Seminars
Our seminars take place in the lecture room of the building at
Praha–Sporilov.
Next seminar:
05.11.2014 15:00
Anastasios Epitropakis
University of Crete
Signals of X-ray reverberation in the AGN "iron-line/continuum" delays
Abstract
Anastasios Epitropakis
Signals of X-ray reverberation in the AGN "iron-line/continuum" delays
X-ray reverberation has been an important tool in constraining the X-ray source geometry and emission mechanism in AGN for more than a decade. With the discovery of the so-called "soft lags" in various AGN starting with 1H 0707-495 in 2009, their interpretation as "light echoes" from a hot disc of illuminated material orbiting close to a super-massive black hole has opened a new realm of possibilities for putting tight constraints on the X-ray continuum/reflector geometry. Contemporary works have shifted their attention to the study of delays between the X-ray continuum and the broad iron-line (~5-7 keV), observed in the X-ray spectra of several AGN, whose strength and shape makes it the best available candidate for having a clear reflection origin. In this talk I will discuss and present the latest results of the work that I have been doing as part of my PhD thesis regarding the study of these so-called "iron-line/continuum" delays.
15.12.2014 10:30
Jan Cechura
Astronomical Institute, Academy of Sciences, Prague
Physics of X-ray binaries
Abstract
Jan Cechura
Physics of X-ray binaries
We present a novel observation interpreting method for the high-mass X-ray binaries (HMXBs) based on a combination of spectroscopic data and numerical results of a radiation hydrodynamic model of stellar wind in HMXBs. By using an indirect imaging method of Doppler tomography, we calculate synthetic tomograms of a predicted emission in Low/Hard and High/Soft X-ray states and compare them with tomograms produced using phase-resolved optical spectra of Cygnus X-1, a prototype of HMXBs. The emissions of HMXBs are determined by the local conditions within the circumstellar medium - namely by local density, temperature, and ionization parameter. These quantities are computed by the radiation hydrodynamic code and strongly depend on the X-ray state of such systems. By increasing intensity of an X-ray emission produced by the compact companion in the HMXB-model, we achieved a complete redistribution of the circumstellar medium in the vicinity of the modelled system. These changes (which simulate the transitions between two major spectral states) are also apparent in the synthetic Doppler tomograms which are in a good agreement with the observational data.
16.12.2014 16:00
Chris Done
University of Durham, United Kingdom
The disc-spin-jet connection in stellar and supermassive black holes
Abstract
Chris Done
The disc-spin-jet connection in stellar and supermassive black holes
Black hole spin is difficult to measure as it leaves an imprint only close to the horizon, but it may be required to produce most dramatic relativistic jets seen in the flat spectrum radio quasars (FRII) and BL Lacs (FRI). I will review what we know about the connection between the accretion flow, jet and spin in the stellar mass black hole binary systems and then scale this up to the supermassive black holes in AGN and quasars, including spin constraints from the new techniques which use fast variability to reverberation map the inner disc.
Previous seminar:
17.10.2014 09:20
Jaroslav Hamersky
Astronomical Institute, Academy of Sciences, Prague
Triggered oscillations and destruction of magnetized relativistic tori in 2D
Abstract
Jaroslav Hamersky
Triggered oscillations and destruction of magnetized relativistic tori in 2D
Runaway instability operates in accretion tori around black holes, where it affects systems close to the critical (cusp overflowing) configuration. The runaway effect depends on the radial profile l(R) of the angular momentum distribution of the fluid, on the dimension-less spin a of the central black hole (|a| ≤ 1), and other factors, such as self-gravity. Here we discuss the role of runaway instability within a framework of an axially symmetric model of perfect fluid endowed with a purely toroidal magnetic field. Talked based on a recent contribution in Proceedings of the International Astronomical Union, Volume 303, pp. 424-426.
If you would like to give a seminar in our group, please contact Vladimir Karas or Jaroslav Hamersky.
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