Relativistický seminář
Ústavu teoretické fyziky


Seminář se koná v úterý ve 13:10 v posluchárně ÚTF MFF UK
v 10. patře katedrové budovy v Tróji, V Holešovičkách 2, Praha 8


Příští semináře:

26. října 2021
Zoom talk, https://cuni-cz.zoom.us/j/9988276224?pwd=VGF5ZUFKMFVBTEx2QnAxQkxZSWhLdz09
Polarisation of reflected X-ray emission from accretion discs in Active Galactic Nuclei
Jakub Podgorný
Astronomical Institute of the Czech Academy of Sciences, Ondřejov/Spořilov
(seminář v angličtině)

We present the theoretical spectrum and polarisation properties of X-ray emission from accretion discs in active galactic nuclei (AGN) including relativistic effects. The reflected radiation from an accretion disc illuminated by a hot corona above is computed using the Monte Carlo radiative transfer code STOKES. The structure of the disc, modelled as a constant density slab, has been computed with the code for optically thick and hot photo-ionized media TITAN. The resulting simulated spectra locally emitted by the accretion disc in 0.1–100 keV energy band are compared to the results obtained by various, published radiative transfer codes. In addition to these, the STOKES code also provides the polarisation degree and polarisation angle of the outcoming radiation that depend on the geometry of scattering and other key parameters such as the ionisation of the disc. Further, we use the relativistic code KYNSTOKES to account for relativistic effects on radiation near a black hole and to compute the total disc emission as would be detected by a distant observer. In this way it is then possible to predict X-ray spectral and polarisation properties of an accretion disc in AGN and their dependence on various parameters of the system (spin of the black hole, geometry of the corona, ionization of the accretion disc, observer inclination). This is fundamental for the interpretation of AGN spectra and polarisation obtained by the upcoming X-ray polarimetric missions, such as NASA IXPE mission or Chinese-lead eXTP mission.

5. listopadu 2021
!!! FRIDAY !!! from 13:10 (no seminar on Tuesday this week)
Parametrization of black-hole spacetimes and the Blandford-Znajek mechanism for the general slowly rotating black holes
Dr. Roman Konoplya
Research Centre for Theoretical Physics and Astrophysics, Institute of Physics, Silesian University in Opava
(seminář v angličtině)

We will briefly review the general parametrization of the axially symmetric black hole spacetime, which is similar in spirit to the parametrized post-Newtonian approximation, but valid in the whole space outside the event horizon, including the near horizon region. Then, we consider the Blandford-Znajek process of electromagnetic extraction of energy from a general axially symmetric asymptotically flat slowly rotating black hole given in the parametrized form. Using the general parametrization of the black-hole spacetime we construct formulas for the flux of the magnetic field and the rate of energy extraction, which are valid not only for the Kerr spacetime, but also for its arbitrary axially symmetric deformations. We show that in the dominant order these quantities depend only on a single deformation parameter, which relates the spin frequency of a black hole with its rotation parameter.


Minulé semináře:

12. října 2021
Universality of curvature invariants in critical vacuum gravitational collapse
Tomáš Ledvinka, Anton Khirnov
ÚTF
(seminář v angličtině)
We consider several families of asymptotically flat initial data which, similar to the well-known Choptuik's discovery, can be fine-tuned between dispersal into empty space and collapse into a black hole. We discuss the applied methods and then we show that near-critical spacetimes exhibit behavior similar to scalar-field collapse: For different families of initial data, we observe universal "echoes" in the form of irregularly repeating, approximate, scaled copies of the same piece of spacetime.

Záznam:
19. října 2021
General Relativity on AdS_3 and the AKNS hierarchy
Kristiansen Lara
Department of Physics, University of Santiago de Chile
(seminář v angličtině)
It is shown that the Ablowitz-Kaup-Newell-Segur (AKNS) integrable hierarchy can be obtained as the dynamical equations of three-dimensional General Relativity with a negative cosmological constant. This geometrization of AKNS system is possible through the construction of novel boundary conditions for the gravitational field. These are invariant under an asymptotic symmetry group characterized by an infinite set of AKNS commuting conserved charges. Gravitational configurations are studied by means of SL(2,R) conjugacy classes. Conical singularities and black hole solutions are included in the boundary conditions.

Záznam:

Předchozí ročníky:


Jiří Bičák                                                                                                  Oldřich Semerák


© 21. října 2021; Oldřich Semerák <semerak@mbox.troja.mff.cuni.cz>
© 26. října 2021; vygenerováno pomocí aplikace seminar, verze 2.04 (2003-09-02); správce <Pavel.Krtous@utf.mff.cuni.cz>