Seminars 2013
Michaela Brchnelova
Gymnasium Hubeneho 23, Bratislava
X-ray dynamics measurements of the Tycho’s supernova remnant G120.1+01.4
Abstract
Michaela Brchnelova
Intel International Science and Engineering Fair 2013, international pre-college science competition.
In the following work we present X-ray dynamics measurements of the Tycho’s supernova remnant G120.1+01.4. We compare observations and spectra from 2005 and 2009 archived in XMM-Newton Science Archive in order to determine differences caused by collision with surrounding interstellar medium (ISM) as well as by remnant’s own expansion. We have calculated the azimuthal expansion of remnant’s edges to vary from 0.194 arcsec/yr to 0.438 arcsec/yr, while the highest values are found to have the azimuth of about 60° in the south-east and the lowest expansion overall is estimated on the north. Comparison of fluxes has shown that the highest estimated energy gain of 3.1 times was measured in reverse shock region around the azimuth of 300° in the energy range from 6.1 keV to 8 keV, whereas the highest energy loss was found to be in the same energy range in forward shock region with the azimuth of approximately 70° reaching 2.4 times lower energy compared with the values from 2005. We have also defined the most abundant heavy elements within energy scale from 200 eV to 8 keV, which are identified through spectral lines to be Fe XVIII (0.849 keV), Mg XI and XII (1.34 keV, 1.46 keV), Si XIII (1.83 keV), S XV (2.41 keV, 2.86 keV) and Ca XIX (3.84 keV).
Grischa Karssen
I. Institute of Physics, University of Cologne, Germany
Orbiting plasma cloud in strong gravity
Abstract
Grischa Karssen
Presentation of an ongoing PhD project. In this talk I will present some of the results of simulations of a plasma blob, assumed to be a synchrotron source, in Keplerian orbit around a black hole. This is a model which could explain the flares of SgrA* in the NIR.
Steven N. Shore
Università di Pisa
V407 Cygni 2010 - The answer is blowin' in the wind
Abstract
Steven N. Shore
The otherwise garden variety, almost boring symbiotic stay V407 Cygni turned into one of the most important novae of the last century without warning in Mar. 2010. It made astronomical history by being the first nova detected by the Fermi/LAT in high energy gamma-rays and was observed for more than a year in a multi-site panchromatic campaign in which Ondrejov played an important role. This nova explosion occurred in a wind-dominated binary system and the details of the event illuminate a wide range of previously unrelated and poorly understood astrophysical processes. This talk will highlight some of the physical insights gained from the study of this extraordinary event.
Michal Bílek
Astronomical Institute, Academy of Sciences, Prague
Shell galaxy NGC 3923 and the missing mass problem
Abstract
Michal Bílek
The missing mass problem is one of the main questions of modern physics.
The two main candidates to its solution are the dark matter and the
modified Newtonian dynamics (MOND). I will give a short introduction into
MOND. Some elliptical galaxies are surrounded by faint arc-like features
called the shells. The shells are remnants of minor galaxy mergers. I will
describe the mechanism of the shell formation and say, how the shell
distribution is connected with the host galaxy's potential. Using the
laws of shell evolution, I tried to discern, whether the shells system
surrounding NGC 3923 can be better reproduced in MOND or in classical
dynamics with NFW dark haloes (resulting from LambdaCDM simulations)
employing a new method. The currently available data do not allow to make
a clear decision, because we were able to model the shell distribution
equally well in the both theories. However, we made a prediction where yet
unknown shells should be located. The prediction of MOND and LambdaCDM are
different for them. Furthermore, the method employed also allowed to
reveal the details of formation of the shell system surrounding NGC 3923
and, if LambdaCDM is correct, gave constraints on its dark halo.
Steven M. Kahn
Stanford University
The Large Synoptic Survey Telescope
Abstract
Steven M. Kahn
The Large Synoptic Survey Telescope (LSST) will be a large-aperture, wide-field, ground-based telescope designed to provide deep images of half of the total sky in six optical colors every few nights. As such it will enable a wide variety of diverse astronomical investigations, ranging from making a census of small moving objects in the solar system, to mapping the outer regions of our Milky Way galaxy. Of particular interest for cosmology and fundamental physics, LSST will provide tight constraints on the nature of dark energy through a range of statistical analyses of the shapes and distributions of billions of galaxies out to moderate to high redshift. This project was recently ranked as the highest priority new ground-based astronomical facility by a committee of the US National Academy of Sciences. I will review the basic considerations that have led to the design of the LSST, and discuss a sampling of the exciting science opportunities that will be enabled by its construction.
Bartosz Dabrowski
Astronomical Institute, Academy of Sciences, Ondrejov
News from ALMA
Abstract
Bartosz Dabrowski
The Atacama Large Millimeter/submillimeter Array (ALMA) is a major new facility for world astronomy. When completed in 2013, ALMA will consist of a giant array of 12-m antennas, with baselines up to 16 km, and an additional compact array of 7-m and 12-m antennas to greatly enhance ALMA's ability to image extended targets. Construction of ALMA started in 2003. The ALMA project is an international collaboration between Europe, East Asia and North America in cooperation with the Republic of Chile.
ALMA Early Science Cycle 1 observations will start in January 2013 and span 10 months. It is anticipated that approximately 800 hours of array time will be available for Cycle 1 projects.
I will present the Czech ALMA Node activity during the previous year.
Ondrej Pejcha
Ohio State University
The explosion mechanism of core-collapse supernovae and its observational signatures
Abstract
Ondrej Pejcha
Abstract: Many massive stars explode as core-collapse supernovae. Supernova simulations show that the shock wave accompanying formation of the proto-neutron star evolves into a quasi-static accretion shock and it proves difficult to revive its outward propagation. The stalled accretion shock turns into explosion when the neutrino luminosity from the collapsed core exceeds a critical value L_crit (the "neutrino mechanism"). I will show the connection between the steady-state isothermal accretion flows with bounding shocks and the neutrino mechanism: there is a maximum, critical sound speed above which it is impossible to maintain accretion with a standoff shock. I will derive the "antesonic" condition, which characterizes the transition to explosion over a broad range in accretion rate, PNS properties and microphysics. Additionally, I will characterize the effects of accretion luminosity and collective neutrino oscillations on L_crit. The physics of the explosion mechanism and the progenitor structure are imprinted in the observed distribution of neutron star masses. I will use Bayesian analysis to model the double neutron star mass distribution to infer the properties of the progenitor binary population, fallback during the explosion, and constrain the mass coordinate where the explosion develops.
The Physics of the Neutrino Mechanism of Core-collapse Supernovae
http://adsabs.harvard.edu/abs/2012ApJ...746..106P
Effect of collective neutrino oscillations on the neutrino mechanism
of core-collapse supernovae
http://adsabs.harvard.edu/abs/2012MNRAS.425.1083P
The observed neutron star mass distribution as a probe of the
supernova explosion mechanism
http://adsabs.harvard.edu/abs/2012MNRAS.424.1570P
The progenitor dependence of the neutrino mechanism of core-collapse supernovae
Pejcha & Thompson, in preparation