Dissertations / Theses on the topic 'Nucleon and gamma ray emission'

The detection of γ-rays from explosive astrophysical scenarios such as novae provides an excellent opportunity for the study of on-going nucleosynthesis in the Universe. Within this context, this work has addressed an uncertainty in the destruction rate of the 18F nucleus, thought to be the primary source of 511 keV γ-rays from novae. A direct measurement of the 18F(p,α )15O cross section has provided the opportunity to extract resonance parameters through the R-Matrix formalism. The inferred parameters of populated states in 19Ne include the observation of a broad 1/2+ state, consistent with a recent theoretical prediction, which will have a significant impact on the rate of destruction of this γ-ray producing radioisotope. The 18O(p,α )15N reaction follows similar nuclear and kinematic processes and is expected to occur in the hydrogen burning layers of AGB stars. Resonance widths have been extracted from a direct measurement in the region around a poorly constrained broad state close to the Gamow window. This has produced a new parameter set for future reference and provides new information on the reaction rate. The complex R-Matrix formalism used in these analyses is a crucial tool in the study of nuclear astrophysics reactions, and many codes have been written to implement the complex mathematics. This thesis presents a comparison of two publicly available codes from the JINA collaboration and a code used extensively by the University of Edinburgh. For this, the recent results of the 18F destruction reaction, presented here, have been used. A minor error was found within one of the codes, and corrected. The final parameters extracted, and the resulting cross sections calculations, are shown to be consistent between the three codes. A further γ-ray line of interest at 1.809 MeV, characteristic of 26Al decay, has been observed throughout the interstellar medium. If, however, this isotope is formed in a known isomeric state, its decay bypasses the emission of this γ-ray, thus complicating the interpretation of observed γ-ray fluxes. To this end, an experiment has been carried out, providing proof of principle of a direct measurement of the 26mAl(p,γ)27Si reaction. The calculation of the isomeric intensity is presented here.

Angetrieben durch die Akkretion von Materie in ein super massives Schwarzes Loch in ihrem Zentrum, stellen aktive Galaxien die stärksten und beständigsten Strahlungsquellen im Universum dar. Ihre elektromagnetische Emission kann sich bis in den Gammastrahlenbereich ausbreiten. Das Ziel dieser Arbeit ist, diese Mechanismen und die Orte jenseits der hoch energetischen Emission zu charakterisieren. Dafür werden die Observationen von zwei Aktiven Galaxien im Bereich von hunderten von GeV verwendet, welche mit den Cherenkov Teleskopen MAGIC aufgenommen wurden. Die physikalische Interpretation wird durch Beobachtungen mit dem Fermi Gamma-ray Space Teleskop und durch Multiwellenlängendaten unterstützt. Es werden zwei Aktive Galaxien mit Jet untersucht: PKS 1510-089 und NGC 1275. Die MAGIC Teleskope, welche PKS 1510-089 seit 2012 immer wieder beobachten, detektieren eine signifikante Emission über dutzende von Observationsstunden, was auf schwache aber kontinuierliche Gammastrahlung aus dieser Quelle hinweist. NGC 1275 zeigte in der Periode von September 2016 bis Februar 2017 einen großen Ausbruch im Gammerstrahlenbereich: MAGIC zeichnete eine Variabilität in der Größenordnung von wenigen Stunden und die erstmalige Emission von TeV Photonen. Aus beiden untersuchten Quellen ist ersichtlich, dass die Kombination von Daten aus verschiedenen Instrumenten die physische Diskussion entscheidend beeinflusst. Der Übergang zu zugänglichen und interoperablen Daten wird zu einem zwingenden Thema für Gammastrahlenastronomen, und diese Arbeit stellt das technische Bestreben dar, standardisierte hochrangige Daten für Gammastrahleninstrumente zu erzeugen. Ein Beispiel für eine zukünftige Analyse, die einheitliche High-Level-Daten von einem Gammastrahlensatelliten und vier Cherenkov-Teleskopen kombiniert, wird vorgestellt. Der neue Ansatz, der vorgeschlagen wird, führt die Datenanalyse durch und verbreitet die Ergebnisse, wobei nur Open-Source-Ressourcen verwendet werden.
Powered by the accretion of matter to a supermassive black hole, active galactic nuclei constitute the most powerful and persistent sources of radiation in the universe, with emission extending in the gamma-ray domain. The aim of this work is to characterise the mechanisms and sites beyond this highly-energetic radiation employing observations of two galaxies at hundreds of GeV, conducted with the MAGIC imaging Cherenkov telescopes. The physical interpretation is supported with observations by the Fermi Gamma-ray Space Telescope and with multi-wavelength data. Two peculiar jetted galaxies are studied: PKS 1510-089 and NGC 1275. The first source, monitored by MAGIC since 2012, presents a significant emission over tens of observation hours, in what appears to be a low but persistent gamma-ray state. The second source has instead shown, in the period between September 2016 and February 2017, a major outburst in its gamma-ray activity with variability of the order of few hours and emission of TeV photons. The broad band emission of jetted galaxies is commonly modelled with the radiative processes of a population of electrons accelerated in the jet. While PKS 1510-089 conforms to this scenario, modelling the gamma-ray outburst of NGC 1275 requires placing the acceleration and radiation of electrons close to the event horizon of the black hole. From both the sources studied it is evident that the combination of data from different instruments critically drives the physical discussuion. Moving towards accessible and interoperable data becomes a compelling issue for gamma-ray astronomers and this thesis presents the technical endeavour to produce standardised high-level data for gamma-ray instruments. An example of a future analysis combining uniformed high-level data from a gamma-ray satellite and four Cherenkov telescopes is presented. The novel approach proposed performs the data analysis and disseminates the results making use only of open-source assets.

The distribution of 75Se in tissue equivalent materials was investigated employing Gamma ray Emission Tomography with a rectilinear scanner utilizing NaI(Tl) and BGO detectors. The reconstructed images, using Filtered Back Projection and Iterative techniques were presented in 2D colour and 3D representations. Using a lead collimator of aperture 1.5x20 mm and 70 length, the distribution of selenium with variation of volume and concentration was examined and clearly seen. Several corrections such as background, scattering, attenuation compensation and X-ray characteristic suppression, were performed to improve the quality of the images which was evaluated in terms of the fidelity factor. The possibility of quantifying an image was considered with regard to spatial resolution and least detectable concentration. The spatial resolution was measured using two small vials containing the same concentration of selenium, the value obtained was the same as the width of the collimator aperture. The value of the least detectable concentration of selenium however, was difficult to find, due to the many ambiguous factors involved. The binding site of selenium which is based on quadrupole interaction with the surrounding electric field, was investigated employing Perturbed Angular Correlation (PAC) experiments using NaI(Tl) and BaF2 detectors. Using NaI(Tl) detectors, it was difficult to observe the perturbation, due to the poor time resolution. The BaF2 detector according to the literatures has a shorter light emission decay time constant (0.6 ns), suggested that a better time resolution than that found with the NaI(Tl) detectors could be obtained. A Perturbed Angular Correlation experiment employing BaF2 detectors and a fast-slow coincidence system was set up. The time differential PAC of selenium in solution showed an unperturbed angular correlation pattern. The main problem is the very short half life of the intermediate state of 75Se (0.3 ns), making it difficult to observe the perturbation effect. The time resolution of the system (5.4 ns) will need to be improved by an order of magnitude or more for the investigations to continue.

This thesis considers emission from gamma-ray bursts (GRBs), the most powerful explosions known in the Universe. Most GRBs are likely associated with the final stages of stellar evolution, where the core of a massive star collapses, and gives birth to a highly compact object such as a neutron star or black hole. The wide energy range of the Fermi Gamma-ray Space Telescope allows for unprecedented studies of GRBs. Fermi data is used to study the emission released at the photosphere of the relativistic outow ejected from the central compact object. The thesis present studies of two of the strongest GRBs ever detected; GRB 090902B (Papers I, II) and GRB 110721A (Paper III). Photospheric emission is identied and its properties are studied for both GRBs. For the first time, observational evidence is found for spectral broadening of photospheric emission. Motivated by these results, possible mechanisms to make the emission from the photosphere appear broader than the Planck spectrum are examined. Two separate theoretical explanations are presented. Apart from the possibility of energy dissipation below the photosphere (Paper II), geometrical effects in outflows with angle dependent properties is shown to significantly broaden the photospheric spectrum (Paper IV). Most importantly, the observed spectrum below the peak energy may become significantly softer inthe latter case. This thesis thus concludes that photospheric emission in GRBs may be more common than previously thought. This is because the emission spectrum from the jet photosphere does not necessarily need to be a Planck function. On the contrary it is shown that broader and/or multicomponent spectra naturally arise, consistent with what is generally observed. In particular, the thesis presents a new mechanism for spectral broadening due to geometrical effects, which must be taken into consideration in the study of GRB emission.

QC 20120907

Multi-messenger astronomy is a very hot topic in the astrophysical community. A messenger is something that carries information. Different astrophysical messenger types are photons, cosmic rays, neutrinos, and gravitational waves. They all carry unique and complementary information to one another. The idea with multi-messenger astronomy is that the more different types of messengers one can obtain from the same event, the more complete the physical picture becomes. In this thesis I study the multi-messenger emission from gamma-ray bursts (GRBs), the most luminous events known in the Universe. Specifically, I study the connection of GRBs to extremely energetic particles called ultra-high-energy cosmic rays (UHECRs). UHECRs have unknown origin despite extensive research. GRBs have long been one of the best candidates for the acceleration of these particles but a firm connection is yet to be made. In Paper I and Paper II, we study the possible GRB-UHECR connection by looking at the electromagnetic radiation from electrons that would also be accelerated together with the UHECR. My conclusion is that the signal from these electrons does not match current GRB observation, disfavoring that a majority of UHECRs comes from GRBs.
”Multi-messenger astronomy” (mångbudbärarastronomi, fri översättning) är ett väldigt aktuellt område inom astrofysiken just nu. En meddelare är någonting som bär på information. Olika meddelartyper inom astrofysiken är fotoner, kosmisk strålning, neutriner och gravitations vågor. Dessa har alla unik och olika typ av information som kompletterar varandra. Idén bakom multi-meddelare-astronomi är att ju fler olika meddelartyper vi kan upptäcka från samma event, desto mer komplett blir vår fysikaliska tolkning. I denna avhandling studerar jag multi-meddelare emission från gammablixtar (GRBs), de mest ljusstarka företeelser vi känner till i Universum. Mer specifikt, så studerar jag kopplingen mellan GRBs och ultraenergetisk kosmisk strålning (UHECRs). Ursprunget till UHECRs är fortfarande okänt trots långt pågående forskning. GRBs har länge varit en av de mest lovande accelerationskandidaterna men än så länge finns inga fasta bevis. I Paper I och Paper II studerar vi den möjliga GRB-UHECR kopplingen genom att studera den elektromagnetiska strålningen från elektronerna som även de skulle bli accelererade tillsammans med UHECRs. Min slutsats är att strålningen från elektronerna inte matchar observationer från GRBs, vilket talar emot att en majoritet av UHECRs kommer från GRBs.

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.

Gamma-ray bursts (GRBs) are the most luminous transient events in the Universe, and as such are associated with some of the most extreme processes in nature. They come in two types: long and short, nominally separated either side of a two second divide in gamma-ray emission duration. The short class (those with durations of less than two seconds) are believed to be due to the merger of two compact objects, most likely neutron stars. Within this population, a small subsection exhibit an apparent extra high-energy emission feature, which rises to prominence several seconds after the initial emission event. These are the extended emission (EE) bursts. This thesis investigates the progenitors of the EE sample, including what drives them, and where they fit in the broader context of short GRBs. The science chapters outline a rigorous test of the magnetar model, in which the compact object merger results in a massive, rapidly-rotating neutron star with an extremely strong magnetic field. The motivation for this central engine is the late-time plateaux seen in some short and EE GRBs, which can be interpreted as energy injection from a long-lived central engine, in this case from the magnetar as it loses angular momentum along open field lines. Chapter 2 addresses the energy budget of such a system, including whether the EE component is consistent with the rotational energy reservoir of a millisecond neutron star, and the implications the model has for the physical properties of the underlying magnetar. Chapter 3 proposes a potential mechanism by which EE may arise, and how both classes may be born within the framework of a single central engine. Chapter 4 addresses the broadband signature of both short and EE GRBs, and provides some observational tests that can be used to either support or contradict the model.

This work is concerned with the detection of pulsed TeV gamma ray emission from a number of X-ray binary systems by the use of the atmospheric Cerenkov technique. Chapters 1 and 2 give an overview of the development of gamma ray astronomy, with emphasis placed on progress made in the detection of TeV gamma rays by their Cerenkov radiation in the atmosphere. Chapters 3 and 4 describe the University of Durham atmospheric Cerenkov telescopes, which were used to make the observations reported in this work, and the standard data processing and analysis procedures adopted. The main part of the thesis deals with the application of these techniques to observations of five X-ray binaries. After a review of the properties of such objects in Chapter 5, Chapters 6 and 7 deal specifically with the results for two of the systems considered to be among the most likely candidates to give a detectable TeV photon flux; Centaurus X-3 and Vela X-1. A study of all data recorded on Cen X-3 over the course of six years suggests the presence of a weak gamma ray flux pulsed at the X-ray period. Previous reports of stronger emission near the ascending node of the orbit are confirmed here. For Vela X-1, the analysis of a dataset recorded during a single dark moon interval reveals evidence for two short outbursts of pulsed TeV gamma ray emission. Chapter 8 reports the series of observations made of SMC X-1, 4U1626-67 and X0G21-72, and upper limits are placed on the TeV gamma ray emission from each. Finally, the results reported here are compared with the predictions of a number of theoretical models, some of which are found to give good agreement with the limits and detections derived in this work. A discussion of the status of this field and future observational prospects is also given.

Includes bibliographical references (p. [102]-109).
The 1- radiation following the interactions of 1271 on 197 Au and 194Pt at ELAB = 730 MeV has been studied. The beam energy is approximately 9.5% above the Coulomb barrier. The aim of the present work is to study multi-nucleon transfer to and from the target. At energies above the Coulomb barrier, stripping and pickup reactions occur, quasi-elastic and deep-inelastic events dominate, with the target-like and projectile-like fragments remaining in contact over a sufficient period of time for degree of mass and NIZ ratio equilibration to occur. Relative intensities of various target-like fragments as well as projectile-like fragments have been extracted using the RADWARE and GRAZING program respectively. The spectroscopy of the fragments has been investigated by 1-1 coincidence techniques using the AFRODITE Spectrometer from the iThemba Laboratories. Isotopes of Au and Pt have been observed as well as other nuclei having lost or gained one to two protons in the process. Q-values are also calculated and plotted versus the relative intensities. The results of these plots are compared with the predictions of the GRAZING program. The aim of the present work is to determine whether the unpaired proton from both the projectile and the target influences the transfer of nucleons and whether the transfer is done in purely statistical way or again if the unpaired proton does playa part in the transfer. It was found that for both 1271 on 197 Au and 194Pt at ELAB = 730 MeV, the maximum number of transferred nucleons was only 4- and that the predictions from the GRAZING program do not agree with the extracted relative intensities from RADWARE.

Gamma-ray bursts (GRBs) are brief and sudden explosions radiating most of their energy in the soft γ-ray band ( 100 keV). In the context of multimessenger astroparticle physics recent observations of GRBs provide an excellent benchmark for testing theoretical models of high energy emission mechanisms. Acceleration of hadrons in the engine is expected to produce high energy neutrinos and gamma-rays simultaneously via π±/π0 decays, thus reinforcing the motivation for coincident searches in km3 neutrino telescopes. The Waxman-Bachall spectra and the corresponding expected neutrino rates in IceCube are derived here for GRB090510 amd GRB090902B recently detected by the Fermi Large Area Telescope. The implications of the significant detection of deviations from the Band function fit in photon spectra and a model that explains these extra-components in terms of π0-decay photons are presented here and the relevance to neutrino astronomy is shown.

Since the first introduction of reconstructive tomography in medicine more than a decade ago, research into this technique has continued to arrest the interest of a growing number of scientists especially in the area of industrial non-destructive testing. It is thus an advantage for a laboratory to have a test rig that combines the various Imaging modalities using ionising radiations. Such a test rig has been designed and built around a BBC-B microcomputer complete with its own display system. It combines the ability for transmission and emission tomography with a capability for Compton scattering imaging. Imaging characteristics of the rig including the detectors efficiency, response, collimating systems line spread functions, resolution and the modulation transfer functions are determined. A model has been established to numerically calculate accurately the scattering volume and predict the scattering field at any scattering angle for bore-hole type of collimation. Images of aluminium phantom with lead and brass inclusions have been used to demonstrate the particular suitability of the Compton scattering technique for detecting dense materials within a low density medium. The use of an attenuation correction method for the scattered photons has proved very successful in improving contrast and signal-to-noise ratio of the images. None of the established imaging methods has proved capable of elemental distribution analysis and the methods used in elemental analysis lack the spatial information provided in imaging. A new and novel method is presented in this work that combines the elemental capability of neutron activation analysis with the spatial information of emission tomography. This method has been termed neutron induced gamma-ray emission tomography (NIGET). NIGET images obtained of a freeze-dried water pellet, a piece of human tibia and a study of the diffusion of a preservative solution in a sample of Scots-pine, have been used to demonstrate the potentials of this method.

[EN] Positron Emission Tomography (PET) is a non-invasive nuclear medical imaging modality that makes it possible to observe the distribution of metabolic substances within a patient's body after marking them with radioactive isotopes and arranging an annular scanner around him in order to detect their decays. The main applications of this technique are the detection and tracing of tumors in cancer patients and metabolic studies with small animals. The Electronic Design for Nuclear Applications (EDNA) research group within the Instituto de Instrumentación para Imagen Molecular (I3M) has been involved in the study of high performance PET systems and maintains a small experimental setup with two detector modules. This thesis is framed within the necessity of developing a new data acquisition system (DAQ) for the aforementioned setup that corrects the drawbacks of the existing one. The main objective is to define a DAQ architecture that is completely scalable, modular, and guarantees the mobility and the possibility of reusing its components, so that it admits any extension of modification of the setup and it is possible to export it directly to the configurations used by other groups or experiments. At the same time, this architecture should be compatible with the best possible resolutions attainable at the present instead of imposing artificial limits on system performance. In particular, the new DAQ system should outperform the previous one. As a first step, a general study of DAQ arquitectures is carried out in the context of experimental setups for PET and other high energy physics applications. On one hand, the conclusion is reached that the desired specifications require early digitization of detector signals, exclusively digital communication between modules, and the absence of a centralized trigger. On the other hand, the necessity of a very precise distributed synchronization scheme between modules becomes apparent, with errors in the order of 100 ps, and operating directly over the data links. A study of the existing methods reveals their severe limitations in terms of achievable precision. A theoretical analysis of the situation is carried out with the goal of overcoming them, and a new synchronization algorithm is proposed that is able to reach the desired resolution while getting rid of the restrictions on clock alignment that are imposed by virtually all usual schemes. Since the measurement of clock phase difference plays a crucial role in the proposed algorithm, extensions to the existing methods are defined and analyzed that improve them significantly. The proposed scheme for synchronism is validated using commercial evaluation boards. Taking the proposed synchronization method as a starting point, a DAQ architecture for PET is defined that is composed of two types of module (acquisition and concentration) whose replication makes it possible to arrange a hierarchic system of arbitrary size, and circuit boards are designed and commissioned that implement a realization of the architecture for the particular case of two detectors. This DAQ is finally installed at the experimental setup, where their synchronization properties and resolution as a PET system are characterized and its performance is verified to have improved with respect to the previous system.
[ES] La Tomografía por Emisión de Positrones (PET) es una modalidad de imagen médica nuclear no invasiva que permite observar la distribución de sustancias metabólicas en el interior del cuerpo de un paciente tras marcarlas con isótopos radioactivos y disponer después un escáner anular a su alrededor para detectar su desintegración. Las principales aplicaciones de esta técnica son la detección y seguimiento de tumores en pacientes con cáncer y los estudios metabólicos en animales pequeños. El grupo de investigación Electronic Design for Nuclear Applications (EDNA) del Instituto de Instrumentación para Imagen Molecular (I3M) ha estado involucrado en el estudio de sistemas PET de alto rendimiento y mantiene un pequeño setup experimental con dos módulos detectores. La presente tesis se enmarca dentro de la necesidad de desarrollar un nuevo sistema de adquisición de datos (DAQ) para dicho setup que corrija los inconvenientes del ya existente. En particular, el objetivo es definir una arquitectura de DAQ que sea totalmente escalable, modular, y que asegure la movilidad y la posibilidad de reutilización de sus componentes, de manera que admita cualquier ampliación o alteración del setup y pueda exportarse directamente a los de otros grupos o experimentos. Al mismo tiempo, se desea que dicha arquitectura no limite artificialmente el rendimiento del sistema sino que sea compatible con las mejores resoluciones disponibles en la actualidad, y en particular que sus prestaciones superen a las del DAQ instalado previamente. En primer lugar, se lleva a cabo un estudio general de las arquitecturas de DAQ para setups experimentales para PET y otras aplicaciones de física de altas energías. Por un lado, se determina que las características deseadas implican la digitalización temprana de las señales del detector, la comunicación exclusivamente digital entre módulos, y la ausencia de trigger centralizado. Por otro lado, se hace patente la necesidad de un esquema de sincronización distribuida muy preciso entre módulos, con errores del orden de 100 ps, que opere directamente sobre los enlaces de datos. Un estudio de los métodos ya existentes revela sus graves limitaciones a la hora de alcanzar esas precisiones. Con el fin de paliarlos, se lleva a cabo un análisis teórico de la situación y se propone un nuevo algoritmo de sincronización que es capaz de alcanzar la resolución deseada y elimina las restricciones de alineamiento de reloj impuestas por casi todos los esquemas usuales. Dado que la medida de desfase entre relojes juega un papel crucial en el algoritmo propuesto, se definen y analizan extensiones a los métodos ya existentes que suponen una mejora sustancial. El esquema de sincronismo propuesto se valida utilizando placas de evaluación comerciales. Partiendo del método de sincronismo propuesto, se define una arquitectura de DAQ para PET compuesta de dos tipos de módulos (adquisición y concentración) cuya replicación permite construir un sistema jerárquico de tamaño arbitrario, y se diseñan e implementan placas de circuito basadas en dicha arquitectura para el caso particular de dos detectores. El DAQ así construído se instala finalmente en el setup experimental, donde se caracterizan tanto sus propiedades de sincronización como su resolución como sistema PET y se comprueba que sus prestaciones son superiores a las del sistema previo.
[CAT] La Tomografia per Emissió de Positrons (PET) és una modalitat d'imatge mèdica nuclear no invasiva que permet observar la distribució de substàncies metabòliques a l'interior del cos d'un pacient després d'haver-les marcat amb isòtops radioactius disposant un escàner anular al seu voltant per a detectar la seua desintegració. Aquesta tècnica troba les seues principals aplicacions a la detecció i seguiment de tumors a pacients amb càncer i als estudis metabòlics en animals petits. El grup d'investigació Electronic Design for Nuclear Applications (EDNA) de l'Instituto de Instrumentación para Imagen Molecular (I3M) ha estat involucrat en l'estudi de sistemes PET d'alt rendiment i manté un petit setup experimental amb dos mòduls detectors. Aquesta tesi neix de la necessitat de desenvolupar un nou sistema d'adquisició de dades (DAQ) per al setup esmentat que corregisca els inconvenients de l'anterior. En particular, l'objectiu és definir una arquitectura de DAQ que sigui totalment escalable, modular, i que asseguri la mobilitat i la possibilitat de reutilització dels seus components, de tal manera que admeta qualsevol ampliació o alteració del setup i pugui exportar-se directament a aquells d'altres grups o experiments. Al mateix temps, es desitja que aquesta arquitectura no introduisca límits artificials al rendiment del sistema sinó que sigui compatible amb les millors resolucions disponibles a l'actualitat, i en particular que les seues prestacions siguin superiors a les del DAQ instal.lat amb anterioritat. En primer lloc, es porta a terme un estudi general de les arquitectures de DAQ per a setups experimentals per a PET i altres aplicacions de física d'altes energies. Per una banda, s'arriba a la conclusió que les característiques desitjades impliquen la digitalització dels senyals del detector el més aviat possible, la comunicació exclusivament digital entre mòduls, i l'absència de trigger centralitzat. D'altra banda, es fa palesa la necessitat d'un mecanisme de sincronització distribuïda molt precís entre mòduls, amb errors de l'ordre de 100 ps, que treballi directament sobre els enllaços de dades. Un estudi dels mètodes ja existents revela les seues greus limitacions a l'hora d'assolir aquest nivell de precisió. Amb l'objectiu de pal.liar-les, es duu a terme una anàlisi teòrica de la situació i es proposa un nou algoritme de sincronització que és capaç d'obtindre la resolució desitjada i es desfà de les restriccions d'alineament de rellotges imposades per gairebé tots els esquemes usuals. Atès que la mesura del desfasament entre rellotges juga un paper cabdal a l'algoritme proposat, es defineixen i analitzen extensions als mètodes ja existents que suposen una millora substancial. L'esquema de sincronisme proposat es valida mitjançant plaques d'avaluació comercials. Prenent el mètode proposat com a punt de partida, es defineix una arquitectura de DAQ per a PET composta de dos tipus de mòduls (d'adquisició i de concentració) tals que la replicació d'aquests elements permet construir un sistema jeràrquic de mida arbitrària, i es dissenyen i implementen plaques de circuit basades en aquesta arquitectura per al cas particular de dos detectors. L'electrònica desenvolupada s'instal.la finalment al setup experimental, on es caracteritzen tant les seues propietats de sincronització com la seua resolució com a sistema PET i es comprova que les seues prestacions són superiors a les del sistema previ.
Aliaga Varea, RJ. (2016). Development of a data acquisition architecture with distributed synchronization for a Positron Emission Tomography system with integrated front-end [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/63271
TESIS
Premiado

This thesis studies the broadband behaviour of GRBs by fitting a detailed spectral/temporal model to both the prompt and afterglow hard and soft X-ray emission observed by the Swift satellite. The prompt emission is decomposed into pulses which are fitted individually while the afterglow is modelled using a smoothly varying broad pulse which evolves into a power-law decay at late times. Using this model a comprehensive study of GRB 080310 is presented and followed by similar analyses of GRB 061121, GRB 080810 and GRB 081008. The optical behaviour is found to be inconsistent with the high-energy model: a spectral break between the X-ray and optical band is necessary and for many prompt pulses the self-absorption mechanism is required. The latter three bursts have optical afterglows that are shown to be inconsistent with those fitted to the X-ray regime, peaking earlier in the lower energy bands and requiring a low-energy spectral break. The prompt optical emission seen from GRB 061121 has pulse-like features which match reasonably well with contemporaneous high-energy features, but have longer durations. The same model was used to study the expected evolution of GRB properties when moved to higher redshifts. Using a sample of bright Swift GRBs, the changes in measured duration with redshift were found to be driven by a combination of time dilation, gradual loss of pulse tails and sudden loss of pulses as the flux falls below instrumental sensitivity. A realistic sample of synthetic bursts is produced which, when simulated at high redshift, are found to be significantly longer in duration that the observed high redshift GRBs. Also demonstrated is that several bright bursts seen by Swift could be detected if they occurred at a redshift > 10 encouraging the use of GRBs as probes of the early Universe.

The large flashes of radiation that are observed in GRBs are generally believed to arise in a relativistic jetted outflow. This thesis addresses the question of how and where in the jet this radiation is produced. It further explores the jet properties that can be inferred from the observations made by the Fermi GST that regularly observes GRBs in the range 8 keV - 300 GeV.  In my analysis I focus on the observational effects of the emission from the jet photosphere. I show that the photosphere has an important role in shaping the observed radiation spectrum and that its manifestations can significantly vary between bursts. For bursts in which the photospheric  emission component can be identified, the dynamics of the flow can be explored by determining the  jet Lorentz factor and the position of the jet nozzle. I also develop the theory of how to derive the properties of the outflow for general cases. The spectral analysis of the strong burst GRB110721A reveals a two-peaked spectrum, with the peaks evolving differently. I conclude that three main flow quantities can describe the observed spectral behaviour in bursts:  the luminosity, the Lorentz factor, and the nozzle radius. While the photosphere can appear like a pure blackbody it can also be substantially broadened, due to dissipation of the jet energy below the photosphere. I show that Comptonisation of the blackbody can shape the observed spectra and describe its evolution. In particular this model can very well explain GRB110920A which has two prominent breaks in its spectra.  Alternative models including synchrotron emission leads to severe physical constraints, such as the need for very high electron Lorentz factors, which are not expected in internal shocks. Even though different manifestations of the photospheric emission can explain the data, and lead to ambiguous interpretations, I argue that dissipation below the photosphere is the most important process in shaping the observed spectral shapes and evolutions.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: In press. Paper 5: Submitted.

The quest for the first detection of a galaxy cluster in the high energy gamma-ray regime is ongoing, and even though clusters are observed in several other wave-bands, there is still no firm detection in gamma-rays. To complement the observational efforts we estimate the gamma-ray contributions from both annihilating dark matter and cosmic-ray (CR) proton as well as CR electron induced emission. Using high-resolution simulations of galaxy clusters, we find a universal concave shaped CR proton spectrum independent of the simulated galaxy cluster. Specifically, the gamma-ray spectra from decaying neutral pions, which are produced by CR protons, dominate the cluster emission. Furthermore, based on our derived flux and luminosity functions, we identify the galaxy clusters with the brightest galaxy clusters in gamma-rays. While this emission is challenging to detect using the Fermi satellite, major observations with Cherenkov telescopes in the near future may put important constraints on the CR physics in clusters. To extend these predictions, we use a dark matter model that fits the recent electron and positron data from Fermi, PAMELA, and H.E.S.S. with remarkable precision, and make predictions about the expected gamma-ray flux from nearby clusters. In order to remain consistent with the EGRET upper limit on the gamma-ray emission from Virgo, we constrain the minimum mass of substructures for cold dark matter halos. In addition, we find comparable levels of gamma-ray emission from CR interactions and dark matter annihilations without Sommerfeld enhancement.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted.

Thesis (Ph. D.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Globular clusters, such as M13, are very dense star clusters and are known to contain many more millisecond pulsars per unit mass than the galaxy as a whole. These pulsars are concentrated in the core regions of globulars and are expected to generate relativistic winds of electrons. Such energetic electrons may then interact with the intense field of optical photons, which is supported by the numerous normal stars of the cluster, to generate Very High-Energy (VHE) gamma rays. Herein, this emission model, as imple- mented by Bednarek & Sitarek (2007), is described and justified in more detail and data from observations of M13, undertaken to confront this model, are analysed. No evidence for VHE gamma-ray emission from M13 is found. A decorrelated, integral upper limit of 0.306 * 10^−12 cm^−2 s^−1 above 0.8 TeV, at a confidence level of 95%, is determined. Spectral upper limits are also determined and compared to emission curves presented in Bednarek & Sitarek (2007). A detailed examination of the parameters of the model is performed and it is found that the predicted curves were based upon over-optimistic estimations of several of these. Nonetheless, the model can be related to existing theories of pulsar winds and, thereby, it is found that the acceleration of electrons in millisec- ond pulsar winds (outside pulsar light-cylinders) to TeV energies is excluded by these observations, under self-consistent assumptions of the properties of this population of millisecond pulsars.
Les amas globulaires, tels que M13, sont des amas d'étoiles très denses et sont connus pour contenir beaucoup plus de pulsars milliseconde par unité de masse que la galaxie dans son ensemble. Ces pulsars sont concentrés dans les régions centrales d'amas globulaires et sont supposés générer des vents relativistes d'électrons. Ces électrons énergétiques peuvent alors interagir avec le champ intense de photons optiques, qui est soutenu par les nombreuses étoiles normales de l'amas, afin de générer des rayons gamma de Très Haute Énergie (THE). Dans la présente thèse, ce modèle d'émission, mis en oeuvre par Bednarek & Sitarek (2007), est décrit et justifié de manière plus détaillée et des données, recueillies à partir d'observations de M13, ont été analysées dans le but de confronter ce modèle. Aucune preuve d'émission des rayons gamma THE de M13 n'a été trouvée. Une limite supérieure intégrale et décorrélée est déterminée, soit 0.306 * 10^−12 cm^−2 s^−1 en dessus de 0.8 TeV, à un niveau de confiance de 95%. Des limites supérieures spectrales sont également déterminées et comparées aux courbes d'émission présentées dans Bednarek & Sitarek (2007). L'examen détaillé des paramètres du modèle révèle que les courbes attendues étaient fondées sur des estimations trop optimistes de plusieurs de ces paramètres. Néanmoins, le modèle peut être lié aux théories existantes des vents des pulsars et, ce faisant, à travers ces observations, on trouve que l'accélération des électrons dans les vents des pulsars millisecondes (en dehors des cylindres lumièriques des pulsars) aux énergies TeV est à exclure, selon des hypothèses auto-cohérentes des propriétés de cette population des pulsars millisecondes.

Thesis (Ph. D.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

This thesis treats the findings and current theories of the active galactic nuclei 3454.3. It mainly aims to describe the behavior of the specific source in the gamma-ray energy band as recorded by the Fermi-LAT satellite. Using NASA’s computational tools and all recorded data the variability of the source was assessed. As the received flux from the source varies substantially over time several periods of time for which the flux differs considerably were analysed. Spectral analysis for the various time-frames was performed in order to determine how we best can describe the results from each period. The Fermi-LAT results were then examined in the wider context of multi-wavelength astronomy. Finally, data retrieved at all wavelengths were modeled and compared in accordance with currently held theories.

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.

Les sursauts gamma (GRBs pour "Gamma-Ray Bursts" en anglais) sont de brèves bouffées très énergétiques de rayonnement de haute énergie qui sont émises sur de courtes échelles de temps (fraction de seconde à plusieurs minutes). L'émission intense des sursauts gamma à haute énergie est supposée provenir d'un trou noir de masse stellaire nouvellement formé, accompagné d'un vent collimaté (i.e. un jet) se propageant à vitesse relativiste. L'émission est observée suivant deux phases successives, la phase prompte très erratique, et la phase de rémanence, moins lumineuse. Les deux instruments embarqués sur le satellite Fermi, le "Gamma-ray Burst Monitor" (GBM) et le "Large Area Telescope" (LAT), permettent d'étudier l'émission prompte des sursauts gamma sur une grande plage d'énergie (de ~10 keV à ~100 GeV). L'objectif principal de ma thèse est l'analyse et l'interprétation des propriétés spectrales et temporelles de l'émission prompte des GRBs observés par Fermi, en particulier avec les nouvelles données du LAT (Pass 8) qui ont été rendues publiques en juin 2015.La première partie de mon travail est une analyse spectrale résolue en temps de la phase prompte du sursaut GRB 090926A avec les données du GBM et du LAT. Mes résultats confirment avec un meilleur niveau de confiance la présence d'une cassure spectrale à ~400 MeV, qui est observée en coincidence avec un pic d'émission très court. Ils révèlent que cette atténuation spectrale est présente durant toute l'émission prompte du sursaut, et que l'énergie de cassure augmente jusqu'au GeV. L'interprétation de la cassure spectrale en termes d'absorption gamma ou de courbure naturelle du spectre d'émission Compton inverse (CI) dans le régime Klein-Nishina fournit des contraintes fortes sur le facteur de Lorentz du jet. Mes résultats conduisent en outre à des rayons d'émission R ∼10^14 cm qui sont compatibles avec une origine interne de l'émission du keV au GeV au-dessus de la photosphère du jet.La seconde partie de mon travail est une exploration du modèle de chocs internes développé par des collaborateurs à l'Institut d'Astrophysique de Paris (IAP). Ce modèle simule la dynamique du jet et les processus d'émission (synchrotron et CI) d'une population d'électrons accélérés aux chocs. J'ai simulé la réponse instrumentale de Fermi à un sursaut synthétique fourni par ce code numérique, et j'ai construit une fonction paramétrique qui peut être utilisée pour ajuster le modèle aux spectres de sursauts du keV au MeV. J'ai appliqué cette fonction avec succès à un échantillon de 64 sursauts brillants détectés par le GBM. J'ai aussi confronté le modèle de l'IAP au spectre d'émission prompte de GRB 090926A. Mes résultats montrent un bon accord, et j'ai identifié quelques pistes pour les améliorer. Les spectres synthétiques sont plus larges que tous les spectres dans l'échantillon du GBM. En conséquence, je discute brièvement quelques pistes de développements théoriques qui pourraient améliorer l'accord du modèle avec les observations, ainsi que des avancées observationnelles attendues dans le futur
Gamma-Ray Bursts (GRBs) are very energetic and brief flashes of high-energy radiations which are emitted in a short time scale (fraction of a second to several minutes). The GRB bright emission is thought to be powered by a newly formed stellar-mass black hole that is accompanied by a collimated outflow (i.e. a jet) moving at a relativistic speed. The emission is observed as two successive phases: the highly variable “prompt” phase and the late and less luminous “afterglow” phase. The two instruments on board the Fermi space telescope, the Gamma-ray Burst Monitor (GBM) and the Large Area Telescope (LAT), allow the study of GRB prompt emission over a broad energy range (from ~10 keV to ~100 GeV). In June 2015, a new set of LAT data (Pass 8) was publicly released, which were generated using improved algorithms of reconstruction and classification of gamma-ray events. The main goal of my thesis is the analysis and interpretation of the spectral and temporal properties of the prompt emission phase of the GRBs observed by Fermi, especially using LAT Pass8 data.In the first part of my work, I performed a detailed time-resolved spectral analysis of the prompt phase of GRB 090926A with GBM and LAT data. My results confirm with a greater significance the spectral break at ∼400 MeV that is observed during a fast variability pulse, and they also reveal the presence of a spectral attenuation throughout the GRB prompt emission, as well as an increase of the break energy up to the GeV domain. I interpreted the spectral break in terms of gamma-ray absorption or as a natural curvature of the inverse Compton (IC) emission in the Klein-Nishina regime. Strong constraints on the jet Lorentz factor were obtained in both scenarios. My results lead also to emission radii R ∼10^14 cm, which are consistent with an internal origin of both the keV-MeV and GeV prompt emissions above the jet photosphere.The second part of my work is an exploration of the internal shock model that has been developed by collaborators at the "Institut d'Astrophysique de Paris" (IAP). This model simulates the GRB jet dynamics and the radiations (synchrotron and IC processes) from a population of shock-accelerated electrons. I simulated the response of the Fermi instruments to the synthetic GRB spectra provided by this numerical code. From these simulations, I built a new parametric function that can be used to fit the keV-MeV spectra of GRBs with the model. I applied successfully this function to a sample of 64 GBM bright GRBs. I confronted also the IAP model to the prompt emission spectrum of GRB 090926A. I obtained a relatively good agreement and I identified a couple of solutions that may improve it. The synthetic spectra are wider than any GRB spectra in the GBM sample. I present some theoretical developments that could improve the data-model agreement in the future, and I discuss possible advances from future GRB missions as well

The radiative mechanism responsible for the prompt gamma-ray burst (GRB) emission remains elusive. For the last decade, optically thin synchrotron emission from shocks internal to the GRB jet appeared to be the most plausible explanation. However, the synchrotron interpretation is incompatible with a significant fraction of GRB observations, highlighting the need for new ideas. In this thesis, it is shown that the narrow, dominating component of the prompt emission from the bright GRB090902B is initially consistent only with emission released at the optically thick jet photosphere. However, this emission component then broadens in time into a more typical GRB spectrum, which calls for an explanation. In this thesis, a previously unconsidered way of broadening the spectrum of photospheric emission, based on considerations of the lateral jet structure, is presented and explored. Expressions for the spectral features, as well as polarization properties, of the photospheric emission observed from structured, relativistic jets are derived analytically under simplifying assumptions on the radiative transfer close to the photosphere. The full, polarized radiative transfer is solved through Monte Carlo simulations, using a code which has been constructed for this unique purpose. It is shown that the typical observed GRB spectrum can be obtained from the photosphere, without the need for additional, commonly assumed, physical processes (e.g. energy dissipation, particle acceleration, or additional radiative processes). Furthermore, contrary to common expectations, it is found that the observed photospheric emission can be highly linearly polarized (up to $\sim 40 \, \%$). In particular, it is shown that a shift of $\pi/2$ of the angle of polarization is the only shift allowed by the proposed model, consistent with the only measurement preformed to date. A number of ways to test the theory is proposed, mainly involving simultaneous spectral and polarization measurements. The simplest measurement, which tests not only the proposed theory but also common assumptions on the jet structure, involves only two consecutive measurements of the angle of polarization during the prompt emission.

QC 20131204

In our Galaxy, supernova remnants and pulsars are the two most numerous populations of non-thermal objects. The goal of this thesis is to study the extreme gamma-ray emission from these two astrophysical objects with Fermi -LAT and MAGIC. In particular, supernova remnants Cassiopeia A and SNR G24.7+0.6 and the Crab pulsar. Cassiopeia A, one of the historical supernova remnants and the prime candidate of its class to be a PeVatron accelerator, has been discarded as so since we provided the first measurement of a turn-off in the gamma-ray spectrum at 3 TeV, implying the emission observed is produced by the decay of neutral pions, produced in proton- proton interactions of a parent population of accelerated protons with an energy cut-off at about 10TeV. Such a maximum energy of accelerated cosmic rays in Cassiopeia A falls short to explain the high energy end ( PeV) of the Galactic cosmic ray spectrum. Considering that Cassiopeia A was the main PeVatron candidate, the results obtained in this work challenge the existence of supernova remnants as galactic Pevatrons and therefore the popular conviction that supernova remnants are the main source of Galactic cosmic ray up to the knee. In the case of SNR G24.7+0.6, the remnant is evolving in a dense medium and might be interacting with the CO-rich surrounding. The observations performed allowed us to detect for the first time the counterpart of the radio emission, MAGIC J1835–069, from 60MeV up to 5TeV. This very high energy emission results from proton-proton interactions between the runaway protons from the supernova remnant and a nearby molecular cloud. These observations of the field of view of SNR G24.7+0.6, also resulted in the detection of another new source, MAGIC J1837–073, that is likely to be associated with a stellar cluster as suggested by its localization in a region rich in molecular content and crowded of sources. The total energy obtained in accelerated protons can be explained assuming a quasi-continuous injection of cosmic rays during the cluster lifetime. The second part of this thesis is focused on the study and understanding of the Crab pulsar, the young and most energetic pulsar in our galaxy. Observations carried out with MAGIC resulted in the first ever detection of very energetic pulsed emission from a pulsar, reaching up to about 1.5 TeV. Moreover, the light curve of the Crab above 400 GeV shows two peaks synchronized with those measured at lower energies. Such extremely energetic pulsed emission has to be produced by electrons with very high Lorentz factor scattering low energy photons in the vicinity of the light cylinder, either inside or outside of it. Currently, none of the postulated models is yet capable of reproducing at the same time the light curve and the spectral shape for both peaks above 400 GeV.
Esta tesis tiene como objetivo el estudio de la emisión extrema de rayos gamma proveniente de remanentes de supernova y el pulsar del Cangrejo. Dos remanentes de supernova han sido observados tanto con Fermi, como con MAGIC; Cassiopeia A y SNR G24.7+0.6. Cassiopeia A, el principal candidato de su clase a revelarse como PeVatrón, ha sido descartado como tal, al haberse detectado un corte en el espectro de rayos gamma en torno a 3 TeV, lo cual implica que, la emisión observada es producida por el de- caimiento de piones neutros, originados en colisiones protón-protón por una población de protones que presenta un corte exponencial en su espectro en torno a una energía de 10 TeV. Esta energía máxima a la que son acelerados estos rayos cósmicos pone en serias dudas la existencia de remanentes de supernova que se comporten como PeVa- trones, y por tanto, la teoría de que éstos son la fuente principal de rayos cósmicos galácticos. En el caso de SNR G24.7+0.6, con las observaciones llevadas a cabo, hemos conseguido detectar por primera vez la contrapartida de la emisión radio a energías desde 60 MeV hasta 5 TeV, MAGIC J1835–069, producida por protones que escapan del remanente de supernova y que interaccionan con una nube molecular cercana. En estas mismas observaciones, hemos podido detectar otra fuente nueva, MAGIC J1837–073, la cual está asociada, muy probablemente, con un cumulo estelar tal y como sugiere su lo- calización. Su emisión puede ser explicada asumiendo una inyección casi continua de rayos cósmicos durante la totalidad de la vida estimada del cumulo estelar. Por otra parte, el estudio del púlsar del Cangrejo, llevado a cabo con MAGIC ha re- sultado en el descubrimiento de emisión pulsada hasta 1.5 TeV, refutando cualquiera de los modelos presentados hasta el momento. Además, la curva de luz que carac- teriza la emisión proveniente del púlsar por encima de 400 GeV, presenta dos picos sincronizados en fase con los picos hallados a energías más bajas. Esta emisión, ex- tremadamente energética, únicamente puede ser producida por electrones acelerados hasta factores de Lorentz muy altos en regiones cercanas al cilindro de luz, ya sea en su interior o en su exterior, y que posteriormente colisionan y transfieren su energía a fotones térmicos.

Interpretation of the present gamma-ray data above 100 MeV is discussed in relation to cosmic ray interactions with the atomic and molecular hydrogen in the Galactic plane. The SAS II gamma-ray data are analysed for supportive evidence on the 2CG candidate sources identified from the COS B observations. The strongest sources are confirmed. There is good evidence to suggest that many of the weaker sources are not truly discrete. A Monte-Carlo analysis of the discrete source detection efficiencies suggests that many 2CG sources are unresolved giant molecular clouds, irradiated by the ambient cosmic ray flux. An attempt is made to define a genuine source catalogue. Taking account of the detection efficiencies the net source flux (from both resolved and unresolved sources) is estimated to be 11-23% of the Galactic plane emission. Cosmic ray interactions with the Orion molecular cloud complex are investigated through an analysis of the gamma-ray emission above 100 MeV. There is no evidence for cosmic ray exclusion from the clouds. A new derivation of the CO/H (_2) ratio is obtained. N (_H2) / T ((^12) CO) dv = (3.7 ± 0.6) x 10(^20) at cm (^-2) (K kms (^-1)) (^-1) Contributions to the extragalactic gamma-ray flux from radio galaxies and rich clusters are estimated. The flux may be dominated by emission from these objects. With the estimate of the discrete Galactic source flux and the CO→H (_2) ratio, the radial gamma-ray emissivity is compared to the HI, inferred H (_2) and possible cosmic ray radial densities in the inner Galaxy. It is shown that a moderate cosmic ray gradient overestimates the gamma-ray flux, unless the metal abundance gradient reduces the inferred H (_2) mass.

Esta tesis se centra en el estudio de sistemas binarios compactos de rayos γ, las denominadas binarias de rayos γ, con los telescopios MAGIC. Sólo cinco sistemas son los componentes de este reducido grupo. Todos ellos tienes estrellas masivas, pero sólo se conoce la naturaleza del objeto compacto de una de ellas, que se trata de una estrella de neutrones. Aunque ninguno de ellos muestra pulsaciones (propio de estrellas de neutrones) ni estructuras que se asemejen a jets (típico de agujeros negros), la mayoría de las teorías apuestan a que el objeto compacto de estos objetos es una estrella de neutrones. El escenario más aceptado para explicar la emisión γ de muy alta energía es aquel en el que el viento estelar interactúa con el viento de la estrella de neutrones, acelerando las partículas presentes en el sistema hasta velocidades relativistas, con la consecuente emisión de rayos γ. El esquema de la tesis es el siguiente: • El capítulo 1 es una introducción a la astronomía de rayos γ de muy alta energía. Se presenta un pequeño resumen de la historia de los rayos cósmicos y su relación con los rayos γ. A continuación, se describen los métodos directos para la detección de rayos γ desde el espacio y los métodos indirectos utilizados por observatorios en tierra. Debido a que esta tesis utiliza datos de los telescopios MAGIC, se introduce la técnica IACT y sus fundamentos físicos. • En el capítulo 2, se discuten las restricciones de los telescopios Cherenkov debido a las incertidumbres sistemáticas provocadas por el desconocimiento de las condiciones atmosféricas y la necesidad de corregirlas. Como posible solución, se propone la utilización de sistemas LIDAR y se describe el instrumento de este tipo que está siendo desarrollado y caracterizado en el IFAE. • Los telescopios MAGIC, desde los componentes electrónicos y mecánicos y el software de control, están descritos en el capítulo 3 . Se hace especial hincapié en el sistema de adquisición de datos, en el que la autora de la tesis ha contribuido. La cadena de análisis estándar de MAGIC también se describe en este capítulo, dedicando un apartado especial al análisis bajo condiciones de luna moderada/fuerte. • El capítulo 4 es una introducción a los distintos tipos de sistemas binarios, prestando especial atención a los sistemas binarios en rayos X y en rayos γ. Los posibles escenarios para explicar la emisión gamma de estos últimos se discuten aquí también. • El capítulo 5 es una completa y detallada descripción de la binaria de rayos γ LS I + 61◦303 y se muestran los resultados de una campaña multi-­‐anual. Se investiga la variabilidad anual en la emisión a muy altas energías de esta fuente, así como la posible existencia de una modulación super-­‐orbital en su flujo. Además, se realiza un estudio sobre variabilidad espectral. Finalmente, se estudia la posible correlación entre el flujo en rayos γ de muy alta energía y la pérdida de masa de la estrella, a través de observaciones simultáneas de MAGIC y el telescopio óptico LIVERPOOL. • En el capítulo 6, se describen las observaciones realizadas sobre la candidata a binaria de rayos γ MWC 656. Este sistema es muy interesante debido a que se trata de la primera estrella masiva tipo Be en albergar un agujero negro, probado experimentalmente. • En el capítulo 7 se muestra la búsqueda de emisión γ del sistema binario SS 433, un microquasar que se encuentra sumergido en una nebulosa. • Finalmente, las conclusiones de los estudios realizados y algunas perspectivas de futuro se recogen en el capítulo 8.
This thesis is focused on the study of compact binary systems that emit γ-­‐ ray emission, the so-­‐called γ-­‐ray binaries, with the MAGIC telescopes. The bulk of the non-­‐thermal emission of these systems peaks in the γ-­‐ray domain. Only five systems are the members of this reduced group. All of them host massive stars and a compact object, remnant of a supernova explosions. Only the compact object of one of these binaries is known, a neutron star. Although none of them display pulsations (associated with neutron stars) or double-­‐jet structures (associated with microquasars), most of the theories and observations suggest a neutron star as the compact object. The most accepted scenario to explain the very high energy (VHE) emission of this source class is the pulsar wind scenario. The wind of the massive star and the wind of the neutron star interact, accelerating particles up to relativistic energies with the consequent emission of γ-­‐rayphotons. The outline of the thesis is the following: • Chapter 1 is an introduction to VHE γ-­‐ ray astronomy. First, a brief history of cosmic rays and their relation with γ rays is introduced. Direct methods for the detection of γ rays in outer space and indirect detection techniques on Earth with ground-­‐based observatorios are described. Since this thesis uses data from the MAGIC telescopes, the Imaging Air Cherenkov Technique and its physics principles are introduced. • In Chapter 2, the restrictions of IACTs in terms of the systematic uncertainties due to atmospheric conditions and the need for correcting them is discussed. A LIDAR is introduced as a solution for the next generation of IACTs, the Cherenkov Telescope Array (CTA), to reduce systematic errors and enlarge the duty cycle. The LIDAR which is being developed and characterized at IFAE is described, as well as the performance of this system. • Chapter 3 shows a description of the MAGIC telescopes. The hardware and software components, with a special contribution to the data acquisition system by the author of this thesis, are described. The standard data analysis chain is also collected as well as the special treatment of the data under moderate -­‐ strong moonlight conditions. • Chapter 4 is an introduction to compact binary systems. It describes the large variety of these sources in this Universe, finally focussing in X-­‐ray binaries and γ-­‐ ray binaries. The possible scenarios to account for the γ-­‐ ray emission of these sources are also introduced. • Chapter 5 is the complete and detailed description of the γ-­‐ray binary LS I +61◦303. The results of a multi-­‐year campaign are shown in this Chapter. Studies on the yearly flux variability and the possible existence of a super-­‐orbital modulation in the flux are investigated. Furthermore, searches for spectral variability are performed. Finally, a correlation study of the TeV flux with the mass-­‐loss rate of the Be star through simultaneous observations with an optical telescope is performed. • In Chapter 6, a search for TeV emission of the γ-­‐ray binary candidate MWC 656 is performed. This system is especially interesting for being the first Be star to be proven to host a black hole. • Chapter 7 details the search for VHE γ-­‐ray emission of the binary system SS 433, which is a microquasar embedded in a nebula. It is the only super-­‐critical accretor in the Galaxy and displays hadronic jets emission. • Finally, concluding remarks from the presented studies and future perspectives are discussed in Chapter 8.

Es el propósito de esta tesis estudiar la posibilidad de que regiones con importante actividad en formación estelar sean fuentes de rayos gamma para los actuales y futuros detectores, ya sean detectores de rayos gamma con base en satélites como telescopios Cherenkov situados en la superficie terrestre.
Tras una evaluación fenomenológica positiva de que la emisión de rayos gamma procedente de galaxias con elevada actividad en formación estelar (como las llamadas starburst o las galaxias ultra luminosas en el infrarrojo) esté cerca de la sensibilidad de los actuales detectores de rayos gamma, se han desarrollado y presentado modelos detallados de la emisión difusa multifrecuencia procedente de los dos mejores candidatos, NGC 253 y Arp 220. Se predice que ambas galaxias serán detectables para GLAST, el próximo satélite de rayos gamma con una sensibilidad sin precedentes, y por HESS y MAGIC, los actuales telescopios Cherenkov con mayor sensibilidad, en caso de que éstos dediquen suficiente tiempo de observación a estas galaxias.
En la parte teórica de la tesis se describe también un modelo que propone la emisión de importantes flujos de rayos gamma en regiones de formación estelar dentro de nuestra Galaxia, como serían las asociaciones de estrellas jóvenes del tipo OB. El modelo considera la emisión de rayos gamma a energías cercanas a los TeV mediante interacciones hadrónicas en el sí de vientos estelares de algunas de las estrellas de la asociación, prediciendo a la vez que la emisión a bajas energías está sustancialmente suprimida debido al efecto de modulación que la población de rayos cósmicos primarios sufre al penetrar en el viento estelar. Se discuten brevemente los mejores candidatos entre las asociaciones OB galácticas conocidas.
Finalmente, la tesis recoge un primer análisis de los datos tomados por el Telescopio MAGIC durante la observación de dos regiones de formación estelar. Por una parte, la galaxia ultra luminosa en el infrarrojo más cercana, Arp 220. Por otra parte, TeV J2032+4130, que aún hoy en día sigue siendo una fuente no identificada, y cuyo origen se ha relacionado con la poderosa asociación estelar Cygnus OB2 en repetidas ocasiones. Ninguna de las observaciones ha implicado detección, en consecuencia, se han impuesto límites superiores al flujo de rayos gamma procedente de las fuentes observadas. Sin embargo, a pesar de las pocas horas de observación incluidas en el presente análisis, los límites superiores impuestos por el Telescopio MAGIC para la fuente TeV J2032+4130 están prácticamente al nivel del flujo que el experimento HEGRA detectó para dicha fuente, de manera que un análisis extendido al conjunto completo de datos disponibles, así como futuras observaciones de más larga exposición con el Telescopio MAGIC, podrían proveer resultados interesantes.
Was the aim of this thesis to study the possibility that regions with important activity in star formation may appear as sources of gamma-rays for the current and near future gamma-ray detectors, both ground and space-satellite based.
After a phenomenological positive evaluation of the fact that the gamma-ray emission from galaxies prone of star formation processes (as starburst or ultra luminous infrared galaxies) may be close to the flux sensitivities of the current gamma-ray telescopes, detailed models of the multiwavelength diffuse emission from the two best candidates, NGC 253 and Arp 220, have been presented. It is predicted that they will be detectable by GLAST, the next largest gamma-ray satellite, and by HESS and MAGIC, the current more sensitive Cherenkov Telescopes, in case enough observation time is devoted.
On the other hand, within this thesis it is described a model which proposes the emission of important fluxes of gamma-rays from regions of star formation within our Galaxy, as the stellar association of young OB stars. The model considers the emission of gamma-rays close to TeV energies by hadronic interactions within the stellar winds of some of the stars of the association, predicting at the same time that the emission at lower energies is substantially suppressed due to the modulation effects that the incoming population of primary cosmic rays suffers when penetrating the winds. The best candidates among the galactic OB associations are briefly discussed.
Finally, a first analysis of the data taken by the MAGIC Telescope when observing two of these regions of star formation is described. On one hand, the closest ultra luminous infrared galaxy, Arp 220. On the other, TeV J2032+4130, which is still an unidentified source whose origin has been several times related to the powerful stellar OB association Cygnus OB2. Any of both observations has implied detection, and upper limits to the gamma-ray flux have been imposed. However, although the few hours of observation included in the present analysis, the MAGIC upper limits for TeV J2032+4130 are nearly at the level of the flux detected by the HEGRA experiment, so an analysis extended to the complete set of data available as well as deeper observations of this source with the MAGIC Telescope can provide promising results.

Se puede dividir mi tesis en tres partes: 1. Estudios de la emisi.n gamma de los sistemas binarios LS I +61 303 y LS 5039 a altas energ.as con el Fermi Large Area Telescope (LAT) y el primer descubrimiento de variabilidad superorbital a altas energ.as de la fuente LS I +61 303 Los sistemas binarios de rayos gamma son sistemas estelares cuyo espectro tiene su máximo a altas energías (sin tener en cuenta su emisión térmica). Ha sido detectada desde radio hasta rayos gamma (TeV), el sistema binario LS I +61 303 es muy variable en todas las frecuencias. Una característica de la variabilidad de este sistema es la modulación de su emisión a 26.496 días que coincide con su período orbital. En esta tesis mostramos por primera vez que la emisión gamma de LS I +61 303 presenta también una variabilidad superorbital con un período de 1667 días. Esta modulación es más presente en fases orbitales alrededor de apastro, aunque no introduce un cambio visible cerca de periastro. Además, se observa una aparición y desaparición de la variabilidad orbital en el espectro de potencias de los datos. Este comportamiento se puede explicar por una evolución cuasi-°©‐cíclica del disco ecuatorial de la estrella acompañante (estrella Be) cuyas características influyen en las condiciones para generar rayos gamma. Estos descubrimientos abren por primera vez la posibilidad de usar observaciones de rayos gamma para estudiar los discos de estrellas masivas en sistemas binarios excéntricos. 2. Estudios de la emisi.n gamma de magnetares a altas y muy altas energ.as con el LAT y con los telescopios Cherenkov MAGIC Los magnetares son una clase particular de estrellas de neutrones que muestran emisión desde radio hasta unos centenares de keV. Se pueden caracterizar por sus explosiones de rayos X y por sus perdidas de energía, las cuales son demasiado pequeñas para justificar su luminosidad en rayos X. Por esta razón, la teoría más aceptada es que la emisión X de la estrella de neutrones está suministrada por el decaimiento y las inestabilidades de sus altos campos magnéticos. En esta tesis, estos objetos han sido estudiados por primera vez a altas y a muy altas energías con el LAT y con los telescopios MAGIC. Hemos impuesto las primeras cotas a la posible emisión gamma de estos objetos. Además, este fuerte diagnóstico observacional fuerza una revisión del espacio de parámetros aplicable a la visibilidad del modelo de “outer gap” de Cheng & Zhang (2001) and Zhang & Cheng (2002) para cada magnetar. 3. Predicciones para la astronom.a Cherenkov con los telescopios CTA La siguiente generación de telescopios Cherenkov será CTA. Este experimento está ahora en la fase de diseño. En esta tesis, evaluamos las capacidades de CTA para estudiar la física no-°©‐térmica de sistemas binarios de rayos gamma. Eso requiere la observación de fenómenos a altas energías a tiempos y a escalas espaciales diferentes. Para hacer eso, hemos estudiado los sistemas binarios de rayos gamma en el contexto de la física conocida o esperada de estas fuentes. CTA será capaz de demostrar los procesos físicos detrás de la emisión gamma en sistemas binarios con una resolución espectral, temporal y espacial alta. Además crecerá el número de fuentes detectadas significativamente. Hemos observado que la sensibilidad de CTA conseguirá un muestreo de curvas de luz y espectros a escalas de tiempo muy cortas de alta calidad. Además, se podrá monitorear fuentes a tiempo largo usando una parte de los telescopios que todavía alcanzará una sensibilidad 2 o 3 veces mayor que cualquier instrumento actual operando a muy altas energías. En particular, es notable que CTA reducirá la indeterminación de los flujos e índices espectrales en unos cuantos factores.
My thesis can be divided into three parts: 1. Study of the gamma-­ray emission of the binary systems LS I +61 303 and LS 5039 at high energies with the Fermi Large Area Telescope (LAT) and the first discovery of superorbital variability at high energies from the source LS I +61 303. Gamma-­‐ray binaries are stellar systems for which the spectral energy distribution (discounting the thermal stellar emission) peaks at high energies. Detected from radio to TeV gamma rays, the gamma-­‐ray binary LS I +61 303 is highly variable across all frequencies. One aspect of this system's variability is the modulation of its emission with the timescale set by the 26.496-­‐day orbital period. In this thesis we show for the first time that the gamma-­‐ray emission of LS I +61 303 also presents a sinusoidal variability at the known superorbital period of 1667 days. This modulation is more prominently seen at orbital phases around apastron, whereas it does not introduce a visible change close to periastron. It is also found in the appearance and disappearance of variability at the orbital period in the power spectrum of the data. This behavior could be explained by a quasi-­‐cyclical evolution of the equatorial outflow of the Be companion star, whose features influence the conditions for generating gamma rays. These findings open for the first time the possibility to use gamma-­‐ray observations to study the outflows of massive stars in eccentric binary systems. 2. Study of the gamma-­ray emission of magnetars at high and very high energies with the LAT and the MAGIC Cherenkov telescopes. Magnetars are a peculiar class of neutron stars showing emission from radio up to some hundreds of keV. They can be characterized through their bursting behavior and through an energy loss rate, which is too small to power their X-­‐ray luminosity. Therefore, it is believed that the X-­‐ray emission of the neutron star is powered by the decay and the instabilities of their strong magnetic field. In this thesis, these objects are studied for the first time at high and very high energies with the LAT and the MAGIC telescopes. We put the first constraints on their emission in this high energy regime. Furthermore, this strong observational diagnostic forces a revision of the parameter space applicable for the viability of the outer gap model of Cheng & Zhang (2001) and Zhang & Cheng (2002) to each magnetar. 3. Prospects for the Cherenkov astronomy with the future Cherenkov Telescope Array (CTA). The next generation of Imaging Air Cherenkov Telescopes will be CTA. This experiment is nowadays in the design phase. In this thesis we evaluate the potentialities of CTA to study the non-­‐thermal physics of gamma-­‐ray binaries, which requires the observation of high-­‐energy phenomena at different time and spatial scales. To do so we study gamma-­‐ray binaries in the context of the known or expected physics of these sources. CTA will be able to probe with high spectral, temporal and spatial resolution the physical processes behind the gamma-­‐ray emission in binaries, significantly increasing as well the number of known sources. We found that the sensitivity of CTA will lead to a very good sampling of light curves and spectra on very short timescales. It will allow as well long source monitoring using subarrays, still with a sensitivity 2–3 times better than any previous instrument operating at VHE energies. In particular, it is noteworthy that CTA will reduce by a factor of a few the errors in the determination of fluxes and spectral indexes.

This thesis describes the analysis of Very High Energy (VHE) emission from the Active Galactic Nucleus PKS 0537-441. It also aims to put the results in a wider context by implementing previous work done on this source. The data chosen for the analysis is provided by the Fermi-LAT satellite and covers the energy range between 300 MeV and 300 GeV. Initially a lightcurve of the received flux from the source was generated, containing data from August 2008 to April 2017, with a mean flux of 4∗10−8 photons per second per squared centimeter. The lightcurve contained sections of different flux intensities giving periods of special interest, such as a flaring period at August 2008 to August 2011, an enormous flare at April 2010 and a less active period between April 2013 - January 2016 that could be identified for further investigations. The differences in observed flux over time was tested and PKS 0537-441 was found to be a significantly variable source. Spectral Energy Distribution (SED) analysis was performed over both the entire period as well as over the selected subperiods and fitted against models using the tools provided by the Fermi Science Support Center (FSSC). The models used in the fitting was PowerLaw2, LogParabola and PLSuperExpCutoff and the best fit for the data was obtained from the PLSuperExpCutoff, except for the less intense period where the LogParabola gave the best fit. The result from the SED analysis was integrated with results from previous work done on the source, ranging over multiple wavelengths in order to get a SED which spanned over the entire electromagnetic spectrum. Finally, modeling of this multi wavelength SED was performed in order to obtain parameters for the physical processes involved in the creation of the radiation received from PKS 0537-441.