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Session PCHE

HLX-1 in ESO 243-49: the strongest evidence for the existence of Intermediate Mass Black Holes
O. Godet, D. Barret, N. Webb & B. Plazolles (CESR), S. Farrell, K. Wiersema (University of Leicester, UK), T. Maccarone (University of Southampton, UK), M. Servillat (Harvard-Smithsonian CfA, USA), S. Oates (MSSL, UK), I. Heywood (University of Oxford, UK)

Fundamental physics in observational cosmology
P. Peter
Observational cosmology has now become accurate enough that fundamental physics effects are becoming measurable. For instance, high energy particle theories may produce topological defects, or modify the light dispersion relation around the Planck scale, or more generically break the Lorentz invariance over ver large scales. The evolution of the Universe can also be rather different from what the usual paradigm states it is, as, in particular, it can have experienced a contracting phase bouncing to the currently expanding one; this not only takes place in loop quantum cosmology, as is often stated, but also in string based models (e.g. the pre big bang) or in plain quantum cosmology using the Wheeler de Witt formulation.

Latest results on Galactic SNRs in the gamma-ray domain
M. Renaud
(Laboratoire de Physique Théorique et Astroparticules)
Latest results on Galactic SNRs as seen in the gamma-ray domain, mainly with Fermi and the current generation of Cherenkov telescopes, are reviewed. From the youngest isolated SNRs to the more evolved ones interacting with the surrounding medium, these observations provide new insights into the long-standing question of sources at the origin of Galactic cosmic-rays.

Towards new analysis of Gamma-Ray sources with the HAGAR telescope array in the Indian Himalayas
Richard J. Britto (on behalf of HAGAR collaboration)
(Tata Institute of Fundamental Research)
The High Altitude GAmma-Ray (HAGAR) array is a wavefront sampling array of 7 telescopes, set-up at Hanle, at 4270 m amsl, in the Ladakh region of the Himalayas (North India). It constitutes the first phase of the HImalayan Gamma-Ray Observatory (HIGRO) project. HAGAR is the first array of atmospheric Cherenkov telescopes established at a so high altitude, and was designed to reach a relatively low threshold (currently around 200 GeV) with quite a low mirror area (31 m$^2$). Data are acquired using the On-source/Off-source tracking mode, and by comparing these sky regions the strength of the gamma-ray signal is estimated. Regular source observations are running since Sept. 2008 and preliminary results on Crab nebula were reported by 2009. Improvements of our analysis method are still going on, like estimation of arrival direction and estimation of night sky background. New softwares are under development for analysis of flash ADC modules, which provide more information from the incoming Cherenkov light wavefront. We report and discuss our new estimation of the systematics through dark region studies, and present new preliminary results from gamma-ray sources, etc., in this paper.

High-energy radiation from the relativistic jet of Cygnus X-3
Benoît Cerutti, Guillaume Dubus, Gilles Henri
(Laboratoire d'astrophysique de Grenoble)
Cygnus X-3 is an accreting high-mass X-ray binary composed of a Wolf-Rayet star and an unknown compact object, possibly a black hole. The gamma-ray space telescopes AGILE and Fermi found the definitive evidence that high-energy emission is produced in this system. We propose a scenario to explain the GeV gamma-ray emission in Cygnus X-3. In this model, energetic electron-positron pairs are accelerated at a specific location in the relativistic jet, possibly related to a recollimation shock, and upscatter the stellar photons to high energies. The comparison with Fermi observations shows that the jet should be inclined close to the line of sight and that pairs should not be located within the system. Energetically speaking, a massive compact object is favored. We report also on our investigations of the gamma-ray absorption of GeV photons with the radiation emitted by a standard accretion disk in Cygnus X-3. This study shows that the gamma-ray source should not lie to close to the compact object.

Large scale magnetic field variability in accretion discs.
Rémi de Guiran, Jonathan Ferreira.
Accretion discs are composed of ionized gas in motion around a central object. Sometimes, the disc is the source of powerful bipolar jets along its rotation axis. Theoretical models invoke the existence of a bipolar magnetic field crossing the disc and require two conditions to produce powerful jets: field lines need to be bended enough at the surface of the disc and the magnetic field needs to be close to equipartition. The work of Petrucci et al (2008) on the variability of X-ray binaries supposes that transitions between pure accretion phases and accretion-ejection phases are due to some variations of the magnetization. This rises the problem of the magnetic field dragging in accretion discs. We revisit the method developed by Lubow et al (1994), coupling it with momentum and mass conservation in a 1D MHD code. Considering a variability of the accretion rate at the external radius of the disc, we show the consequences of such a transport on the behaviour of magnetization, and its possible implications on the dynamic of the disc.

Contribution of phonons to the thermal properties of the neutron star crust
Di Gallo Luc & Oertel Micaela
(Luth (Observatoire de Paris))
Neutron stars are compact objects, created in supernova explosions at the end of the life of massive stars. They contain matter under extreme conditions, in particular concerning the density : starting from a lattice of (neutron rich) nuclei in the crust one reaches nuclear matter at several times the density of atomic nuclei in the center. One way to understand this object is to do theoretical modelisation in confrontation to observations. Among observations of pulsars there is the thermal emission of its surface. This observable, which depend on the heat transport properties, is very sensitive to the superfluid and superconducting character of the different sutructures inside the star. I focus my presentation on the inner crust, where we can find an interesting nuclear structure called the "Pasta Phase". Within a superfluid hydrodynamics approach I will discuss its excitation spectrum and the influence on the heat capacity.

Search for neutrinos from transient sources with the ANTARES telescope and optical follow-up observations
D. Dornic
(IFIC- Valencia)
The ANTARES telescope has the opportunity to detect transient neutrino sources, such as gamma-ray bursts, core-collapse supernovae, flares of active galactic nuclei... In order to enhance the sensitivity to these sources, we have developed a new detection method based on the follow-up by optical telescopes of ``golden'' neutrino events such as neutrino doublets coincident in time and space or single neutrinos of very high energy.

The ANTARES collaboration has therefore implemented a very fast on-line reconstruction with a good angular resolution. These characteristics allow us to trigger an optical telescope network. Since February 2009, ANTARES is sending alert triggers one or twice per month to the six robotic telescope of TAROT and ROTSE . This optical follow-up of such special events would not only give access to the nature of the sources but also would improve the sensitivity to transient neutrino sources.

Fermi Gamma-ray Space Telescope observations of recent gamma-ray outbursts of 3C 454.3
Lise Escande
(Université Bordeaux 1, CNRS/IN2P3, CENBG)
The flat spectrum radio quasar 3C 454.3 underwent an extraordinary outburst in December 2009 when it became the brightest gamma-ray source in the sky for over one week. Its daily flux measured with the Fermi Large Area Telescope at photon energies E>100MeV reached 22x10-6 ph/cm2/s, representing the highest daily flux of any blazar ever recorded in high-energy gamma-rays. It again became the brightest source in the sky in April 2010, triggering a pointed-mode observation by Fermi. The gamma-ray temporal and spectral properties during these exceptional events will be presented and discussed.

recent results of the FIGARO collaboration
B. Gendre, A. Corsi, G. Stratta, A. Klotz, J.L. Atteia, M. Boer, S. Cutini, F. Daigne, R. Mochkovitch, L. Piro
The FIGARO collaboration aims are to study the early phase of the gamma ray burst afterglows and the prompt-to-afterglow transition phase, using multi-wavelength observations (mostly from Swift and TAROT). Here, we review the recent results of the collaboration, including the discovery of a rising part of the optical light curve and its theoretical interpretation (text in french).

AMS un detecteur de physique des particules dans l'espace.
Corinne Goy
Thanks to its ability to identify and to measure simultaneously fluxes of protons, antiprotons, electrons, positrons, gamma rays and nuclei in a large acceptance detector and on an extended energy range, AMS will improve the knowledge of standard mecanisms governing the propagation of cosmic rays and will probe the existence of new physics, such as the nature of Dark Matter. The status of AMS, a few months away from its launch and installation on the Space Station in the second half of 2010, will be presented

Core collapse supernovae : Effect of the magnetic field on fluid motions
Jérôme Guilet, Thierry Foglizzo, Sébastien Fromang
(CEA - Saclay)
Multidimensional fluid motions play an essential role in the dynamics of core collapse supernovae. We investigate how this fluid dynamics is affected by a large scale magnetic field. In particular, we consider the shock oscillations caused by the standing accretion shock instability. These oscillations create Alfvén waves that are amplified at the so called Alfvén surface (where the Alfvén speed equals the advection velocity) and we study the consequences of this amplification.

Lorentz Symmetry and Quantum Gravity with astrophysical sources
A. Jacholkowska
Lorentz Invariance Violation (LIV) is a good observational window on Quantum Gravity models. Within last few years, all major Gamma-ray experiments have published results from the search for LIV with variable astrophysical sources: Gamma-ray Bursts with detectors on-board satellites and Active Galactic Nuclei with ground-based experiments. In addition, most of future experiments (SVOM, CTA and others) put the search for LIV in their main physics goals. As the latest results tend to disfavour first order effects with energy, excluding a whole set of models based on space-time "foam", it is possible that the whole theoretical landscape will change in the next years. In light of these exciting new results, a status report about both the theoretical and observational aspects will be presented.

Simulation of black hole formation in stellar collapse
J. Novak, M. Oertel, B. Peres
(LUTH, CNRS - Observatoire de Paris)
The collapse of massive stars leads in principle to the formation of a black hole with possible observables, from gamma-rays to neutrinos and gravitational waves. The complex physics involved in this phenomenon require the use of numerical models. We here present a starting project, based on the code CoCoNuT, to perform realistic studies in full general relativity and with detailed microphysics, of the collapse of a rotating stellar core to a black hole.

An extended equation of state for simulations of stellar collapse
M. Oertel, A. Fantina
(LUTH, CNRS-Observatoire de Paris)
In core-collapse events matter is heated and compressed to densities above nuclear matter saturation density. For progenitors with masses above $\sim$25 solar masses, which eventually form a black hole, the temperatures and densities reached during the collapse are so high that a traditional description in terms of electrons, nuclei, and nucleons is no longer adequate. We will present here an improved equation of state which contains in addition pions and hyperons. They become abundant in the high temperature and density regime, and we will discuss the effect on the thermodynamic properties.

High energy emission from compact objects: observation, modelisation and theory
After a short introduction of the main characteristics of the high energy emission of compact objects (AGN, microquasars), and the different research topics in which our group is involved, I will focus on two of them: 1) the development of a accretion-ejection model and its application to microquasars and 2) the first results of the long (10 days) multi wave-length (from optical to soft gamma-rays) monitoring of the Seyfert galaxy Mkn 509.

Gamma-Ray Burst Observations with Fermi
F. Piron, on behalf of the GBM and LAT collaborations

Coincident searches for neutrinos and gravitational waves with the ANTARES and LIGO/VIRGO detectors
V. Van Elewyck for the GWHEN group [ANTARES & VIGO/LIGO Coll.]
Both gravitational waves (GW) and high-energy neutrinos (HEN) are cosmic messengers that may escape very dense media and travel unaffected over cosmological distances, carrying information from the innermost regions of the astrophysical engines. For the same reasons, such messengers could also reveal new, hidden sources that were not observed by conventional photon astronomy. In this talk I will describe the strategies for coincident searches of GW and HEN from astrophysical sources that are currently developed by the ANTARES and VIRGO/LIGO collaborations within the GWHEN working group.

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suivant: Poster contributions monter: sf2a_boa précédent: Poster contributions
Samuel Boissier 2010-06-16