Orientador: Rogério Rosenfeld / Banca: Reuven Opher / Banca: Adriano Antônio Natale / Resumo: A origem dos raios cósmicos de altíssimas energias (RCAE's) é uma das maiores questões em aberto na astrofísica. Um dos modelos propostos para explicar estes eventos sugere que eles sejam produtos do decaimento de partículas metaestáveis supermassivas, as quais chamamos partículas X. Estas partículas, que seriam uma fração da matéria escura fria no Universo, podem ser produzidas no período de reaquecimento após a fase inflacionária no Universo primordial. Estudamos esta possibilidade e, a partir do fluxo detectado de RCAE's, obtivemos limites para alguns parâmetros como a meia vida e a razão de ramificação para o decaimento direto do inflaton em partículas X / Abstract: The origin of ultra high energy cosmic rays (UHECR's) is one of the major unresolved questions in astrophysics. One of the models proposed to explain these events suggests that they are the decay products of supermassive metastable particles, which we call X particles. These particles can be produced in the reheating period following the inflationary epoch of the early Universe and they would be a fraction of cold dark matter. We study this possibility and obtain constraints on some parameters such as the lifetime and branching ratio for the direct decay of the inflaton to X-particIes, from the requirement that they are responsible for the observed UHECR flux / Mestre

Orientador: Anderson Campos Fauth / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-15T00:09:48Z (GMT). No. of bitstreams: 1 Tavares_DenisBorgarelli_M.pdf: 5623442 bytes, checksum: 17583c9607ed6e94cf631816f4ccb01f (MD5) Previous issue date: 2010 / Resumo: Um dos fenômenos previstos por Einstein na dedução da relatividade geral foi a existência de pequenas perturbações da métrica que ele nomeou de ondas gravitacionais.Essas ondas ao atravessarem a matéria fazem com que a mesma oscile de acordo com a polarização da onda gravitacional.Esta é a única previsão importante da Relatividade Geral que ainda não foi comprovada completamente.O pequeno sinal gerado pela passagem de uma onda gravitacional em comparação com os ruídos existentes no sistema de detecção torna a sua detecção direta um dos principais desafios da ciência moderna.Neste trabalho estudamos o ruído gerado por raios cósmicos na antena gravitacional Mario Schenberg,localizada na cidade de São Paulo.Medidas do fluxo de múons e hádrons isolados realizadas no hemisfério norte foram utilizadas para calcular o fluxo esperado dessas partículas na cidade de São Paulo.O cálculo da energia depositada no detector de ondas gravitacionais pelos raios cósmicos foi realizado através de simulações de Monte arlo utilizando o Geant4.A passagem de múons e prótons,com diversas energias e alguns ângulos de incidência,pelo prédio e pela esfera ressonante da antena gravitacional,foi simulada.Desenvolvemos um modelo termo-acústico, denominado de multiponto,adequado para calcular as energias depositadas nos modos normais de vibração da esfera a partir da energia depositada na esfera por partículas elementares.om esses resultados calculamos a taxa esperada de sinal de raios cósmicos no principal modo de detecção de ondas gravitacionais,nl=12,do detector Mario Schenberg para temperaturas de operação Tnoise entre 10 -5 e 10 -7 K.Os resultados obtidos mostraram que para a sensibilidade projetada para 4,2K do detector Mário Schenberg a taxa de sinais devido aos raios cósmicos é muito pequena,sendo da ordem de 5 eventos por dia.Porém,quando for atingido o limite quântico,será preciso uma análise mais detalhada do sinal de saída da antena,já que o número de partículas esperado aumenta consideravelmente, alcançando cerca de 250 sinais por dia / Abstract: One of the phenomena predicted by Einstein in the derivation of general relativity is the existence of small perturbations of the metric that he named gravitational waves.As they travel through space oscillates the space-time according to its polarization.This is the only major prediction of general relativity not yet proven completely.The small signal generated by the passage of a gravitational wave compared to the noise in the system of detection makes their direct detection one challenge of modern science.In this paper we study the noise generated by cosmic rays in the gravitational antenna Mario Schenberg,located in the city of Sao Paulo.Single muons and hadrons flux measurements held in the northern hemisphere were used to calculate the expected flux of these particles in the city of Sao Paulo. The calculation of the energy deposited in the detector of gravitational waves from cosmic rays was performed by Monte arlo simulations using Geant4.The transport of muons and protons,with several energy and some different angles of incidence,across the building and the resonant sphere was simulated.We developed a thermo-acoustic model,called multi-point,suitable for calculating the energy deposited in the normal modes from the energy deposited on the sphere by elementary particles. With these results we calculate the expected rate of cosmic ray signals in the main detection mode of gravitational waves,nl =12,of the Mario Schenberg detector,for temperatures Tnoise between 10 -5 and 10 -7 K.The results showed for the designed for 4.2 K sensitivity of the Mario Schenberg detector that the rate of signals due to cosmic rays is very small,being around 5 events per day.However,when it will reach the quantum limit will be needed a more detailed analysis of the antenna signal output,since the expected number of cosmic ray noise increases considerably,reaching about 250 signals per day / Mestrado / Física das Particulas Elementares e Campos / Mestre em Física

We develop a simple one-zone model of the steady-state Crab nebula spectrum encompassing both the radio/soft X-ray and the GeV/multi-TeV observations. By solving the transport equation for GeV-TeV electrons injected at the wind termination shock as a log-parabola momentum distribution and evolved via energy losses, we determine analytically the resulting differential energy spectrum of photons. We find an impressive agreement with the observed spectrum of synchrotron emission, and the synchrotron self-Compton component reproduces the previously unexplained broad 200-GeV peak that matches the Fermi/Large Area Telescope (LAT) data beyond 1 GeV with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) data. We determine the parameters of the single log-parabola electron injection distribution, in contrast with multiple broken power-law electron spectra proposed in the literature. The resulting photon differential spectrum provides a natural interpretation of the deviation from power law customarily fitted with empirical multiple broken power laws. Our model can be applied to the radio-to-multi-TeV spectrum of a variety of astrophysical outflows, including pulsar wind nebulae and supernova remnants, as well as to interplanetary shocks.

A basket weaving technique for making radio continuum maps has been developed at the Hartebeesthoek Radio Astronomy Observatory (HartRAO). This data reduction technique significantly reduces scanning effects by using independent maps scanned in orthogonal directions. The observation and data analysis procedures that were developed are presented. The technique was used to map the supernova remnant MSH 15-52 at frequencies of 5000 MHz and 8500 MHz. The flux spectral index for this supernova remnant was found to be 0.83 ± 0.02 in this frequency range. Two regions (A and B) of the Galactic plane were observed at 8500 MHz with a resolution of 6'. Region A covered the 5°x5° area 47.5°< k 52.5°, Ibl < 2.5°, and region B was the 4.2°x3° area 320.4°< I <334.6°, Ibl < 1.5°. Far infrared observations at 60 !lm were used in conjunction with the radio maps to separate the thermal and non-thermal components of the radio emission. The technique can be used to map the Galactic plane at 8500 MHz using dual polarisation once the receiver at HartRAO has been upgraded. This would fulfil a need for a medium resolution, high frequency survey of the southern Galactic plane. / Adobe Acrobat Pro 9.4.6 / Adobe Acrobat 9.46 Paper Capture Plug-in

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The Earth’s upper atmosphere is suffused by radiation caused primarily by a bombardment of Cosmic Rays, as a result of which it is hazardous for human beings as well as sensitive electronic equipment on board flight vehicles. A series of ground based as well as airborne experiments were performed using Polylactic Acid (PLA), Acrylonitrile-Butadiene-Styrene (ABS) and High Impact Polystyrene (HIPS), in order to investigate the applicability of polymers that can meet today’s needs for lightweight, multifunctional, and cost efficiency in radiation shielding of electronic equipment. It was found that PLA at 8 mm thickness has an effectiveness of 66% against gamma radiation (i.e., it blocked 66% of the gamma radiation). Therefore, it was decided to proceed with a high altitude balloon experiment with an 8 mm thickness of PLA. The shield was demonstrated to be reasonably effective in attenuating radiation from cosmic rays.

<p>Astrophysical jets are collimated streams of magnetized plasma launched from compact objects, such as neutron stars or black holes. These jets, powered by the accretion of surrounding gas onto the compact object, can accelerate particles to extreme energies and produce powerful radiation.</p> <p><br></p> <p>In this report, I investigate energy dissipation and particle acceleration in two key regions in jets: (i) external shocks which form where jets interact with ambient gas and (ii) internally in the jet where particles are likely to be energized through the process of magnetic reconnection.</p> <p><br></p> <p>First, I explore inverse Compton scatterings of electrons accelerated at the external shock as a candidate for the high energy emissions from gamma-ray burst afterglows. I consider two sources of seed photons for scattering: synchrotron photons from the blast wave (synchrotron self-Compton) and photon fields external to the shock (external Compton) from the star-forming region in the host galaxy. I develop an analytical model to predict the high-energy spectra from these blasts and reproduce the observed spectra and lightcurves of GRB~190114C. The model implies that inverse Compton can dominate the sub-TeV/TeV emission in this event.</p> <p><br></p> <p>Second, I study the particle acceleration mechanism of magnetic reconnection internally in astrophysical jets. I employ particle-in-cell (PIC) simulations of 3D relativistic magnetic reconnection. My analysis reveals a novel acceleration mechanism that only operates in 3D that results in faster particle acceleration. Unlike in 2D simulations where particles are trapped in the reconnected plasma and stop being accelerated, a fraction of particles in 3D can escape from this region (along the third direction) and be further accelerated. The escaped particles are characterized by a harder energy spectrum with a higher cutoff compared to those found in previous studies. Based on the PIC simulation findings, I build an analytical model for the particle kinetics, which divides particles into two groups --- one undergoing fast energization in the reconnection upstream region and the other residing in the reconnected plasma without energy change. The model predicts a power-law spectra for both groups of particles. PIC simulations reveal a universal magnetization-independent spectra with $dN/d\gamma\propto \gamma^{-2}$ for the overall particle population. The results demonstrate that relativistic reconnection in jets may be a promising mechanism for generating Ultra-High-energy Cosmic Rays. </p>

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