Seminars 2014
03.07.2014 15:00
Abhijeets Borkar
I. Institute of Physics, University of Cologne, Germany
Monitoring the Galactic Center with ATCA
Abstract
Abhijeets Borkar
Monitoring the Galactic Center with ATCA
The center of the Milky Way hosts a highly variable radio, NIR
& X-ray source, Sagittarius A* (Sgr A*) which is associated with a 4
million solar mass super-massive black hole (SMBH). Sgr A* is known to
have a flaring activity occurring from a few hours to few days which has
been observed at X-ray and NIR wavelengths with radio/sub-mm flare
following approximately 100 min later. This suggests that Sgr A*
undergoes accretion events sporadically. To study the underlying
mechanism of the flaring of Sgr A*, we have observed the Galactic Center
with ATCA. In this talk, I will present the first results of these
observations of the GC.
26.06.2014 17:00
Naresh Dadhich
Centre for Theoretical Physics, Delhi
Einstein's Relativity For Everyone
Abstract
Naresh Dadhich
Einstein's Relativity For Everyone
Prof Dadhich will give a talk on “Einstein For Everyone”, accessible to people of all backgrounds including non-scientists. His lecture has been designed to convey the basic message of Einstein’s Relativity in non-technical terms using purely common sense arguments.
Přednášku uvede Prof. J. Bičák, v případě zájmu ji bude překládat do češtiny.
24.06.2014 14:00
William Alston1, Erin Kara1, and Michal Dovciak2
(1) Institute of Astronomy, University of Cambridge; (2) Astronomical Institute, Academy of Sciences, Prague
X-ray echos from Active Galactic Nuclei
Abstract
William Alston1, Erin Kara1, and Michal Dovciak2
X-ray echos from Active Galactic Nuclei
Recently, time lags between hard and soft X-ray band emission in AGN
have been observed by X-ray observatory XMM-Newton. These may be
naturally interpreted as the delays between the intrinsic fluctuations
in corona that emits primary power-law radiation and their reflection
from the accretion disc below. In this talk we will summarize the basic
observed properties of these X-ray lags. We will also show some
theoretical results from our numerical modelling of these systems in a
toy model with a lamp-post geometry.
26.05.2014 15:00
Maria Caballero-Garcia
Czech Technical University, Prague
X-ray timing and spectral studies from medium-weight black holes
Abstract
Maria Caballero-Garcia
X-ray timing and spectral studies from medium-weight black holes
A unified characterization of the spectral evolution of black hole binaries has been done in the last 30 yrs. The study of the spectral and aperiodic variability characterizing the X-ray emission from stellar-mass black-hole binaries has revealed to be a very useful tool to understand the mass of the black hole and the physics of accretion on these sources. Ultra-Luminous X-ray sources (ULXs) are accreting black holes that might represent strong evidence of the Intermediate Mass Black Holes (IMBH), proposed to exist by theoretical studies but with no firm detection (as a class) so far. Their X-ray properties have been seen to be different from the case of stellar-mass black hole binaries. I will present the results that we have obtained from two outstanding ULXs (NGC5408 X-1 and the ULXs in M82) and discuss on the properties that can be derived from the study of their X-ray emission.
28.04.2014 15:00
Michal Zajacek
Charles University, Faculty of Mathematics and Physics, Astronomical Institute, Prague
Galactic center Mini-spiral: Interaction modes of neutron stars
Abstract
Michal Zajacek
Galactic center Mini-spiral: Interaction modes of neutron stars
Streams of gas and dust in the inner parsec of the Galactic Center form a distinct feature known as Minispiral, which has been studied in radio and infrared wavebands (Kunneriath et al., 2012). Large fraction of the Minispiral gas is ionized by radiation of stars present in the Nuclear Star Cluster (NSC). Based on the inferred mass in the inner parsec about 10^6 solar masses, over ~10^4 neutron stars should move in the sphere of gravitational influence of the SMBH. We estimate that a fraction of them propagate through denser (ionized) medium concentrated along three arms. Based on the density and the temperature of the gaseous medium, we discuss interaction regimes of magnetised neutron stars passing through the Minispiral region. The simulation results may be applied to other galactic nuclei hosting NSC where the expected distribution of interaction regimes may be quite different.
04.03.2014 14:00
Miroslav Horky
Czech Technical University, Prague
Particle-in-Cell (PIC) simulations of instabilities in weakly ionized plasmas
Abstract
Miroslav Horky
Particle-in-Cell (PIC) simulations of instabilities in weakly ionized plasmas
I will talk about the research done during my stay at the University of Oslo. We simulated plasma instabilities in weakly ionized plasmas under the presence of E x B fields. Both, electrons and ions were magnetised in our simulations and we changed only the type of ion-neutral collisions. For these different ion-neutral collision types we found different electron heating rates and other instability characteristics, such as electrostatic potential fluctuations and electrostatic wave spectra. At first I will present theoretical background of our research, then our results and in the end I would like to introduce current analytical study of the simulated instabilities.
04.02.2014 15:00
Norbert Werner
Kavli Institute for Particle Astrophysics and Cosmology, Stanford University
The Astro-H X-ray observatory
Abstract
Norbert Werner
The Astro-H X-ray observatory
I will talk about the upcoming Astro-H satellite, the next large international X-ray observatory. Astro-H will carry the first high-resolution X-ray imaging spectrometers and will provide an unprecedented wide band coverage that will revolutionize the study of the physics of X-ray plasmas. I will summarize the technical capabilities of the satellite and will present some of the most exciting science goals that we expect to reach with this mission.
27.01.2014 15:00
Frantisek Dinnbier
Astronomical Institute, Academy of Sciences, Prague
Propagating star formation in swept-up shells
Abstract
Frantisek Dinnbier
Propagating star formation in swept-up shells
Shells of swept-up gas are commonly observed at borders of HII regions
and interstellar bubbles. As they expand and accrete new mass, they can
fragment and form new stars. If massive stars are formed, they create
new bubbles and this scenario repeats leading to propagation of star
formation. Despite the importance of shell fragmentation, there is no
consonance in literature how long the unstable wavelengths are and how
fast they grow, especially in the case of higher values of pressure that
confines the shell. In my work I study fragmentation of such shells by
hydrodynamic simulations including a self gravity. A shell which is a
subject to my study is thick and stratified in a direction perpendicular
to its surface. At larger distances, it is truncated by the external
pressure from both sides. I will present first results where I study the
fragment growth rate as a function of the external pressure and compare
my results with analytical estimates made by another authors in the past.
20.01.2014 13:00
Jiri Svoboda
Astronomical Institute, Academy of Sciences, Prague
Study of black holes in active galactic nuclei
Abstract
Jiri Svoboda
Study of black holes in active galactic nuclei
We cordially invite all staff and guests of the Astronomical Institute ASCR to the ceremony of Jan Fric Premium for the year 2013.
The ceremony will take place in the library of the Astronomical Institute ASCR in Ondrejov on Monday, January 20, from 13:00. Since 2009, Astronomical Institute grants the Premium of Jan Fric to young researchers of the Institute for their extraordinary results, which contribute to the international prestige of the Institute. The laureate for 2013 is the employee of the Department of Galaxies and Planetary Systems, Dr. Jiří Svoboda. He received the Premium for the study black holes in active galactic nuclei.
07.01.2014 14:00
Vladimír Karas
Astronomical Institute, Academy of Sciences, Prague
Leftovers from the model of spotted accretion discs
Abstract
Vladimír Karas
Leftovers from the model of spotted accretion discs
A `spotted' accretion disc near a black hole has been studied for a long time as a suitable phenomenological scheme to explain a wide range of variability phenomena. Variety of open issues still persist with this scenario. Based on a recent paper (Wellons et al, http://arxiv.org/abs/1312.3333), we discuss a possibility to further explore effects of strong gravity in the X-ray signal from the inner regions of accreting compact objects.
