20240125 22:11 
Can extended bodies follow geodesic trajectories?
LukesGerakopoulos, Georgios ; Mukherjee, Sajal
We provide an extension of the analysis on whether an extended test body can follow a geodesic trajectory given by Mukherjee et al. (2022). In particular, we consider a test body in a poledipolequadrupole approximation under the OhashiKyrianSemer´ak spin supplementary condition moving in the Schwarzschild and Kerr background. Using orbital setups under which a poledipole body can follow geodesic motion, we explore under which conditions this can also take place in the poledipolequadrupole approximation when only the mass quadrupole is taken into account. For our analysis, we employ the assumption that the dipole contribution and the quadrupole contribution vanish independentlly.
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20240125 22:11 
Growth of orbital resonances around a black hole surrounded by matter
Stratený, Michal ; LukesGerakopoulos, Georgios
This work studies the dynamics of geodesic motion within a curved spacetime around a Schwarzschild black hole, perturbed by a gravitational field of a far axisymmetric distribution of mass enclosing the system. This spacetime can serve as a versatile model for a diverse range of astrophysical scenarios and, in particular, for extreme mass ratio inspirals as in our work. We show that the system is nonintegrable by employing Poincaré surface of section and rotation numbers. By utilising the rotation numbers, the widths of resonances are calculated, which are then used in establishing the relation between the underlying perturbation parameter driving the system from integrability and the quadrupole parameter characterising the perturbed metric. This relation allows us to estimate the phase shift caused by the resonance during an inspiral.
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20240125 22:11 
Astrophysical black holes embedded in organized magnetic fields
Karas, Vladimír
Largescale magnetic fields pervade the cosmic environment where the astrophysical black holes are often embedded and influenced by mutual interaction. In thiscontribution, we outline the appropriate mathematical framework to describe magnetized black holes within General Relativity, and we show several examples of how these can be employed in the astrophysical context. In particular, we examine the magnetized black hole metric in terms of an exact solution of electrovacuum EinsteinMaxwell equations under the influence of a nonvanishing electric charge. New effects emerge: the expulsion of the magnetic flux out of the blackhole horizon depends on the intensity of the imposed magnetic field.
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20240125 22:11 
MAD UFOs: Magnetically Arrested Discs with persistent UltraFast Outflows
Suková, Petra ; Zajaček, M. ; Karas, Vladimír
We study an outflow that develops in the MAD state in 3D GRMHD simulations. We show that the outflow can be accelerated to\nrelativistic velocities and persist over the course of our simulation. We compare the properties of the outflow from MAD discs with those launched by orbiting secondary at close orbit. The main difference is that the orbiting body launches a more coherent, quasiperiodic ultrafast outflow at lower velocities (v < 0.5c) while the outflow launched in the MAD state (without the body) has a stochastic behaviour and has anapproximately flat velocity distribution between lower anf higher outflow velocities, 0.2c < v < 0.3c and v > 0.5c.
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20210224 00:43 
Understanding the iron K alpha line emissivity profile with GR radiative transfer code
Zhang, Wenda ; Dovčiak, Michal ; Bursa, Michal ; Svoboda, Jiří ; Karas, Vladimír
In this work, we present calculations of the illumination and the iron K alpha emissivity profiles performed with the GR radiative transfer code Monk that employs the Monte Carlo method. In most previous studies the distinction between the illumination and emissivity profiles was not clearly made. For AGN discs, the emissivity profile has a similar shape with the illumination profile, but in the inner most region the former is steeper than the latter, where as for accretion discs in black hole Xray binaries, the distinction between the two profiles is more dramatic. We find out that the different behavior between AGN and black hole Xray binary discs is due to the different energy spectra of the illuminating radiation. This suggests that the emissivity profile of the iron Kαline cannot be determined by black hole spin and corona geometry alone and the energy spectrum of the illuminating radiation has to be taken into account. We also study the dependence of the emissivity profile on the geometry of the corona.
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20210224 00:43 
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20210224 00:43 
Missing bright red giants in the Galactic center: A fingerprint of its once active state?
Zajaček, Michal ; Araudo, Anabella ; Karas, Vladimír ; Czerny, B. ; Eckart, A. ; Suková, Petra ; Štolc, Marcel ; Witzany, V.
We propose a novel scenario for the bright redgiant depletion based onthe collisions between red giants and the nuclear jet, which was likely active in the Galactic center a few million years ago and could have led to the formation of the largescaleγray Fermi bubbles. The process of the jetinduced ablation of red giants appears to be most efficient within∼0.04 pc(Scluster), while at larger distances it was complemented by star–accretion disc collisions and at smaller scales, tidal stripping operated. These three mechanisms likely operated simultaneously and createdan apparent core of latetype stars within∼0.5 pc.
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20210224 00:43 
Perturbing the accretion flow onto a supermassive black hole by a passing star
Suková, Petra ; Zajaček, M. ; Witzany, V. ; Karas, Vladimír
The close neighbourhood of a supermassive black hole contains not only accreting gas and dust, but also stellarsized objects like stars, stellarmass black holes, neutron stars, and dustenshrouded objects that altogether form a dense nuclear starcluster.These objects interact with the accreting medium and they perturb the otherwise quasistationary configuration of the accretion flow. We investigate how the passages of a star can influence the black hole gaseous environment with GRMHD 2D and3D simulations. We focus on the changes in the accretion rate and the associated emergence of outflowing blobs of plasma.
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20210224 00:43 
From gappy to ringed: signatures of an accretion disk radial structure in profiles of the reflection line
Štolc, Marcel ; Zajaček, M. ; Karas, Vladimír
We focus on the theoretical profiles of a spectral line produced by reflection of the surface of both gappy accretion disk and a ringlike structure near a black hole. We describe the relativistic effects in an approximative manner. While a smooth accretion disk leads to a typical, doublehorn shape with unequal wings due to Doppler boosting and an additional peak due to the lensing amplification at high inclination angle, the gaps and rings give rise to a more complex dependence which reflects the location and the radial extent of the inhomogeneities in the accretion flow.
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20210224 00:43 
On maximum energy cutoff in the hotspot of radiogalaxies 3C 105 and 3C 445
Pulnova, Y. ; Araudo, Anabella
The origin of UltraHighEnergy Cosmic Rays is still unknown, and Active Galactic Nuclei have been proposed as candidates to accelerate these particles. Using thewellresolved radio emission from radiogalaxies 3C 105 and 3C 445 we investigate the standard assumption that the distribution of nonthermal electrons has a maximum energy cutoff due to the synchrotron cooling. We show that as a consequence this would lead to an unphysically large number density in the hotspot. This result has important implications for the origin of UltraHighEnergy Cosmic Rays.
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