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Weekly Seminars for October 2013 Print E-mail
Monday October 7, 2013 4,00 pm
Aula Conversi (Physics Dept., Old Building - 1st Floor)
 
  Seminar of Astrophysics
 
Speaker: Dr. Veronica BIFFI

Institution: International School for Advanced Studies - SISSA, Trieste

Title: On the scaling relations of X-ray galaxy clusters.  

Abstract:  
The physics of galaxy clusters finds a precious source of information in X-ray observations, which provide us with an increasingly complex and detailed picture of these structures. Theoretically, up-to-date hydrodynamical simulations can currently address many questions about the cluster dynamics and physics, and it becomes more and more vital to find a direct and faithful way to compare their results to real X-ray data. To this purpose, we apply the X-ray virtual telescope PHOX and generate mock X-ray observations out of hydrodynamical simulations. In this way, we can address a number of interesting issues, such as the reconstruction of the cluster temperature distribution via spectral analysis or the investigation of scaling relations among global observable properties. I will present results on a large sample of simulated clusters, dedicated to investigate their self-similar appearance in the X-ray band and via the Sunyaev-Zel'dovich signal, and the agreement with real cluster data. 
 
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La Segreteria ICRA
c/o Dipartimento di Fisica
Sapienza Università di Roma
P.le A. Moro, 5
I - 00185 ROMA, Italy
tel.: +39 06 4991 4 254
fax: +39 06 4454992
email:
segreteria@icra.it
 
 
Thursday October 24, 2013 4,00 pm
Aula Conversi (Physics Dept., Old Building - 1st Floor)
 
  Seminar of Astrophysics
 
Speaker: Dr. Francesco SYLOS LABINI

Institution: Centro Studi e Ricerche Enrico Fermi; Istituto dei Sistemi Complessi CNR

Title: Violent and mild relaxation of an isolated self-gravitating uniform and spherical cloud of particle.  

Abstract:  
The gravitational relaxation process acting during the collapse of a self-gravitating and isolated cloud of particles is the fundamental physical mechanism underlying the formation of virialized structures both in astrophysical and cosmological contexts. These structures, although never reach thermodynamical equilibrium, represent long-lived states whose lifetime diverge with the number of system particles. . The understanding of the relaxation process should eventually explain the density profiles observed in the simulations of both isolated and non isolated self-gravitating! systems and of the luminosity profiles of globular clusters and elliptical galaxies. We firstly discuss the dynamics of an isolated cloud of particles and then we consider the cosmological case. In this latter case the evolution such a structure represents a useful toy model to test the accuracy of a cosmological N-body code in the non linear regime. We show that the density profile of the virialized structure can be strongly affected by numerical artifacts and that the Navarro Frenk White density profile can be originated by numerical problems. 
 
**************************************************
La Segreteria ICRA
c/o Dipartimento di Fisica
Sapienza Università di Roma
P.le A. Moro, 5
I - 00185 ROMA, Italy
tel.: +39 06 4991 4 254
fax: +39 06 4454992
email:
segreteria@icra.it
 
 
Thursday October 31, 2013 - 3,00 pm
Sala Direzione INFN (Physics Dept., Old Building - 2nd Floor)
 
  ICRA Seminar
 
Speaker: Prof. Lev TITARCHUK

Institution: University of Ferrara and GSFC (Goddard Space Flight Center - USA)

Title: Black hole signature and QPO phenomenon.  

Abstract:  
I present a study of correlations between X-ray spectral and timing properties observed from a number of Galactic black hole (BH) binaries during hardsoft state spectral evolution. 17 transition episodes from eight BH sources observed with Rossi X-Ray Timing Explorer were analyzed. Our scaling technique for BH mass determination uses a correlation between the spectral index and quasi-periodic oscillation (QPO) frequency. In addition, we use a correlation between the index and the normalization of the disk seed component to cross-check the BH mass determination and estimate the distance to the source. While the indexQPO correlations for two given sources contain information on the ratio of the BH masses in those sources, the indexnormalization correlations depend on the ratio of the BH masses and the distance square ratio. In fact, the indexnormalization correlation also discloses ! the indexmass accretion rate saturation effect given that the normalization of disk seed photon supply is proportional to the disk mass accretion rate. I present arguments that this observationally established index saturation effect is a signature of the bulk motion (converging) flow onto a BH, which was early predicted by the dynamical Comptonization theory. I use GRO J1655−40 as a primary reference source for which the BH mass, distance, and inclination angle are evaluated by dynamical measurements with unprecedented precision among other Galactic BH sources. I apply our scaling technique to determine BH masses and distances for Cygnus X-1, GX 339−4, 4U 1543−47, XTE J1550−564, XTE J1650−500, H 1743−322, and XTE J1859−226. A good agreement of our results for sources with known values of BH masses and distance provides independent verification for our scaling technique. 
 
**************************************************
La Segreteria ICRA
c/o Dipartimento di Fisica
Sapienza Università di Roma
P.le A. Moro, 5
I - 00185 ROMA, Italy
tel.: +39 06 4991 4 254
fax: +39 06 4454992
email:
segreteria@icra.it
 
 
Thursday October 31, 2013 - 4,00 pm
Aula Conversi (Physics Dept., Old Building - 1st Floor)
 
  Seminar of Astrophysics
 
Speaker: Prof. Yoel REPHAELI

Institution: School of Physics and Astronomy, Tel Aviv University, Israel and Center for Astrophysics and Space Sciences, University of California, San Diego, USA

Title: Cluster & Filament SZ Anisotropy and Cosmological Parameter Bias.  

Abstract:  
I will review our recent work on modeling cluster SZ number counts and power spectra, and the additional power due to scattering of the CMB by gas in filaments. Precise cosmological parameter extraction from CMB primary anisotropy necessitates reasonably accurate accounting for the combined anisotropy induced by clusters and filaments. I will disucss the levels of parameter bias due to the unavoidable residual signal from these structures. 
 
**************************************************
La Segreteria ICRA
c/o Dipartimento di Fisica
Sapienza Università di Roma
P.le A. Moro, 5
I - 00185 ROMA, Italy
tel.: +39 06 4991 4 254
fax: +39 06 4454992
email:
segreteria@icra.it
 
 
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