a period of ~21 hours. This is almost certainly the binary period of the system, making it one of the longest binary periods amongst LMXRBs. The ∼25% residual flux can be associated with a physically extended emission component whereas the dips are associated with the intermittent obscuration of a compact component by material in the line-of-sight. The spectral changes occuring within the dips are complex and indicate energy-independent reductions in flux and substantial increases in absorption. The dips cannot be explained by a bulge at the outer disk edge (at the point of impact with the incoming stream) obscuring the central X-ray source. Assuming the primary of 4U1624-49 is a 1.4M? neutron star, the companion is likely to be an evolved star with a mass < 3M? and radius < 2.75R?. The orbital inclination is found to be within the range predicted by the FKL model for 'pure dippers' i.e. 60° < I < 75°.
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Verner, Ekaterina. "Fe II emission from H II regions and active galactic nuclei." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ49820.pdf.
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Nandra, Kirpal. "Spectral signatures in the X-ray emission from active galactic nuclei." Thesis, University of Leicester, 1991. http://hdl.handle.net/2381/35744.
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Spectral analysis of Ginga observations of Seyfert galaxies suggests a departure from the simple power law model which adequately described the HEAO-1 and EXOSAT data for these sources. In particular, compelling evidence is found for an Fe K-emission line, a K-absorption edge and a spectral flattening above about 10 keV. Analysis of a sample of AGN spectra shows that these features are extremely common. The mean energy of the emission feature suggests an origin in Fe K fluorescence from material in a low state of ionization, with a mean equivalent width ~ 150 eV. In contrast, highly ionized gas is required to reproduce the absorption edge energy. Monte Carlo modelling, carried out in various geometries, suggest that the line arises via fluorescence in cold, optically thick material out of the line of sight to the X-ray source, which is accompanied by continuum photons 'reflected' from the material. The characteristic shape of the reflected spectrum, when combined with the primary power law, leads to the observed emission line and 'hard tail'. The reflecting material must subtend a large solid angle at the X-ray source to explain the strength of the emission line and hard tail. Such a geometry is suggestive of an accretion disc. Observations of spectral variability in two Seyfert galaxies, MCG-6-30-15 and NGC 5548, show that such variability can be explained by varying proportions of directly viewed and reflected continua, constraining the extent of the reflecting material. Detailed analysis of the spectra of these two objects show that they are consistent with X-ray reflection from an accretion disc, with additional absorption by a highly ionized 'warm absorber' in the line of sight, as found for the bulk of the sample sources. In the case of NGC 5548, an extra component to the line emission from the warm absorber is also inferred. Concluding, the accretion disc reflection model provides an excellent description of the observed spectral features and variability in Seyfert galaxies, but a complex of emission lines around 6.5 keV seems highly likely. Future observations of these objects, with improved spectral resolution, should therefore be of great value.
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Jew, Luke. "Measurements of diffuse galactic emission at 5 GHz with C-BASS." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:31f0227a-84be-421a-ae46-eebe9f422767.
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The C-Band All-Sky Survey (C-BASS) is a project to produce an all-sky map in intensity and polarization at a central frequency of 5 GHz with 1 GHz bandwidth and approximately 1 degree resolution. The central frequency is low enough for the map to be dominated by synchrotron and free-free emission but high enough so that Faraday rotation and depolarization are small across most of the sky. The C-BASS map will enable a more accurate removal of contaminating foregrounds from measurements of the cosmic microwave background, particularly in polarization where the B-mode signal from inflation is likely to be orders of magnitude weaker than the diffuse Galactic foreground emission. To produce an all-sky map from the ground requires two telescopes, one in the northern and one in the southern hemisphere. This thesis focuses on analysis of C-BASS North data. The noise properties of time-ordered data are characterised by fitting a noise model to periodograms. Using simulations, the errors introduced into the C-BASS maps by a destriping mapmaker are quantified and we reduce the signal error by masking the brightest pixels during baseline offset estimation. Jackknife tests are used to test the C-BASS data for systematics and to test the accuracy of the sensitivity maps. In total intensity, the spectral index of diffuse Galactic emission between 5 GHz and 408 MHz is measured using an extended T-T plot method and the results are compared to simulations. The spectral index of polarized diffuse Galactic emission between 5 GHz and 30 GHz is estimated in 55 arcminute pixels, modelling the polarized intensity as a Rician random variable.
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Vuillaume, Thomas. "Modeling of the emission of active galactic nuclei at Fermi's era." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY089/document.
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Les noyaux actifs de galaxie (NAG) sont les objets les plus énergétiques de l'univers. Cette incroyable puissance provient de l'énergie gravitationnel de matière en rotation autour d'un trou noir super-massif siégeant au centre des galaxies. Environ 10% des NAG sont pourvus de jets relativistes émanant de l'objet central (trou noir et matière environnante) et s'étalant sur des échelles de l'ordre de la galaxie hôte. Ces jets sont observés à toutes les longueurs d'ondes, de la radio aux rayons gamma les plus énergétiques. En dépit de nombreuses études et d'instruments de plus en plus précis depuis leur découverte dans les années 1950, les NAG sont encore très mal compris et la formation, la composition et l'accélération des jets sont des questions encore pleinement ouvertes. Le modèle le plus répandu visant à reproduire l'émission des NAG, le modèle "une zone" repose souvent sur des hypothèse ad-hoc et ne parvient pas à apporter une modélisation satisfaisante.Le paradigme du "two-flow" (deux fluides) développé à l'IPAG et basé sur une idée originale de Sol et al (1989) a pour but de fournir une vision unifiée et cohérente des jets de NAG. Cette théorie repose sur une l'hypothèse principale que les jets seraient en fait composés de deux fluides co-axiaux: une colonne centrale composée d'un plasma purement leptonique (électrons/positrons) se déplaçant à des vitesses relativistes et responsable pour la grande partie de l'émission non thermique observée entourée par une enveloppe composée d'un plasma baryonique (électrons/protons), régie pas la magnéto-hydrodynamique, se déplaçant à des vitesses sous-relativistes mais transportant la majorité de l'énergie. Cette hypothèse est basée sur des indices observationnels ainsi que sur des arguments théoriques et permet d'expliquer nombre des caractéristiques des NAG.Afin d'étudier plus en profondeur le paradigme du two-flow, un modèle numérique basé sur ses concepts et produisants des observables comparables aux observations est nécessaire.Durant ma thèse, j'ai participé au développement de ce modèle, m'intéressant notamment à la diffusion Compton inverse de photons provenant de l'extérieur du jet. Ce processus, primordial dans la modélisation des NAG, est aussi central dans le paradigme du two-flow car il est à l'origine de l'accélération de la colonne via l'effet fusée Compton. Pour cela, j'ai du développer des nouvelles approximations analytiques de la diffusion Compton d'une distribution thermique de photons.En m'intéressant à l'effet fusée Compton, j'ai pu montré que dans le champ de photon thermique d'un NAG, le facteur de Lorentz d'ensemble du plasma pouvait être sujet à des variations le long du jet en fonction de la distance à l'objet central. Ces variations peuvent avoir un effet important sur l'émission observée et peuvent induire de la variabilité spatiale et temporelle. J'ai également montré que les facteurs de Lorentz terminaux obtenus étaient compatibles avec les conditions physiques attendus dans les jets et avec les observations.Le modèle complet produit des DES directement comparables aux observations. Néanmoins, le modèle est par nature erratique et il est quasiment impossible de relier directement les paramètres du modèles avec les DES produites. Malheureusement, les procédures standards d'adaptation automatique aux données (e.g. basé sur les méthodes de gradient) ne sont pas adaptées au modèle à cause de son grand nombre de paramètres, de sa non-linéarité et du temps de calcul important. Afin de palier à ce problème, j'ai développé une procédure d'adaptation automatique basée sur les algorithmes génétiques. L'utilisation de cet outil a permis la reproduction de plusieurs DES par le modèle. J'ai également montré que le modèle était capable de reproduire les DES observées avec des facteurs de Lorentz d'ensemble relativement bas, ce qui pourrait potentiellement apporter une harmonisation entre les observations et les nécessités théoriquesActive galactic nuclei (AGN) are the most energetic objects known in the universe. Their fantastic energy is due to efficient conversion of gravitational energy of mass accreted on super-massive black-holes at the center of galaxy into luminous energy. 10% of AGN are even more incredible as they display relativistic jets on galaxy scales. Those jets are observed at all energies, from far radio to highest gamma-rays. Despite intense study since their discovery in the 50's and more and more observations, favored by rapid progress in instrumentation, AGN are still widely misunderstood. The questions of formation, composition, and acceleration of jets are central but still a matter of debates. Models aiming at reproducing observed emission have been developed throughout the years. The most common one, the one-zone model, often relies on ad hoc hypothesis and does not provide a satisfactory answer.The two-flow paradigm developed at IPAG and based on an original idea from Sol et al (1989) aims at giving a more coherent and physical representation of AGN jets. The principal assumption is that jets are actually composed of two coaxial flows: an inner spine made of a pure pair plasma, moving at relativistic speed and responsible for the non-thermal observed emission surrounded by an external sheath, made of a baryonic MHD plasma, midly relativistic but carrying most of the power. The two-flow paradigm finds roots in observations as well as theoretical arguments and has been able to explain many AGN features.During my PhD, I studied this paradigm and contributed to the development of a numerical model based on its concepts. I have been particularly interested in the inverse Compton scattering of thermal photons, fundamental process in the modeling of AGN emission, as well as the Compton rocket effect, key to the acceleration of the spine in the two-flow paradigm.However, taking into account the inverse Compton emission, with the complete cross-section (including the Klein-Nishina regime) and the anisotropy can be very time consuming. To accomplish fast and efficient computation of the external Compton emission, I have had to formulate new analytical approximations of the scattering of a thermal distribution of photons.I have also studied the Compton rocket effect, responsible for the acceleration of the inner spine in the two-flow paradigm. I showed that the resulting bulk Lorentz factor of the flow in the complex photon field of an AGN is subject to variations along the jet as a function of the distance to the central engine. These variations can have drastic effects on the observed emission and could induce variability, both spatially and temporally.I also showed that the terminal bulk Lorentz factor obtained are compatible with physical conditions expected in jets and with observations.The complete model produce spectral energy distribution (SED) comparable to observed ones. However, the model is by nature erratic and it is difficult to make a direct link between the model parameters (input) and the SED (output). Unfortunately, standard data fitting procedures (e.g. based on gradient methods) are not adapted to the model due to its important number of parameters, its important computing time and its non-linearity. In order to circumvent this issue, I have developed a fitting tool based on genetic algorithms. The application of this algorithm allowed me to successfully fit several SED. In particular, I have also showed that the model, because based on a structured jet model, can reproduce observations with low bulk Lorentz factor, thus giving hope to match observations and theoretical requirements in this matter
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Johns, Bethany R. "The origin of the Galactic 511 keV positron annihilation emission morphology." Connect to this title online, 2008. http://etd.lib.clemson.edu/documents/1239894560/.
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Tamblyn, Peter. "The peculiar population of helium emission stars at the Galactic Center." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/187516.
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We show that extremely luminous, blue stars are present at the Galactic Center (GC) in numbers that are incompatible with normal stellar evolution. Helium 2.058 micrometer images with a spatial resolution of 1 arcsecond show that the helium emission is concentrated on point sources, most of which are bright in the infrared, indicating they are warm and very luminous. Comparison with Monte-Carlo stellar population models demonstrates that normal evolution is incapable of producing this population. Near-infrared spectroscopy at high angular and spectral resolutions has been obtained, along with spectra of an extensive suite of other warm, luminous stars. These spectra provide new constraints on the mass in the central 1/2 parsec and the spectral comparisons confirm the peculiarity of the GC stars. The brightest have few, if any, analogues known in the Galaxy. Constraints from space-based observations on the blue light associated with nuclear populations in nearby galaxies demonstrate that the GC is unique or in a time-dependent phase. We have examined and rejected a number of models expected to produce this density of luminous, blue stars in the central parsec. A possibility remains that they are recently formed massive stars with unusual evolution formed by close binary companions. This model predicts similar populations of peculiar stars only in other dense galactic nuclei which have undergone very recent star formation.
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Short-Long, Jessica. "CORRELATION BETWEEN EMISSION LINES AND RADIO LUMINOSITIES OF ACTIVE GALACTIC NUCLEI." UKnowledge, 2018. https://uknowledge.uky.edu/physastron_etds/55.
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Radio-loud active galactic nuclei (AGN) are one class of objects associated with accretion activity onto supermassive black holes in centers of massive galaxies. They are believed to be in a radiatively-inefficient accretion mode with low accretion rate. To understand this accretion mode, it is important to measure its radiative output at high energies (> 13.6eV), which can be traced through optical emission lines. However, little is known about their true radiative output. This is because no correlation between optical emission-line and radio luminosity has been found for the majority of low-luminosity radio AGN, which are often classified as low-excitation radio galaxies, or Fanaroff-Riley Class I (FR-I) radio galaxies. We demonstrate that most of the line emission found in these galaxies is not powered by the central AGN, but likely powered by some old stellar population. Only when this component is subtracted or otherwise taken into account can we estimate the true line emission associated with the AGN. These emissions may show interesting correlations with the radio luminosities in some cases.
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Krings, Kai Verfasser], Elisa [Akademischer Betreuer] Resconi, Jochen [Gutachter] [Greiner, and Elisa [Gutachter] Resconi. "Search for Galactic and Extra-Galactic Neutrino Emission with IceCube / Kai Krings ; Gutachter: Jochen Greiner, Elisa Resconi ; Betreuer: Elisa Resconi." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1161528865/34.
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Augustin, Ramona. "Characterising the circum-galactic medium : observations in absorption and simulations of emission." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0254.
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Comprendre les processus de flux de gaz entrant et sortant des galaxies est crucial pour les études de l’évolution des galaxies. Cependant, l’observation du médium circum-galactique (CGM) faible et diffus, où se déroulent ces processus, reste difficile. Dans ce travail, j’explore différentes méthodes pour observer, simuler et caractériser le gaz autour des galaxies dans le CGM. J'ai identifié et caractérisé des homologues de galaxie aux systèmes lorentziens (DLA) à z équivalent 1 en utilisant des observations au télescope spatial de Hubble (HS) hautement résolues spatialement. Je détermine leurs masses stellaires et constate que les galaxies sont généralement moins massives que la population moyenne des galaxies, mais suivent les tendances prédites en termes de taux de formation d'étoiles et de métallicité. La haute résolution spatiale des données optiques HST permet également de mieux regarder la morphologie de ces galaxies et de révéler des structures complexes et inattendues. Pour cartographier le CGM nous avons besoin d’observations en émission. Pour améliorer les stratégies d’observation du CGM en émission, j’ai calculé des prédictions à partir de simulations de zoom cosmologique dédiées, post-traitées avec un modèle d'émission du code CLOUDY. Cette combinaison permet de créer des cubes de données de type galaxie halo de type IFU simulés qui sont ensuite utilisés comme entrées dans les modèles d’instruments afin de préparer les observations CGM avec FIREBall-2 (spectrographe UV sur ballon) et HARMONI (IFU proche infrarouge sur l’ELT). Je trouve que FIREBall-2 est capable de détecter Ly alpha et que HARMONI est compétitif pour les études CGMUnderstanding the processes of gas flows in and out of galaxies is crucial in galaxy evolution studies. Yet, observations of the faint and diffuse Circum-Galactic Medium (CGM), where these processes take place, remain challenging. In this work, I explore different methods to observe, simulate and characterise the gas around galaxies in the CGM. I identified and characterised galaxy counterparts to Damped Lyman-alpha Absorbers (DLAs) at z equivalent 1 using highly spatially resolved Hubble Space Telescope (HST) observations. I determine their stellar masses and find that the galaxies are generally less massive than the average galaxy population, but follow the predicted trends in terms of star formation rate and metallicity. The high spatial resolution of the optical HST data also allows for a closer look at the morphology at those galaxies and reveals complex, unexpected structures. While absorption lets us investigate very faint gas, it is usually limited to a single line of sight and we need observations in emission to map the CGM and gain information on its extent and clumpiness. To improve observing strategies of the CGM in emission, I make predictions from dedicated cosmological zoom-in simulations, post-processed with a CLOUDY emission model. This combination allows to create mock IFU-like galaxy halo data cubes which are next used as input to instrument models in order to prepare CGM observations with FIREBall-2 (UV spectrograph on a balloon) and HARMONI (near-infrared IFU on the ELT). I predict that FIREBall-2 is capable of detecting Ly alpha and find HARMONI to be competitive for CGM studies
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Uchiyama, Hideki. "Study of the Galactic Diffuse X-Ray Emission with the Suzaku Satellite." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120646.
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Harper, Stuart Edward. "Single-dish intensity mapping with the QUIJOTE MFI and GBT." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/singledish-intensity-mapping-with-the-quijote-mfi-and-gbt(3bb4234f-46b7-4191-aec0-408345be1d97).html.
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Today, there are only a limited number of surveys of the sky at 1 to 20 GHz. These frequencies lie below the all-sky surveys of WMAP and Planck, but are critical in constraining the spectral slope of Galactic synchrotron emission. Knowledge of the large-scale spectral morphology of Galactic synchrotron emission is critical in the understanding of the interstellar medium and the weak signal from the polarised cosmic microwave background. Recently, ground based observations from S-PASS, C-BASS and the QUIJOTE Multifrequency Instrument (MFI) have been populating these missing frequencies. This thesis presents the first QUIJOTE MFI maps of the Northern sky in total intensity at 11, 13, 17 and 19 GHz, and the first single-dish mapping observations of Lynds dark cloud, LDN1622 at 5 and 13.7GHz. The observations from both instruments are used to probe the nature of spinning dust emission on degree and arcminute scales within the Galaxy. A full data reduction and calibration pipeline for QUIJOTE MFI time-ordered-data is described. The absolute flux density scale uncertainty of the MFI data is between 2 and 3 per cent. The pipeline characterises key properties of the MFI, such as the RFI sources, beams, bandpasses, 1/f noise and more. A key part of the pipeline was the development of an MPI ready Destriping map-maker and a maximum-likelihood map-maker. The map-making code can be applied to a range of different single-dish instruments and is used to reduce both the QUIJOTE MFI wide-survey maps of the Northern sky, and the GBT arcminute resolution raster observations of LDN 1622. A detailed discussion is given on the simulations used to test the integrity of the map-making implementation. Parametric model fitting to the SEDs of four spinning dust emission regions is performed. The MFI wide-survey maps are used in conjunction with existing multifrequency 1degree survey data. The addition of MFI maps is used to confirm the previously tentative spinning dust emission source LDN 1582/84. The mean peak frequency of spinning dust emission over the four spinning dust sources is found to be ⟨νsp⟩ = 27.2 +/- 0.7 GHz, and the mean ratio of the peak spinning dust brightness over the dust optical depth is ⟨Asp/τ250⟩ = 1.24 +/- 0.18 × 104 Jy/τ250. Spectral index maps are derived from the MFI wide-survey data in combination with 408 MHz and WMAP 23 GHz data. These maps are used to further quantify the ubiquity of spinning dust emission throughout the Galaxy. The results show that the median flux density spectral index within the inner Galactic disk for |b| < 2° is 0.24 +/- 0.07. This implies that at 23 GHz, spinning dust emission contributes 25 +/- 5 per cent of the total integrated emission within the inner disk of the Galaxy.
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Capelli, Renzo. "Diffuse Fe-Ka line emission tracing the recent history of our Galactic Centre." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-139072.
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Mullaney, J. R. "The location and kinematics of the emission line regions in active galactic nuclei." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/2250/.
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This thesis contains the results from a study of the optical emission lines of various samples of active galactic nuclei (AGN). We have used three separate techniques to determine the precise kinematics and the relative location of the emission line regions of AGN: a detailed study of a small sample (10) of AGN, a study of the general emission line properties of two larger samples, and the interpretation of the results from observations using numeric photoionisation models. Although we present results on both the broad line and narrow line regions of AGN the main drive behind this work is the study of the poorly defined intermediate line region using emission from highly ionised species (high ionisation emission lines). Our results derived from observations indicate that a significant proportion of the emission from these species is produced within the central void of the putative dusty torus and that emission from more highly ionised species increases at radii closer to the central engine of the AGN. Furthermore, we find strong evidence that the intermediate region traced by these high ionisation emission lines is generally outflowing from the central engine but there is little evidence of any significant acceleration or deceleration of this material between the inner and outer regions traced by the higher and lower ionisation lines, respectively. Our results derived from numerical photoionisation codes support a model in which this outflowing material responsible for the high ionisation line emission is launched from the inner edge of the the dusty torus.
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Kelley-Hoskins, Nathan. "A Search for Extended Gamma-Ray Emission from the Galactic Center with VERITAS." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21307.
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Dunkle Materie bindet etwa 24 % der gesamten Energie im Universum. Bis heute ist jedoch dessen Ursprung nicht bekannt. Untersuchungen von Galaxien und kosmologischen Messungen deuten auf Dunkle Materie hin. Ein Kandidat für Dunkle Materie ist das sogenannte Weakly Interactive Massive Particle (WIMP), welches nur der Schwerkraft und der schwachen Wechselwirkung unterliegt. Eines dieser supersymmetrischen Teilchen ist das Neutralino. Das Ziel dieser Arbeit ist es, nach Dunkler Materie in dieser Form zu suchen.
Aufgrund seiner Nähe sowie der hohen Dichte an Dunkler Materie bietet das Zentrum unserer Galaxie besondere Möglichkeiten zur Suche nach diesen Teilchen. Es wird vermutet, dass Neutralinos miteinander wechselwirken, dabei in Teilchen des Standard Modells zerfallen und so Photonen mit hohen Energien entstehen. Die Suche nach hochenergetischen Gammastrahlen in der Nähe des Galaktischen Zentrums kann folglich das Rätsel der Dunklen Materie lösen.
Das Gammastrahlenobservatorium VERITAS hat das Galaktische Zentrum für etwa 108 Stunden beobachtet. Diese Daten wurden mittels einer unbinned Likelihood-Analyse auf die Existenz von Dunkler Materie untersucht. Da VERITAS das Galaktische Zentrum bei geringer Elevation beobachtet, können nur Gammastrahlen in einem Energiebereich zwischen 4 und 70 TeV detektiert werden. Die Analysemethode modelliert sowohl die räumliche Verteilung der Dunklen Materie als auch das Gammastrahlenspektrum. Der Beitrag der Gammastrahlen, welcher nicht von Dunkler Materie erzeugt wird, ist mittels einer punktförmigen Quelle modelliert. Zum Schluss wird der Untergrund mit realen Daten außerhalb des Galaktischen Zentrums abgeschätzt.
Im Energiebereich zwischen 4 und 100 TeV wurden keine Signale der Dunklen Materie gefunden. Obere Grenzwerte für den Wechselwirkungsquerschnitt der WIMPs ergeben ⟨σv⟩ < (6.6 − 7.6) × 10−25 cm^3 oberhalb von 70 TeV in einem 95-prozentigen Erwartungsintervall.Dark matter accounts for 24% of the universe’s energy, but the form in which it is stored is currently unknown. Understanding what form this matter takes is one of the major unsolved mysteries of modern physics. Much evidence exists for dark matter in the measurements of galaxies, dwarf galaxies, galaxy clusters, and cosmological measurements. One theory posits dark matter is a new undiscovered particle that only interacts via gravity and the weak force, called a weakly interacting massive particle (WIMP). One WIMP candidate is a supersymmetric particle called a neutralino. The objective of this thesis is to search for these dark matter particles, and attempt to measure their mass and cross section. Dark matter particles appear to concentrate in most galaxy-scale gravitational wells. One region of space that is both nearby and assumed to have a high density of dark matter is the center of our own galaxy. The neutralino is expected to annihilate into Standard Model particles, which may decay into photons. Therefore, a search for gamma rays near the Galactic Center may uncover the presence of dark matter. 108 hours of VERITAS gamma-ray observations of the Galactic Center are used in an unbinned likelihood analysis to search for dark matter. The Galactic Center’s low elevation results in VERITAS observing gamma rays in the 4–70 TeV energy range. The analysis used in this thesis consists of modeling the halo of dark matter at the Galactic Center, as well as the spectrum of gamma rays produced when two WIMPs annihilate. A point source is added to model the non-dark-matter gamma-ray emission detected from the Galactic Center. Background models are constructed from data of separate off-Galactic-Center observations. No dark matter signal is found in the 4–100 TeV mass range. Upper limits on the WIMP’s velocity-averaged cross section have been calculated, which above 70 TeV result in new limits of ⟨σv⟩ < (6.6 − 7.6) × 10−25 cm3 at the 95% confidence level.
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Cota, Stephen A. "The astrophysics of nebulae and active galactic nuclear emission-line regions : new methods and applications /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487331541707918.
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Wong, Yuen-lam. "Transient radiation emission from astrophysical jets." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39378512.
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Wong, Yuen-lam, and 黃菀林. "Transient radiation emission from astrophysical jets." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39378512.
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Dudik, Rachel. "Low ionization nuclear emission line regions : the 'missing link' in the active galactic nucleus population." Fairfax, VA : George Mason University, 2007. http://hdl.handle.net/1920/2882.
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Thesis (Ph. D.)--George Mason University, 2007.Title from PDF t.p. (viewed Jan. 17, 2008). Thesis director: Shobita Satyapal. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physical Sciences. Vita: p. 217. Includes bibliographical references (p. 202-216). Also available in print.
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Walton, Dominic James. "X-ray emission and reflection from accreting black holes." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610596.
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Worsley, Matthew Alexander. "Absorbed emission from active galactic nuclei and the resolution of the x-ray background." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615313.
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Quiret, Samuel. "Circum galactic medium emission : from modeling to detection by a dedicated UV space mission." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4735/document.
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L’évolution des galaxies est un sujet relativement débattu en astronomie extra-galactique, étant donné que la plupart des mécanismes responsables des propriétés observées dans les galaxies (masse, taux de formation d’étoiles, contenu en métaux, moment angulaire) sont encore peu contraints et certains ne sont probablement même pas encore observés. Ma thèse porte sur une analyse de la région entourant les galaxies, connue sous le nom de Milieu Circum Galactique (MCG). Le MCG est à l’interface entreles galaxies et le Milieu Inter Galactique (MIG) et est considéré comme le lieu de prédilection pour les échanges gazeux et énergétiques entre les galaxies et le MIG, ce qui en fait la clé pour une meilleure compréhension de l’évolution des galaxies et du destin des baryons. Je présenterai dans un premier temps l’analyse d’un échantillon de systèmes à forte absorption issuent de la spectroscopie de quasars en absorption qui tracent les régions denses en hydrogène généralement associées au MCG des galaxies.Dans un deuxième temps, je présenterai ma contribution au développement d’une mission ballon embarquant un spectrographe UV, FIREBall-2, spécialement conçu pour observer l’émission faible et diffuse du MCG des galaxies à décalage vers le rouge inférieur à 1. D’un point de vue technique, je présenterai l’étude du composant optique clé de l’instrument: le réseau. D’un point de vue modélisation, je décrirai une simulation complète des observations, qui servira à la préparation du vol prévu pour l’Automne 2017notamment en ce qui concerne la sélection des cibles, la stratégie observationelle et le traitement des donnéesThe evolution of galaxies is a rather hot topic in extra galactic astronomy, as many of the main mechanisms underlying the observed properties of galaxies (mass, star formation rate, metal content, angular momentum) are still poorly constraints and many of them are probably undiscovered yet. My thesis focuses on an analysis of the region surrounding galaxies, known as the Circum Galactic Medium (CGM). The CGMinterfaces the galaxy with the Inter Galactic Medium (IGM) and is thought to be the most active location for gas and energy exchanges (in and out), which makes it a key ingredient towards a better understanding of galaxy evolution and the fate of all baryons. I will present in a first part, the analysis of a sample of strong absorption features based on quasar absorption spectroscopy, that probe the dense neutral hydrogen usually associated with galaxies’ CGM. In a second part, I will present my contribution to the development of a balloon-borne UV spectrograph, FIREBall-2, specifically designed to observe the faint and diffuse emissions from the CGM of galaxies at redshifts below 1. On the technical side, I will present the characterization of the key optical component ofthe instrument: the grating. On the modeling side, I will focus on an end-to-end pixel simulation of the observations to prepare for the upcoming flight, planned for Autumn 2017, in terms of target selection, observational strategy and data analysis
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Lambert, Alyn. "Gamma-ray emission above 10sup(15)eV from Cygnus X-3 and other galactic sources." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371051.
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Balenderan, Shangkari. "On the connection between the γ-ray and (sub-)mm emission in active galactic nuclei." Thesis, Durham University, 2016. http://etheses.dur.ac.uk/11934/.
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This research investigates the connection between the submillimetre (sub-mm), millimetre (mm) and gamma-ray emission in a sample eight blazars (consisting of high- and intermediate-frequency peaked BL Lacertae Objects (HBLs and IBLs respectively) as well as Flat Spectrum Radio Quasars (FSRQs)) and one radio galaxy. Light curves using both short-term (~6 days to ~3 months) and long-term (5.5 - 12 years) observations at gamma-ray and (sub-)mm wavebands are presented. Long-term light curves at (sub-)mm wavelengths show evidence that emission at these wavelengths is source class dependent. Similarities in emission patterns and flux variability were observed between FSRQs and IBLs. The correlation between emission at 1.35 mm and the 100 MeV to 100 GeV gamma-ray wavebands was studied both qualitatively and statistically using the discrete correlation function (DCF) method. Results from the DCF analysis showed that while all sources exhibit different behavioural patterns at different epochs, some general trends can be drawn based on the source type. It was found that IBLs behaved more like FSRQs than HBLs, although IBLs are classified as BL Lacertae objects, with HBLs showing the weakest correlation and variability at both emission bands and FSRQs showing the strongest evidence for correlation and variability within this sample set. This provides further evidence for the hypothesis of the unified Active Galactic Nuclei model, in which these objects evolve from FSRQ type blazars into IBLs and then into HBLs. This is because IBLs exhibit behavioural patterns of both FSRQs and BL Lacertae objects. In addition to this, time delay analysis of 3C 454.3, BL Lacertae and 3C 273 in the correlation study yielded separation distances between the emission regions ranging between ~0.1 pc to ~19 pc in the rest frame of the observer. These are in agreement with other studies in the literature (e.g. (214;42)). However, much greater separation distances were observed for 3C 279 and OJ 287 (> 70 pc). These findings suggest that the nature and geometry of blazar jets are highly complex and vary from epoch to epoch. It was concluded that extensive consistent long-term multiwavelength studies of a larger sample of sources from all blazar sub-classes would help further constrain the location of the wavelength-dependent emission regions in the jet.
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Savić, Đorđe. "Measuring black hole masses in active galactic nuclei using the polarization of broad emission lines." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE034.
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Les trous noirs supermassifs (SMBH) se trouvent au coeur de presque toutes les galaxies massives dans l’Univers. La plupart sont en sommeil, mais lorsqu’il y a assez de gaz à proximité, ils entrent dans une phase active et forment ce qu’on appelle un noyau actif de galaxie (AGN). Ils ont alors un effet profond sur l'évolution de la galaxie hôte et jouent un rôle important sur leur environnement. La mesure fiable de la masse des SMBH est donc une tâche importante dans l'astronomie moderne. À cette fin, Afanasiev et Popovic (2015) ont récemment proposé une méthode qui utilise la rotation de l'angle de position du plan de polarisation sur le profil en fréquence des raies d'émission larges afin de tracer le mouvement Keplerien et de déterminer la masse du SMBH. Le but de la thèse est d'explorer théoriquement les possibilités de cette méthode. Pour ce faire, nous avons dans une première partie effectué de nombreuses simulations de transfert radiatif pour la modélisation de la diffusion équatoriale dans AGN à l'aide du code STOKES. Nous avons inclus les mouvements complexes présents dans le système sous forme d’accrétion et d’éjection, et nous avons également comparé nos résultats aux observations. Notre travail est important car nous avons démontré dans quelles circonstances cette méthode peut être utilisée pour mesurer la masse du trou noir de manière indépendante. La deuxième partie de ce travail consiste à prédire la polarisation des raies larges au cas où les AGN seraient alimentés par des trous noirs binaires supermassifs (SMBBH). Nous avons traité quatre cas différents avec des binaires de trous noirs séparés de moins d’un parsec, et modélisé à nouveau la diffusion équatoriale. Nous avons obtenu une signature de polarisation unique sur les raies larges. Nous avons montré que la spectropolarimétrie pouvait constituer un outil puissant et une première étape pour la recherche de SMBBH dans les futurs levés spectropolarimétriques systématiquesSupermassive black holes (SMBHs) reside in the heart of nearly every massive galaxy in the Universe. Most of them lie dormant, but when the nearby gas is abundant, it will enter an active phase and form an active galactic nucleus (AGN). When in their active phase, SMBHs have a profound effect on the host galaxy evolution and play an important role in shaping their environment. Reliable SMBH mass measuring is therefore an important task in modern astronomy. For that purpose, a method has been recently proposed by Afanasiev & Popovic (2015) that uses the rotation of the polarization plane position angle across the broad emission line profile in order to trace the Keplerian motion and determine the SMBH mass. The goal of the thesis is to theoretically explore the possibilities of this method. In order to do that, we performed numerous radiative transfer simulations for modeling equatorial scattering in AGNs using the code STOKES. We included complex motions present in the system in the form of inflows and outflows, and we also compared our results with observations. We have demonstrated under which circumstances this method can be used to measure the SMBH mass in a new independent way. The second part of this work involves predicting the broad lines polarization when AGNs are powered by supermassive binary black holes (SMBBHs). We treated four different cases with sub-pc SMBBHs, and again modeled equatorial scattering. We obtained a unique polarization signature across the broad lines. We have shown that spectropolarimetry could be a powerful tool and a first step for searching SMBBHs in the future systematic spectropolarimetric surveys
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Irfan, Melis Omer. "The C-Band All Sky Survey (C-BASS) : observing diffuse Galactic emission at 5 GHz." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/the-cband-all-sky-survey-cbassobserving-diffuse-galactic-emission-at-5-ghz(cba1c8ba-6aca-4777-8a2f-d94cc4ea4eeb).html.
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Measurements of the diffuse Galactic emission are used for both the interpretation of sensitive cosmic microwave background data and the understanding of our Galaxy. I examine the diffuse Galactic emission at a central frequency of 4.76 GHz using data from the C-Band All-Sky Survey (C-BASS). The technical work presented here fo- cuses on microphonic oscillation mitigation, receiver noise measurements and radio frequency interference detection. Northern C-BASS is a continuous comparison ra- diometer with a system temperature of 40 K, a knee frequency of 0.10 mHz in polari- sation and a noise level of 2 mK sqrt(s). A calibration scheme was devised, using astro- nomical calibrators, to convert the data to Kelvin and correct for atmospheric opacity. This scheme is stable to 1 % over several months and accurate to better than 5 %. A major systematic in the C-BASS data is ground emission. In this work the ground emission is modelled and subtracted from the data resulting. A first scientific anal- ysis of C-BASS Northern intensity data was made to investigate the contributions of free-free and synchrotron emission within the Galactic plane. The synchrotron spectral index was determined to be −2.63±0.07 between 0.408 and 4.76 GHz and −2.71±0.14 between 1.420 and 4.76 GHz and the ratio of free-free to synchrotron emission at 4.76 GHz was found to be 53± 8 % to 47± 8 %. Bringing in higher frequency data allowed for the detection of anomalous microwave emission associated with W43, W44 and W47 at a level of 4.9σ, 6.0σ and 3.4σ, respectively and demonstrated the need for C-BASS data to constrain the spectral form of AME within certain regions.
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Nobukawa, Masayoshi. "Study of X-ray Emission from the Giant Molecular Clouds in the Galactic Center Region." 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/142375.
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Perna, Michele <1987>. "Starbursting to Quenching: the Role of X-Ray Emission in Active Galactic Nuclei Feedback Processes." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7767/1/perna_michele_tesi.pdf.
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One of the most debated topics of modern extragalactic astrophysics is the co-evolution between the SMBHs sitting in the nuclei of the galaxies and their hosts.
According to the most popular models of AGN and galaxies co-evolution,
starburst galaxies, unobscured quasars and inactive (and quenched) galaxies represent the different phases of an evolutionary sequence reproducing the most massive galaxies observed in the Universe. In this context, gas flows in the form of energetic outflows are postulated to play a pivotal role in this process, given that they regulate both accretion and ejection of material onto and from the SMBH, acting on the fuel from which new stars form and stopping the host galaxy growth.
In order to validate this AGN-galaxy binding nature, we investigate the kinematic and physical properties of ionized and atomic gas components of the ISM of well selected AGN-galaxy systems, obtained from ultraviolet, optical, near-infrared spectroscopic analysis, to unveil the presence of outflows. In particular, we propose and test different selection criteria to isolate sources at z ~2 in the predicted feedback phase, starting from multiwavelength information collected in the COSMOS field. As a complementary approach, we also collect a large sample of X-ray selected AGNs at z < 0.8 from the SDSS database to unveil the incidence of outflows and prove the crucial role of X-ray observations for the investigation of the feedback phase.
We combine the ionized/neutral gas kinematic and physical conditions with SMBH accretion and host galaxy properties, recovered from multiwavelength spectral energy distribution analysis and X-ray spectroscopic investigation, to infer the general conditions regulating the feedback processes. We also discuss our results in the context of the more recent observational and theoretical clues.
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Feltre, Anna. "Multi-band Emission of Active Galactic Nuclei: the Relationship of Stellar and Gravitational-Accretion Activity." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3423457.
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One of the remaining open issues in the context of the analysis of active galactic nuclei is the evidence that nuclear gravitational accretion is often accompanied by a concurrent starburst activity. What is, in this picture, the role played by the obscuring dust around the nucleus and what does the state of the art models have to say? Can the infrared data provided by Spitzer and Herschel help us in extensively investigate both phenomena and, if so, how and with what limitations? Does the presence of an active nucleus have an impact in the mid- and far-infrared properties of galaxies? Which are the effects of simultaneous nuclear gravitational accretion and starburst activities in these same galaxies?
This Thesis presents our contribution to the efforts of answering these questions. I report on results coming from a comparative study of various approaches adopted while modelling active galactic nuclei, focusing mostly on the much-debated issue about the morphology of the dust distribution in the toroidal structure surrounding their nuclear centre. We largely illustrate that properties of dust in active galactic nuclei as measured by matching observations (be it broad band infrared photometry or infrared spectra) with models strongly depend on the choice of the dust distribution.
Further, I describe a spectral energy distribution fitting tool appositely developed to derive simultaneously the physical properties of active nuclei and coexisting starbursts. The procedure was developed to make the best use of Spitzer and Herschel mid- and far-infrared observations. Such data play a crucial role in this context, providing much stronger constraints on the models with respect to the previous observing facilities. The tool has been applied to a large sample of extragalactic sources representing the Herschel/Multi-tiered Extragalactic Survey population with mid-infrared spectra from Spitzer and with a plethora of multi-wavelength data (SDSS, Spitzer and Herschel/SPIRE). The goal of such work is to study the impact of a possible presence of an active nucleus on the host galaxy's properties. Finally, I present the main results obtained. In particular, I focus on the analysis of the star formation rate in connection to the presence of an active nucleus and on the
comparison of the properties of the hot, heated by the active nucleus, and cold, starburst heated, dust components.Una delle questioni ancora aperte nell'ambito dell'analisi dei nuclei galattici attivi riguarda il fatto che l'accrescimento gravitazionale nucleare è spesso accompagnato da una concomitante attività di formazione stellare . Qual è, in questo contesto, il ruolo assunto dalla polvere oscurante che circonda il nucleo e cosa può dirci lo stato dell'arte dei modelli a riguardo? Riescono i dati infrarossi dei satelliti Spitzer e Herschel a permettere uno studio approfondito di entrambi i fenomeni e, in tal caso, come e con quali limitazioni? La presenza di un nucleo attivo ha effettivamente un impatto sulle proprietà medio e lontano infrarosse delle galassie ospiti? Quali sono gli effetti della simultaneità dell'accrescimento gravitazionale nella regione nucleare e dell'attività di formazione stellare in queste stesse galassie? In questa Tesi viene esposto il nostro contributo al tentativo di rispondere a queste domande. Vengono presentati i risultati di uno studio comparativo tra diversi approcci usati per modellare i nuclei galattici attivi, focalizzandosi soprattutto sulla questione, attualmente ancora molto dibattuta, relativa alla morfologia della distribuzione della polvere nella struttura toroidale che circonda il centro del nucleo. Viene mostrato in maniera esaustiva che le proprietà della polvere dei nuclei attivi, ottenute dal confronto tra modelli e osservazioni (sia fotometria infrarossa a banda larga che spettro medio infrarosso), dipendono fortemente dalle assunzioni sulla distribuzione della polvere. Viene fornita, inoltre, una descrizione dettagliata della tecnica di sintesi spettrofotometrica sviluppata allo scopo di ricavare contemporaneamente le proprietà fisiche dei nuclei attivi a delle coesistenti galassie ''starburst''. Tale procedura è stata sviluppata per sfruttare al meglio le osservazioni medio e lontano infrarosse dei satelliti Spitzer e Herschel. In questo contesto, tali dati giocano un ruolo cruciale fornendo vincoli molto più forti sui modelli rispetto alle precedenti strutture osservative. Il codice di sintesi spettrofotometrica è stato usato su un vasto campione di sorgenti extragalattiche rappresentanti la popolazione della Herschel/Multi-tiered Extragalactic Survey per le quali erano disponibili sia lo spettro medio infrarosso di Spitzer che un pletora di dati multi-banda (SDSS, Spitzer e Herschel/SPIRE). L'obiettivo di tale lavoro è quello di studiare l'impatto che l'eventuale presenza di un nucleo attivo potrebbe avere sulle proprietà delle galassie ospiti. Infine, vengono presentati i principali risultati ottenuti, con particolare attenzione all'analisi del tasso di formazione stellare in relazione alla presenza di un nucleo attivo e al confronto delle proprietà della polvere calda, riscaldata dal nucleo attivo stesso, e fredda, riscaldata dalla formazione stellare.
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Arrieta, Lobo Maialen. "A study of the emission processes of two different types of gamma-emitting Active Galactic Nuclei." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLE0010/document.
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Ce manuscrit de thèse présente l’étude des processus d’émission de deux types de noyaux actifs de galaxie détectés aux rayons gamma : des blazars vues au TeV et des Narrow Line Seyfert 1s (NLS1s) détectés au GeV. La distribution spectrale d’énergie des blazars peut être décrite en général par des modèles 'one-zone synchrotron self-Compton'. Ce modèle a été appliqué au blazar 1ES2322-409 qui fut premièrement détecté au TeV par l’expérience HESS. Des composantes externes comme le tore, le disque d’accrétion, la couronne X ou la 'Broad Line Region' sont nécessaires pour expliquer la radiation observée dans des NLS1 qui émettent des rayons gamma. Un modèle numérique qui considère ces champs des photons externes a été développé. Ce modèle explique l’émission observée et la transition entre des états bas et des états d’émission augmentée pour trois NLS1s vues au régime gamma : 1H0323+342, B20954+25A et PMN J0948+0022This thesis manuscript presents the study of the emission processes of two types of gamma-emitting active galactic nuclei: TeV-detected blazars and GeV-detected Narrow Line Seyfert 1s (NLS1s).The Spectral Energy Distribution (SED) of TeV blazars can in general be well described by simple one-zone synchrotron self-Compton models. Such model has been applied to the blazar 1ES2322-409 that was first detected at TeV by the HESS collaboration.Additional external photon fields such as the obscuring torus, the accretion disc, the X-ray corona or the broad line region are necessary to describe the observed radiation and broad-band SED of gamma-emitting NLS1s. A numerical model that takes into account emission from these external fields has been developed. The model explains the observed emission and the transition from quiescent to gamma-ray flaring states of three gamma-emitting NLS1s: 1H0323+342, B20954+25A and PMN J0948+0022
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Constantin, Anca. "Linking the Power Sources of Emission-Line Galaxy Nuclei from the Highest to the Lowest Redshifts." Ohio University / OhioLINK, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1097611827.
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Fields, Dale L. "Absorption-line measurements of AGN outflows." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1155913695.
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Capelli, Renzo [Verfasser], and Werner [Akademischer Betreuer] Becker. "Diffuse Fe-Kα line emission tracing the recent history of our Galactic Centre / Renzo Capelli. Betreuer: Werner Becker." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2011. http://d-nb.info/1019479191/34.
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Nobukawa(Kawabata), Kumiko. "X-ray Study of Neutral Iron Line Emission in the Galactic Ridge: Contribution of Low-Energy Cosmic Rays." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215310.
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Fukumura, Keigo. "Relativistic Accretion Flows onto Supermassive Black Holes: Shock Formation and Iron Fluorescent Emission Lines in Active Galactic Nuclei." Thesis, Montana State University, 2005. http://etd.lib.montana.edu/etd/2005/fukumura/FukumuraK0505.pdf.
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One of the exciting discoveries from the recent X-ray spectroscopic studies of active galactic nuclei (AGNs) is the so called "relativistically-broadened iron fluorescent emission line" often detected in the hard X-ray spectra. It is generally believed to originate from the inner part of the accretion disk surrounding a supermassive black hole (BH) at the center. Although we have begun to obtain some physical insight regarding such emission lines supported by theoretical models (e.g., disk-corona model), exactly how and where the observed fluorescence may take place is still disputable. Here, an X-ray data with XMM-Newton Observatory of a typical narrow-line Seyfert 1 galaxy, NGC 4051, is analyzed based on a partial covering model to consistently explain the observed time-resolved temporal/spectral variations. This model implies that the intrinsic emission varies significantly in the presence of the covering cloud. We often detect a hard X-ray continuum originating from a hot region close to the central engines of AGNs. As a promising X-ray source candidate, relativistic hydrodynamic (HD) shocks are investigated systematically and then extended to the magnetohydrodynamic (MHD) shocks, given the widely accepted suggestion that the presence of the magnetic fields could play an important role in the accreting flows. I show that both HD and MHD shocks can form in the vicinity of the BH, perhaps responsible for creating such a high temperature region where hard X-rays are produced. Particularly in the MHD shocked plasma, the hydro/magneto-dominated states are found. Considering the effect of such magnetic fields in the accretion disk, I calculate nonstandard iron fluorescent line profiles in the presence of spiral density waves and find multiple sharp sub-peak structures in extremely skewed line profiles, which will be detectable with upcoming X-ray satellites such as Astro-E2 XRS for testing the model. This dissertation is the result of my own work and also includes some work done in collaboration. Parts of this dissertation have been either already published in or submitted to the Astrophysical Journal and presented at conferences, while some are still in progress.