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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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Infrared-excess Source DSO/G2 Near the Galactic Center: Theory vs. Observations
Zajaček, M. ; Eckart, A. ; Peissker, F. ; Karssen, G. ; Karas, Vladimír
Based on the monitoring of the Dusty S-cluster Object (DSO/G2) during its closest approach to the Galactic Center supermassive black hole in 2014 and 2015 with ESO VLT/SINFONI, we further explore the model of a young, accreting star to explain observed spectral and morphological features. The stellar scenario is supported by our ndings, i.e., ionized-hydrogen emission from the DSO that remains spatially compact before and after the peribothron passage. The detection of DSO/G2 object as a compact single-peak emission-line source is not consistent with the original hypothesis of a core-less cloud that is necessarily tidally stretched, hence producing a double-peak emission line prole around the pericentre passage. This strengthens the evidence that the DSO/G2 source is a dust-enshrouded young star that appears to be in an accretion phase. The infall of material from the circumstellar disc onto the stellar surface can contribute signicantly to the emission of Br line as well as the observed large line width of the order of 10 angstrom.
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