Studying Gamma Ray Bursts from a new perspective

Dr. Giancarlo Ghirlanda

INAF – Brera Astronomical Observatory, Italy

v ponedeljek, 3. junija 2013, ob 13h v F4

I will summarize the current observational status of the prompt emission of Gamma Ray Bursts and discuss some related issues: thermal vs non-thermal components, the nature of the high energy [GeV] component and the “color”-luminosity correlations.

A step forward in understanding the physics of Gamma Ray Bursts is to consider their comoving frame properties. I will show that accounting for the relativistic beaming, GRBs appear to have a nearly “universal” comoving-frame energy/luminosity. This offers a unifying interpretation of the “color”-luminosity relations if there is a link between the geometry and the dynamics in GRB outflows.

Through the results of a population synthesis code the expected dynamical and geometrical properties of GRBs as a population are derived and predictions for the detection rate of GRBs at long wavelengths by forthcoming radio facilities will be presented.

Active Galactic Nuclei in the Fermi and Cherenkov Era

Prof. Massimo Persic

INAF – Astronomical Observatory of Trieste, Italy

v ponedeljek, 13. maja 2013, od 10h do 13h v F6

Predavanje bo izvedeno v sklopu predmeta Astrofizika zvezd in Galaksije za študente na 2. bolonjski stopnji.

A review of the fundamental properties of AGN (sources of energy, relativistic jets, beaming, radiative processes) will lead us to critically evaluate recent and ongoing advancements afforded by the current generation of orbiting and ground-based gamma-ray telescopes. Special attention will be devoted to studying those AGN whose central engine shows up at its most naked – blazars.

Probing the Dark Universe with the Cosmic Growth

Prof. Stefano Borgani

Department of Physics, University of Trieste and INAF – Astronomical Observatory of Trieste, Italy

POZOR, Astrodebata ODPADE

I will discuss the role that cosmological tests based on measurements of the growth rate of density perturbations have in constraining the nature of dark matter and dark energy, as well as the nature of gravity. After reviewing the basic concepts on the evolution of density perturbations, I will highlight how such predictions are altered by modifying gravity. Furthermore I will discuss how neutrino masses can be inferred from cosmological observations, through the effect that massive neutrinos have on the growth rate of perturbations. Galaxy clustering, weak lensing and clusters of galaxies will be discussed as tracers of growth of density perturbations.

Finally I will discuss the role that future large galaxy surveys, like that to be provided by the Euclid satellite, will have in shedding light on the dark sector of the Universe.

The Golden era of GeV astrophysics

dr. Francesco Longo

Department of Physics, University of Trieste and INFN Trieste

ponedeljek, 25. 3. 2013 ob 13h v F4

The contemporaneous observations of the high energy sky (>100 MeV) provided by the AGILE and the Fermi satellites, launched in 2007 and 2008 respectively, are providing the unique opportunity to study the variable gamma ray sky with unprecedented coverage and sensitivity.

In this seminar the main results in the Galactic and the Extragalactic sky by these two missions will be presented and discussed.

Past, present and future of the Intergalactic Medium Cosmology (a European perspective)

prof. dr. Stefano Cristiani

INAF – OATS, Italy

torek, 19. 3. 2013 ob 13h v F3

The history of the universe during and soon after the Dark Age is recorded in the all-pervading intergalactic medium (IGM), which is believed to contain most of the ordinary baryonic material resulting out of the big bang. Throughout the epoch of structure formation, the IGM became clumpy and acquired peculiar motions under the influence of gravity and acted as a reservoir for the gas that gets accreted, cools and forms stars within galaxies and as a sink for the metal-enriched material, energy and radiation which they eject.

Along the line of sight to a distant source – a quasar, a gamma-ray burst, a galaxy – every parcel of IGM gas selectively absorbs certain wavelengths of light due to the presence of the various chemical elements in it. Through the analysis of these absorption lines we can study the spatial distributions, motions, chemical enrichment, and ionization histories of gaseous structures from redshift seven and beyond until the present. From few details of little apparent significance, it is possible to deduce a surprising number of important conclusions about our Universe, especially when we link the information provided by absorption lines with the complementary information derived from the evolutionary properties of luminous galactic structures. The study of the IGM has enormously developed in the last 50 years, and so the contribution of Europe to it, overcoming the initial handicap of collecting power, detectors and tradition.

Prehodni pojavi v Sončevem vetru

dr. Primož Kajdič

Institut de Recherche en Astrophysique et Planétologie (Toulouse, Francija)

ponedeljek, 26. 2. 2013 ob 14h v F5

Tekom predavanja bom opisal pojave, ki so posledica interakcije Sončevega vetra z udarnimi valovi v njem. V grobem lahko udarne valove v Osončju razdelimo na dve skupini: v prvi so planetarni udarni valovi, ki nastanejo zaradi interakcije med Sončevim vetrom ter planeti oziroma njihovimi magnetosferami, v drugi skupini pa so medplanetarni (MP) udarni valovi. Slednji so bodisi posledica hitrih struktur v MP prostoru, kot so medplanetarni izbruhi koronalne mase, bodisi nastanejo z interakcijo med hitrim ter počasnim Sončevim vetrom.

Za vse omenjene udarne valove je značilna odsotnost binarnih trkov med delci (ioni, elektroni), zato pomemben mehanizem za disipacijo kinetične energije sončeve plazme ob prehodu skozi tak udarni predstavljajo interakcije med delci ter magnetnimi polji. Ko je magnetosonično Mahovo število udarnega vala večje od neke mejne vrednosti, je eden od načinov disipacije ta, da udarni val del delcev v prihajajoči plazmi reflektira nazaj v območje pred njim. Če so izpolnjeni določeni pogoji, lahko interakcija teh povratnih delcev z delci v prihajajočem Sončevem vetru močno perturbira območje pred udarnim valom, kar nato privede do cele palete raznih prehodnih struktur v tem območju.

V zadnjih desetletjih smo z raznimi misijami, kot so npr. Stereo, ACE, Wind, Cluster in Themis, dobili jasnejši vpogled v dogajanje v območjih pred udarnimi valovi, kar nam je omogočilo primerjavo teoretičnih izračunov s podatki in-situ.

Cosmic signatures of the early Universe

dr. Umberto Maio

INAF – OATS, Italy

ponedeljek, 18. 2. 2013 ob 13h v F4

Results from high-resolution N-body, hydro, chemistry simulations, including molecule creation, star formation, stellar evolution, metal spreading, and feedback effects will be presented.

Early structure formation and the transition from the primordial population III to the standard population II-I star formation regime will be discussed, with particular emphasis on the implications for high-redshift metal pollution, luminosity functions, (long) gamma-ray burst rate from different stellar populations, and the properties of the corresponding hosting galaxies.

The resulting scenarios in alternative (non-Gaussian) cosmologies will be addressed, as well.

GRB Jet Breaks and Energetics in the Swift/Chandra era

Ponedeljkov fizikalni kolokvij

IZJEMOMA v petek 21. decembra 2012, ob 11:15 v predavalnici F1

Prof. David N. Burrows, Department of Astronomy and Astrophysics, Penn State University, State College, PA, USA

Gamma-Ray Bursts emit tremendous amounts of energy on timescales ranging from less than a second to hundreds of seconds. We have strong evidence that they must be highly beamed, which means that our knowledge of their true energetics relies on understanding the beaming angles of the relativistic jets. The jet opening angles can in principle be measured through the characteristic “jet break” in the GRB light curves. Work a decade ago suggested that these jet breaks occur on typical timescales of a few days. The Swift satellite, which produces detailed, relatively uniform light curves for GRBs that often extend to a few weeks after the explosion, was expected to measure jet breaks on a regular basis, providing good determinations of jet opening angles. To our surprise, this has not been the case. Swift has found much more complex light curves than anticipated on the basis of earlier data, but cases of clear jet breaks are present in only a few percent of the more than 730 GRBs observed to date by Swift. Theoretical work over the past several years has suggested various explanations for the lack of clear jet break signatures in the Swift X-ray light curves.

Recent GRB jet models are now providing a good framework for fitting light curves to detailed hydro/radiation codes that may allow us to finally begin measuring the jet properties for a large class of GRBs. We have begun to apply these models to data sets that feature good X-ray light curves from Swift XRT and Chandra ACIS observations, and I will discuss preliminary results from that work.

Galactic Archaeology in Light of Migrant Stars

Dr. Rok Roškar

Institute for Theoretical Physics, University of Zürich

petek, 21. 12. 2012, ob 10h v F3

The disks of spiral galaxies build up through a variety of processes. The demographics of stars, their kinematic and chemical properties, that we observe today represent a historic record of these past events.

Recently, it has been recognized that stars can efficiently “surf” on the crests of spiral waves throughout the disk, meaning that their present-day locations may have nothing to do with their birth environment. This radial mixing makes the disk a much more diverse place and galactic archaeology much more difficult.

I will discuss the recent advances in our understanding of this process, its implications ranging from astrobiology to extragalactic disks, and place it in the context of cosmological galaxy formation.

Our Universe at Intergalactic Scales

dr. Matteo Viel


torek, 30. 10. 2012, ob 14h v F6

I will discuss the cosmological importance of the matter that is filling the space between galaxies: the Intergalactic Medium (IGM). I will focus on three IGM-related issues: its role as a tracer of the large scale structure; how it can be used to constrain fundamental physical properties (nature of dark matter, variation of fundamental constants and more importantly neutrino masses); its relationship with the galaxy formation process.
The results are based on high and low resolution Lyman-alpha forest quasar spectra (BOSS/SDSS-III and VLT/UVES) and state-of-the-art hydrodynamic simulations.