Seminars
Our seminars take place in the lecture room of the building at Praha–Sporilov.
Next seminar:
Luigi Stella
INAF - Osservatorio Astronomico di Roma
The Large Observatory for X-ray Timing (LOFT)
Abstract
Luigi Stella
High-time-resolution X-ray observations of compact objects provide direct access to strong-field gravity, to the equation of state of ultradense matter and to black hole masses and spins. A 10 m2-class instrument in combination with good spectral resolution is required to exploit the relevant diagnostics and answer two of the fundamental questions of the European Space Agency (ESA) Cosmic Vision Theme "Matter under extreme conditions", namely: does matter orbiting close to the event horizon follow the predictions of general relativity? What is the equation of state of matter in neutron stars? The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the four Cosmic Vision M3 candidate missions to undergo an assessment phase, will revolutionise the study of collapsed objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei. Thanks to an innovative design and the development of large-area monolithic silicon drift detectors, the Large Area Detector (LAD) on board LOFT will achieve an effective area of ~12 m2 (more than an order of magnitude larger than any spaceborne predecessor) in the 2-30 keV range (up to 50 keV in expanded mode), yet still fits a conventional platform and small/medium-class launcher. With this large area and a spectral resolution of <260 eV, LOFT will yield unprecedented information on strongly curved spacetimes and matter under extreme conditions of pressure and magnetic field strength.
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
Previous seminar:
Lydia Moser
I. Institute of Physics, University of Cologne, Germany
Galactic centers near and far: First interferometric observations of 3 galaxies of the Borderline Type 1 QSO Sample and of the Galactic Center (Sgr A*) with the SMA and ALMA
Abstract
Lydia Moser
In my talk I will give a short insight into my recent work which can be divided into two research topics related to black holes, i.e. active galactic nuclei (AGN) and the Galactic Center.
The strong correlation between the black hole mass and the central velocity dispersion of galaxies suggests a coeval growth of supermassive black holes (SMBH) and the surrounding stellar bulges. The growth is believed to be regulated by an interplay of a nuclear fueling, i.e. inflow of gas which is then consumed by star formation and accretion onto the SMBH, and a feedback from these regions such as winds, outflows and radiation. The diverse mechanisms that might be involved in these processes (e.g. galactic interactions or secular processes) are topics of current research. Going down to smaller scales little is known about the interaction of the SMBH with its immediate environment. Our own Galactic Center offers us a unique laboratory to study the physics around the SMBH, Sagittarius A*, on sub-parsec scales.
In the first part of my talk I present interferometric observations of three barred galaxies from our Borderline Type 1 QSO (B1Q) sample with the Submillimeter Array (SMA) in the CO(2-1) and (3-2) line transition. The goal of the sample is to investigate the nuclear fueling in type-1 active galactic nuclei (AGN) with magnitudes around the classical Seyfert/Quasi-Stellar Object (QSO) demarcation, all located in the volume 0.01 < z < 0.06. We intend to study the evolutionary link between the local population and the more active galaxies at higher redshifts. As preliminary result we find that all three galaxies are rich in molecular gas with masses ranging from 1.3—11 x 10^9 M_sun, and two of them can be classified as luminous infrared galaxies (LIRGs) indicating high star formation activity. The region of CO emission is very compact, i.e. FWHM < 1.7 kpc, and only in one case the molecular gas also extends along the galactic bar. From the two galaxies with a compact CO emission region, one shows signatures of an inflow. The continuum flux is not detected which is consistent with an expected dust contribution of less than 50 muJy.
The second part is about radio continuum and line emission maps at 230 GHz and 345 GHz obtained from a single night's observation of the Galactic Center with the SMA and - for the first time - with the Atacama Large Millimeter Array (ALMA) at 230 GHz. While the ALMA mosaic covers only the mini-spiral region, the SMA data includes also most parts of Sagittarius A West and the surrounding circumnuclear disk. Sgr A West is partially detected in continuum emission and the H30alpha (~231 GHz) recombination line emission map outlines well the distribution of the ionized gas as well as its radial motion. I present the first high resolution (5") map of the Galactic Center region in CO(3-2) emission - it traces the molecular gas in the circumnuclear disk. For future analyses of the variability of Sgr A*, I extracted the lightcurves of the Sgr A*. They show a significant difference in the average flux level between the two observations with ALMA and SMA, that are separated by only 2.5 hours.
If you would like to give a seminar in our group, please contact Vladimir Karas or Jaroslav Hamersky.