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Dark matter
Vraštil, Michal ; Mészáros, Attila (advisor) ; Heyrovský, David (referee)
The dark matter constituting approximately 85% of the mass is an integral part of our universe. As many astronomical observations at different scales of space so the theoretical models show that there is more matter than we can see directly. This overview describes the major historical events and observational data from the time of Zwicky to the present leading to today's view on the dark matter. The paper further describes the cosmological implications of the presence of dark matter - its impact on the formation of structures in the universe and reflection of fluctuations in the cosmic background radiation. Here I describe possible candidates for dark matter - a small contribution of baryonic matter and the main candidates among non-baryonic matter. In addition to possible new particles explaining the missing mass I describe alternatives to the theory of gravity, which do not require any extra matter, in particular, I deal with a very successful theory of MOND. At the end I mention a brief overview of today's possibilities of direct or indirect observation of dark matter.
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Studium negaussovských světelných křivek pomocí Karhunenova-Loveho rozvoje
Greškovič, Peter ; Pecháček, Tomáš (advisor) ; Mészáros, Attila (referee)
We present an innovative Bayesian method for estimation of statistical parameters of time series data. This method works by comparing coefficients of Karhunen-Lo\`{e}ve expansion of observed and synthetic data with known parameters. We show one new method for generating synthetic data with prescribed properties and we demonstrate on a numerical example how this method can be used for estimation of physically interesting features in power spectra calculated from observed light curves of some X-ray sources.
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Statistical Analysis of the Observable Data of Gamma-Ray Bursts
Řípa, Jakub ; Mészáros, Attila (advisor)
Gamma-ray bursts are still not fully understood events. However, their exploration could pro- vide a useful tool for a better understanding of the early Universe because they belong to the most distant and violent objects that astronomers know. This thesis tries to bring more information about a so-called group of intermediate-duration bursts claimed by different authors employing dif- ferent data samples. Firstly, duration and spectral hardness properties of bursts from the Reuven Ramaty High-Energy Solar Spectroscopic Imager are statistically analysed. The obtained results bring a suspicion that these intermediate bursts gather into a separate group. Secondly, these bursts are investigated in more detail with respect to their spectral lags, peak count rates, red- shifts, supernova observations, and so forth. Thirdly, long-duration bursts with known redshifts and with derived pseudo-redshifts detected by The Burst and Transient Source Experiment, Swift and Fermi bursts with known redshifts, are used to study the cosmological effects on the observed flux and fluence distributions.
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Statistical Analysis of the Observable Data of Gamma-Ray Bursts
Řípa, Jakub ; Mészáros, Attila (advisor) ; Münz, Filip (referee) ; Ramirez-Ruiz, Enrico Jorge (referee)
Gamma-ray bursts are still not fully understood events. However, their exploration could pro- vide a useful tool for a better understanding of the early Universe because they belong to the most distant and violent objects that astronomers know. This thesis tries to bring more information about a so-called group of intermediate-duration bursts claimed by different authors employing dif- ferent data samples. Firstly, duration and spectral hardness properties of bursts from the Reuven Ramaty High-Energy Solar Spectroscopic Imager are statistically analysed. The obtained results bring a suspicion that these intermediate bursts gather into a separate group. Secondly, these bursts are investigated in more detail with respect to their spectral lags, peak count rates, red- shifts, supernova observations, and so forth. Thirdly, long-duration bursts with known redshifts and with derived pseudo-redshifts detected by The Burst and Transient Source Experiment, Swift and Fermi bursts with known redshifts, are used to study the cosmological effects on the observed flux and fluence distributions.
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Statistical analysis of the gamma-ray bursts satellite data
Bystřický, Pavel ; Mészáros, Attila (advisor) ; Brož, Miroslav (referee)
In this thesis the Gamma-Ray Bursts (GRBs) are studied, the brightest explosions in the universe. GRBs have been observed since year 1967, but there are several unsolved problems. In the first chapter there is an introduction to the issue of GRBs, and the history of observations are briefly described. The Fermi satellite, the latest satellite devoted to gamma-ray burst observations is described in chapter two. Characteristics of the Fermi instruments are also described. The observed data of GRBs are characterized in the third chapter. The distribution of GRB durations, distances, and spectral hardnesses are described. The characteristics of long and short GRBs (distance, isotropy of distribution, metalicity dependence, isotropic energy) are described. A chance of the appearance of a GRB in the Milky Way is discussed. New Fermi observations are described too. Fourth chapter is about models of GRBs. The fireball and canonball models are described. Fifth chapter is focused on the exposure function of CGRO-BATSE, Fermi-GBM, Swift. I have created the exposure function for GBM on Fermi satellite. It is quite difficult, and I have assumed some simplified hypotheses. Information of the satellite's position, position of detectors on the Fermi satellite, have been found on the Fermi web pages and in the article...
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Determinating the cosmological omega factors with supernovae Ia
Rieb, Tomáš ; Jungwiert, Bruno (referee) ; Mészáros, Attila (advisor)
My thesis is an attempt to determine cosmological omega factors using the data measured during observations of the supernovae type Ia with cosmological redshift z 0,1. For the determination of omega factors I use the method of fi tting measured data in Hubble s diagram. I evaluate the ts by the 2-tests. The values of omega factors, coming out of the analyses as the most probable ones di ffer from the results which are published in the contemporary scienti c literature. The question which I am posing is, if it is correct to reject the cosmological models with a zero value of the cosmological constant. At the first sight statistical results of 2-test, which issue from my thesis, seem to be su fficient enough to reject these models. But the denial of the zero cosmological constant appears as ambivalent by detailed analysis of the occasions and reasons for it. As the basis for my analyses, I use the data collected by a number of scientifi c teams. I cannot succesfully fi t most of these data, because the dispersions of their positions in Hubble s diagrams are too large. I can conclude that the observations of the supernovae Ia alone are not satisfactory for a reliable determination of the cosmological omega factors.
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The study of gamma-ray bursts detected by satellite RHESSI
Řípa, Jakub ; Mészáros, Attila (advisor) ; Karas, Vladimír (referee)
The beginning of the theoretical section of this diploma thesis is pointed to a discovery of the gamma-ray bursts. Then it is pointed to a brief historical summary of the different instruments dedicated to the GRB's field. Because the main aim of this work is the basic analysis and the classifying of the observed gamma-ray bursts by RHESSI solar satellite (which has observed more than 220 GRBs yet), a technical description of this instrument is introduced. It is followed by a part about gamma-ray production mechanisms. In this work there are also mentioned some related gamma-ray sources e.g. SGRs. The theoretical résumé is concluded by the description of the GRB's afterglows and some preferred models of their origins. In the proper study there was done the morphological classifying of the GRB's temporal profiles. Next there was studied the duration distribution with orientation to determine number of the subclasses using lognormal fits and the 2 test. Distribution of the radial distances of the gamma-ray sources can be examined by the log N vs. log P. dependence. The results are properly discussed and compared with the results of the BATSE instrument (including the V/Vmax test). In the final stage of this work, there is argued the dependence between the hardness ratios and the durations.
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On the Friedmann equation for the three-dimensional hypersphere
Křížek, Michal ; Mészáros, A.
The present standard cosmological model of the evolution of our universe, is based on the Friedmann equation, which was published by Alexander Friedmann in 1922. He applied Einstein’s equations to an expanding threedimensional sphere which enabled him to avoid boundary conditions. However, his description was very brief. Therefore, the main objective of this article is to detailed a derivation of the Friedmann equation for an unknown expansion function a = a(t) representing the radius of the universe. Furthermore, we present serious arguments showing why the validity of Einstein’s equations should not be extrapolated to the entire universe.
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