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Akademie věd České republiky |
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Akademie věd České republiky |
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Pravidelný seminář 3. 4. 2006
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který se koná v pondělí dne v zasedací místnosti Kosmické laboratoře AsÚ v Ondřejově PROGRAM: 13:00 odborná část V odborné části vyslechneme informace z oddělení 'Galaxie a
planetární soustavy': 1. Novinky z oddělení (Jan Palouš) High-frequency quasiperiodic oscillations in accretion discs Michal Bursa A new unique kind of X-ray signal modulation – so called quasi-periodic oscillations, QPOs – was detected at frequencies 1-50 Hz in early 1980s during observations of X-ray emission from several Galactic low-mass X-ray binary sources. During the time different types of QPOs were found in many sources in the Milky Way, characterised by a specific shape and frequency range. The most striking, the most interesting and undoubtedly the most mysterious type of QPOs are so-called high-frequency quasi-periodic oscillations (HFQPOs), which appear in the range of frequencies that Keplerian orbits very close to compact stars would have (200-1300 Hz). I will discuss main highlights of a decade of the HFQPO research, focusing namely on similarities and differences between HFQPOs properties in black hole and neutron star sources, scaling of frequencies with mass, correlations and anti-correlations in QPO data, theoretical interpretations, and possible mechanisms for the signal modulation. I will also summarize results of my Thesis that suggest the origin of high-frequency QPOs may be found in the presence of a toroidal advection-dominated type of an accretion flow close to the marginally stable orbit. Srdečně zve Vladimír Karas vedoucí semináře |