Talks Second Bego (Nice) Print E-mail





  • Felix Aharonian (Dublin Institute for Advanced Studies, Dublin, Ireland; Max-Planck-Institut for Kernphysis, Heidelberg, Germany)

Why very high energy gamma-rays?

I will discuss main objectives and motivations of gamma-ray astronomy, its uniqueness and its to other branches of modern astrophysics. The lecture ill consist of three parts: 1. Introduction - general remarks; 2. Cosmic gamma ray source populations; 3. Gamma-ray production mechanisms in astrophysical environments.

  • Lorenzo Amati (INAF - Istituto di Astrofisica Spaziale e Fisica cosmica, Bologna, Italy)

GRB science with LOFT

LOFT is a satellite mission currently in Assessment Phase for the ESA M3 selection. The payload is composed of the Large Area Detector (LAD), with 2-50 keV energy band, a peak effective area of about 10 m2 and an energy resolution better than 260 eV, and the Wide Field Monitor (WFM), a coded mask imager with a FOV of several steradians, an energy resolution of about 300 eV and a point source location accuracy of 1 arcmin in the 2-30 keV energy range. Based on preliminary considerations and estimates, we show how the scientific performances of the WFM are particularly suited to investigate some of the most relevant open issues in the study of GRBs: the physics of the prompt emission, the spectral absorption features by circum-burst material (and hence the nature of the progenitors), the population and properties of XRFs, and the detection and rate of high.z GRBs. Measurements of the early afterglow emission with the Large Area Detector (LAD) may also be possible depending on the mission slewing capabilities and TOO observations policy.

  • Bruno Sversut Arsioli (Universidade Estadual de Campinas (UNICAMP), Instituto de Física Gleb Wataghin (IFGW), Brazil)

Active Galactic Nuclei: Blazars
The main characteristics of Blazars and a study of the new WISE-HSP sample.

Blazars are a class of active galactic nuclei (AGN) characterized by rapid and large amplitude spectral variability, mainly due to the presence of a relativistic jet pointing very close to the line of sight. The spectral emission of those objects contain strong non-thermal radiation content along the whole energy band, from radio to hard gamma-rays. Usually the observed radiation shows extreme properties, mostly coming from relativistic amplification effects. Their spectral energy distribution (SED) present a general shape composed of two bumps, one in the IR to soft x-ray band and the other in the hard x-ray to gamma-rays. According to the standard picture, the first peak is associated with the emission of synchrotron radiation due to a relativistic electrons moving in a feeble magnetic field and the second peak is associated with photons which are Inverse-Compton (IC) scattered to higher energies by the same electron population (seed photon ongoing IC can originate from the accretion disk and the broad line region). In this context a blazar is classified as High Synchrotron peaked (HSP) if the synchrotron peak frequency > 10^15 Hz. Therefore, by definition HSP objects are very bright sources of X-rays and compose a significant part of the Cosmic X-ray Background (CXB), (Giommi, 2008). Observations have shown that HSPs are bright sources of high energy TeV photons (nu > 10^25 Hz). They would be the dominant component of the TeV background, a concept that is still not well established. According to low density distribution of such objects in the sky, the TeV background would be composed by spread and discrete sources, in contrast with the diffuse background light that is observed for lower energies. Many questions are still under debate in what concerns the absorption features at TeV energies. Therefore, it is a straight task to build a complete catalog of HSP objects in order to provide important targets for gamma-ray and TeV detection, allowing a better description of the blazars SEDs. Clearly, within the motivations for identifying extremes AGNs are the possibility of studding jet properties in extreme condition, and determining population distribution of HSPs. Moreover, since they can be detected in a broad range of redshifts, extreme blazars together with cluster of galaxies may be an efficient tool for studding cosmological evolution (Puccetti, 2006). The SEDs of HSP objects are extremely peculiar and no other type of extra-galactic sources are known to posses such features. Imposing selection rules (like color-color selection and multi-wavelength flux ratio limits) consistent with the HSP SEDs, allow us to identify them within large amount of objects coming from all-sky surveys (like WISE: Infrared all sky survey), and so to build up representative samples with high selection efficiency.
The new WISE HSP will be presented. It contains about 450 objects, and its main characteristics will be discussed.

  • Diego Cáceres (Universidad Nacional de Colombia)

Equillibrium equations of magnetized white dwarfs


  • Alessandro De Angelis (INFN-­U.Udine/INAF/LIP-­IST, Lisboa)

VHE cosmic γ rays and fundamental physics (with emphasis on photon propagation)

Introduction: why gamma rays? How?
Some results related to fundamental physics
What’s next

  • Massimo Della Valle (Astronomical Observatory of Capodimonte, Naples, Italy)

Gamma-ray Bursts as Cosmological Rules


  • Filippo Frontera (University of Ferrara)

Comptonization signatures in GRBs

Using a sample of 4 bright GRBs simultaneously detected with both the BATSE experiment and the WFCs aboard BeppoSAX, it was possible to perform a time resolved spectral analysis from 2 to 2000 keV, a band still scarcely explored in the low energy part. In this peculiar energy band, we tested the Epi-Liso correlation and some photospheric models: the model proposed by Ryde and Pe'er (2009), the model proposed by different authors (e.g., Guiriec et al. 2011) to describe some time-resolved spectra of GRB detected with Fermi, in which a black body is added to the Band function (e.g. Guiriec et al. 2011), and, last but not least, the Comptonization model proposed by Titarchuk et al. (2012). I will present some relevant results of our results.

  • Kleinert Hagen (Free University of Berlin)

Conformal Gravity with Fluctuation-Induced Einstein Behavior at Long Distances

Conformal Gravity is renormalizable and has strong fluctuations capable of generating spontanaously an Einstein term in the action, as a kind of “dimensionlly transmuted coupling constant”. We show that this may produce the correct long-range behavior of gravitational forces.

  • Daniele Gregoris (Stockholm University)

The Stokes' law in general relativity: formulation and applications

Friction forces play an important role in many natural phenomena. Although widely understood in classical mechanics, they have recently received new interest in the context of general relativity. In this talk I will show how to write the Stokes formula using a general relativistic formalism reobtaining the Poyting-Robertson expression and I will present some applications in astrophysics and cosmology of this result. The motion of a body inside a photon gas or a massive fluid is discussed inside the metric of Schwarzschild, Tolman and Pant-Sah and Friedmann-Robertson-Walker respectively. In this last case I will discuss the role of dissipative effects in the evaluation of peculiar velocities.

  • Shabnam Iyyani (Stockholm University)

Fermi observations of the jet photosphere in GRBs: GRB110721A

Fermi Gamma Ray Space Telescope observations of the prompt emission in gamma-ray bursts (GRBs) have provided evidence that several different spectral features can be present in burst spectra. One such feature is the emission from the jet photosphere, which has been shown to play a significant role in the formation of the spectrum in several strong bursts. In this talk, I will present characteristic Fermi bursts which illustrate the various appearances that the photosphere can have in GRBs. In particular, based on these observations, I will show how the dynamics of the jet can be estimated and what we can learn about the physical processes involved. I will also discuss geometrical and physical processes that will broaden the photosphere spectrum that is expected from a relativistic outflow and show how this can explain the observations. Finally, I will compare these Fermi results with the results found for the photospheric emission detected in CGRO BATSE observations.

  • Christoph H. Keitel (Max Planck Institute for Nuclear Physics (MPIK))

Extremely high-intensity laser interactions with fundamental quantum systems

Laser-vacuum interaction: Vacuum refractivity, matterless double slit, pair creation
Laser-electron interaction:GeV laser colliders, pair creation, radiative reaction, cascades
Laser-ion & nuclei interaction: ion acceleration for cancer treatment, nuclear population transfer, laborat. astrophysics

pdf Presentation 

  • Hendrik Ludwig (University "La Sapienza ROMA")

Extraction of gravitational energy through strong electric fields

I will discuss models that are suitable to investigate the buildup of strong electric fields in compact objects at equilibrium, oscillation and collapse. These electric fields can provide a very effective and elegant method of extracting gravitational energy via vacuum polarization.

  • Nazzareno Mandolesi (INAF IASF BOLOGNA)

CMB Cosmology

I will review the most recent results on CMB Cosmology, including Planck 2013, and give an outlook to future space missions in the field. Possible anomalies in the Planck results will be briefly discussed.

  • N. E. Mavromatos (King's College London and CERN-PH-TH)

Neutrinos and the Universe

I discuss various aspects of neutrino physics in extensions of the Standard Model involving sterile (right-handed) neutrino states and their role in Astrophysics, Cosmology and in general the Physics of the Early Universe. In particular I will discuss aspects of oscillations, mass generation, and interactions among sterile neutrinos and the standard model sector with a view to study their role on Leptogenesis, Baryogenesis, Dark Matter and Large scale structure of ther Universe. Concerning Dark Matter, I will revisit the current constraints, including Planck Data, with a view to support ideas that sterile neutrinos with masses of order of a few keV can play the role of viable dark matter candidates, consistent with current data.

  • Volker Perlick (ZARM, U. Bremen, Germany)

Gravitational Lensing beyond the weak-field approximation

Until a few years ago, the theory of gravitational lensing was usually done in an approximation formalism, based on the assumptions that the gravitational field is weak and that bending angles are small. In principle, however, bending angles can be arbitrarily large, i.e., light rays can make arbitrarily many turns around compact massive objects. In this talk I discuss a general formalism, based on an exact lens equation, for describing gravitational lensing situations with arbitrarily large bending angles. The general formalism is then applied to Sagittarius A*, the object at the centre of our galaxy. In particular, it is discussed how a black hole can be distinguished from other compact objects by observing its 'shadow'. The observation of the shadow of Sagittarius A* should be within the reach of the Event Horizon Telescope and other upcoming instruments.

  • Mirzoyan Razmik (Max-Planck-Institute for Physics Munich, Germany)

Light in Our Life and in Science: How Do We Measure It

Light is playing a major role in our life, ~80% of information we obtain through our visual perception. Also in physics measurement of light is playing a central role. We are measuring Cherenkov light from gases (accelerator Cherenkov experiments), atmosphere (air Cherenkov and air fluorescence experiments), in water (neutrino experiments), from scintillation counters. Also in medical diagnostics detection of light is playing a central role. Unlike human eyes the physicists developed sensors for measuring light that are inferior in some senses like, for example, the dynamic range, but they are superior in many other senses like, for example, the sensitivity and the speed. The sensitivity of some special light sensors exceed that of human (and other living creature) eyes by an order of magnitude, these can easily capture ultra-fast light flashes and images and even display their development in time. Emission of light is accompanying an enormous variety of processes, starting form stars and ending with human bodies. Even the light sensors that are supposed only to detect light, are emitting their own weak light. In my presentation I am going to dwell on the importance and ways of measuring light, putting special accent on the state-of-the-art light sensors.

  • Lev Titarchuk (University of Ferrara; ICRANET; Goddard Space Flight Center)

X-ray spectral index correlations vs mass accretion rate in neutron star and black hole X-ray binaries in their different spectral states. Theory vs observations

We present details of observations of neutron star (NS) and black hole (BH) binaries and the first principle theory of X-ray spectral formation in neutron star (NS) and black hole (BH) binaries. We show our model predicts the spectral index correlation vs mass accretion rate as in the case of NS as well in the BH case. In BHs the spectral index should increase and then saturate with mass accretion rate because the index as an inverse of Comptonization parameter Y and Y-parameter saturates with the high mass accretion in the converging flow onto BH. Comparison of this model prediction with X-ray observations shows that in BH case the index, indeed, correlates and then saturates with mass accretion rate. Moreover this index-mass accretion rate correlation allows us to estimate BH masses and distance to the source. While in NS sources the observations shows that the index stays the same independently of spectral state of the source which can be possible if the energy release in the disk is always much smaller of that at NS TL (boundary layer).

  • She Sheng Xue (ICRANet)

Vacuum pair-production in a classical electric field and an electromagnetic wave

Using semi-classical WKB-methods to treat the production of electron and positron pairs by a strong electric field from the vacuum as a quantum tunneling process we show derivation of a general expression for the pair production rate in a z-dependent electric field E pointing in the z direction. We also allow for a smoothly varying magnetic field B parallel to E. The boundary effects of the confined fields on pair-production rates are exhibited. A simple variable change in all formulas leads to results for electric fields depending on time rather than space. In addition, we discuss tunnelling processes in which empty atomic bound states are spontaneously filled by negative-energy electrons from the vacuum under positron emission. Furthermore, we show the calculation of the rate of electron-positron pair-production from the vacuum in the presence of two external fields, a strong (space- or time-dependent) classical field and a monochromatic electromagnetic wave. We discuss the possible medium effects on the rate in the presence of thermal electrons, bosons, and neutral plasma of electrons and protons at a given temperature and chemical potential. Using the rate formula, we shown calculation of the rate enhancement due to a laser beam, and discuss the possibility that a significant enhancement may appear in a plasma of electrons and protons with self-focusing properties.

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