Seminars
Our seminars take place in the lecture room of the building at
Praha–Sporilov.
Next seminar:
22.06.2017 14:00
Abigail Stevens
Anton Pannekoek Institute for Astronomy, University of Amsterdam, The Netherlands
Comparing origins of low-frequency quasi-periodic oscillations with spectral-timing
Abstract
Abigail Stevens
Comparing origins of low-frequency quasi-periodic oscillations with spectral-timing
X-ray spectral-timing is a new field that seeks to investigate how matter behaves in strong gravitational fields. Observations suggest that different types of low-frequency quasi-periodic oscillations (QPOs) are associated with different emitting-region geometries (e.g., disk-like or jet-like) in the innermost part of the X-ray binary, close to the neutron star or black hole. We developed a technique for phase-resolved spectroscopy of QPOs, and are applying it to Type B and Type C low-frequency QPOs from the black hole X-ray binary GX 339-4. On the QPO time-scale, we find that the energy spectrum changes not only in normalization, but also in spectral shape. We can quantify how the spectral shape changes as a function of QPO phase, and the two different QPOs show markedly different spectral changes. In our previous work, we inferred that the Type B QPO could be caused by a large-scale-height (i.e., jet-like) precessing region illuminating and heating overlapping azimuthal regions of the inner accretion disk. Preliminary results of the Type C QPO indicate that a small-scale-height (disk-like) precessing region may be responsible for the observed spectral changes. This talk will feature results from this paper: https://ui.adsabs.harvard.edu/#abs/2016MNRAS.460.2796S/abstract
Previous seminar:
29.05.2017 14:00
Vojtěch Witzany
ZARM, University Bremen, Am Falturm 2, 28359 Bremen, Germany
Generalized conservation law near spinning black holes
Abstract
Vojtěch Witzany
Generalized conservation law near spinning black holes
Conservation of energy and angular-momentum fluxes is a well known property of the evolution of any matter field in any axisymmetric stationary metric. However, there is another flux corresponding to the „hidden symmetry“ of the Kerr space-time undergoing well-defined evolution which can be understood as a generalized conservation law. In this talk I derive the flux and its properties and discuss applications to simulations of accretion onto black holes.
If you would like to give a seminar in our group, please contact Petra Sukova or Vladimir Karas.
Archive
2017,
2016,
2015,
2014,
2013,
2012,
2011,
2010,
2009,
2008,
2007,
2006,
2005,
2004