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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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