The EGRET sky: a new interstellar emission model and source detection

The comparison of HI, CO, dust, and gamma-ray maps in the solar neighborhood has led to the discovery of large amounts of dark gas. The large mass and angular extent of the local dark clouds, as well as their clumpiness, imply severe revisions of the interstellar emission model to high latitudes, therefore of the detectability of a point-source above the diffuse background. We have used this new model to search for point-like sources at 5\degres$\leq$|b|$_leq$80\degres and we show that numerous persistent unidentified EGRET sources are not confirmed as significant sources

Etude de l'influence des forces de Van der Waals de couleur et d'effets non coulombiens dans la diffusion 208^{208}Pb+208^{208}Pb par une experience de haute precision

This work deals with the precise measurement of the absolute angular position of the elastic 208pb+208pb scattering cross section oscillations. The main objective is to verify if all of the elastic scattering ingredients are known even with an angular position precision of a few milli-degrees or if it is necessary to introduce new elements such as the color van der Waals force. This experiment was performed at Ganil. We obtained a precision of 0.004 deg. on the absolute cross section oscillation position and an angular shift of a few hundredths of degrees in relation to the expected position of a pure coulomb scattering. The attainment of this precision required particular precautions in the measurement of the absolute energy target position and scattering angle. First, the angular straggling on a thin target and the production of δ electrons during the scattering is studied. Next the origin of the angular shift is examined by the calculation of all the potentials that act during the scattering. The agreement between experimentation and theory allowed us to set a new limit on the color van der Waals interaction.Dans ce travail la mesure précise de la position angulaire absolue des oscillations de la section efficace de la diffusion élastique 208Pb+208Pb est étudiée. L'objectif principal est de vérifier si tous les ingrédients d'une diffusion élastique sont connus même lorsque la précision angulaire est de quelques milli-degrés, ou s'il l'on doit introduire des éléments nouveaux comme une force de van der Waals de couleur. L’expérience a été réalisée au GANIL, une précision de 0.004 deg. a été obtenue sur la position absolue des oscillations et un décalage de quelques centièmes de degrés par rapport a la position attendue pour une diffusion purement coulombienne a été observe. L'obtention de cette précision a nécessite des précautions particulières dans la mesure absolue de l’énergie, de la position de la cible et de l'angle de diffusion. Il est d'abord étudie la dispersion angulaire dans une cible mince et la production d’électrons δ lors de la diffusion. Ensuite l'origine du décalage angulaire des oscillations de la section efficace a été étudiée par le calcul de tous les potentiels présents lors de la diffusion. L'accord entre expérience et théorie a permis d'instaurer une nouvelle limite de l'interaction de van der Waals de couleur

Direct evidence of transfer with weakly bound isotopes of He near the Coulomb barrier and implications of fusion

NESTERPartial residue cross sections for fusion and transfer have been measured from the intensities of characteristic gamma-rays for the $^{4,6}$ He + $^{63,65}$Cu systems at energies near the Coulomb barrier (Vb)

High precision position measurements at high counting rates with drift chambers and multi-hit electronics

11 pages, 7 figure

Virtual coupling potential for elastic scattering of 10,11^{10,11}Be on proton and carbon targets

International audienceThe 10;11Be(p,p) and (12C, 12C) reactions were analyzed to determine the in uence of the weak binding energies of exotic nuclei on their interaction potential. The elastic cross sections were measured at GANIL in inverse kinematics using radioactive 10;11Be beams produced at energies of 39:1 A and 38:4A MeV. The elastic proton scattering data were analyzed within the framework of the microscopic Jeukenne-Lejeune-Mahaux (JLM) nucleon-nucleus potential. The angular distributions are found to be best reproduced by reducing the real part of the microscopic optical potential, as a consequence of the coupling to the continuum. These effects modify deeply the elastic potential. Including the Virtual Coupling Potential (VCP), we show the ability of the general optical potentials to reproduce the data for scattering of unstable nuclei, using realistic densities. Finally, the concepts needed to develop a more general and microscopic approach of the VCP are discussed

Coupling effects in the elastic scattering of 6^{6}He on 12^{12}C

To study the effect of the weak binding energy on the interaction potential between a light exotic nucleus and a target, elastic scattering of 6He at 38.3 MeV/nucleon on a 12C target was measured at Grand Accélérateur National d'Ions Lourds (GANIL). The 6He beam was produced by fragmentation. The detection of the scattered particles was performed by the GANIL spectrometer. The energy resolution was good enough to separate elastic from inelastic scattering contributions. The measured elastic data have been analyzed within the optical model, with the real part of the optical potential calculated in the double-folding model using a realistic density-dependent nucleon-nucleon interaction and the imaginary part taken in the conventional Woods-Saxon (WS) form. A failure of the "bare" real folded potential to reproduce the measured angular distribution over the whole angular range suggests quite a strong coupling of the higher-order breakup channels to the elastic channel. To estimate the strength of the breakup effects, a complex surface potential with a repulsive real part (designed to simulate the polarization effects caused by the projectile breakup) was added to the real folded and imaginary WS potentials. A realistic estimate of the polarization potential caused by the breakup of the weakly bound 6He was made based on a parallel study of 6He+12C and 6Li+12C optical potentials at about the same energies

Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope

Nearby clusters and groups of galaxies are potentially bright sources of high-energy gamma-ray emission resulting from the pair-annihilation of dark matter particles. However, no significant gamma-ray emission has been detected so far from clusters in the first 11 months of observations with the Fermi Large Area Telescope. We interpret this non-detection in terms of constraints on dark matter particle properties. In particular for leptonic annihilation final states and particle masses greater than ~200 GeV, gamma-ray emission from inverse Compton scattering of CMB photons is expected to dominate the dark matter annihilation signal from clusters, and our gamma-ray limits exclude large regions of the parameter space that would give a good fit to the recent anomalous Pamela and Fermi-LAT electron-positron measurements. We also present constraints on the annihilation of more standard dark matter candidates, such as the lightest neutralino of supersymmetric models. The constraints are particularly strong when including the fact that clusters are known to contain substructure at least on galaxy scales, increasing the expected gamma-ray flux by a factor of ~5 over a smooth-halo assumption. We also explore the effect of uncertainties in cluster dark matter density profiles, finding a systematic uncertainty in the constraints of roughly a factor of two, but similar overall conclusions. In this work, we focus on deriving limits on dark matter models; a more general consideration of the Fermi-LAT data on clusters and clusters as gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo, minor revisions to be consistent with accepted versio

Charge-exchange reaction with light neutron-rich beams

The charge exchange reaction p(6He, 6Li) was studied in reverse kinematics with a secondary 6He beam at 41.6 MeV/nucleo

DEVELOPMENT of the MODEL of GALACTIC INTERSTELLAR EMISSION for STANDARD POINT-SOURCE ANALYSIS of FERMI LARGE AREA TELESCOPE DATA

Most of the celestial \u3b3 rays detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point-source and extended-source studies rely on the modeling of this diffuse emission for accurate characterization. Here, we describe the development of the Galactic Interstellar Emission Model (GIEM), which is the standard adopted by the LAT Collaboration and is publicly available. This model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse-Compton emission produced in the Galaxy. In the GIEM, we also include large-scale structures like Loop I and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20\ub0 and we observe an enhanced emission toward their base extending in the north and south Galactic directions and located within \u2dc4\ub0 of the Galactic Center

The On-orbit Calibrations for the Fermi Large Area Telescope

The Large Area Telescope (LAT) on--board the Fermi Gamma ray Space Telescope began its on--orbit operations on June 23, 2008. Calibrations, defined in a generic sense, correspond to synchronization of trigger signals, optimization of delays for latching data, determination of detector thresholds, gains and responses, evaluation of the perimeter of the South Atlantic Anomaly (SAA), measurements of live time, of absolute time, and internal and spacecraft boresight alignments. Here we describe on orbit calibration results obtained using known astrophysical sources, galactic cosmic rays, and charge injection into the front-end electronics of each detector. Instrument response functions will be described in a separate publication. This paper demonstrates the stability of calibrations and describes minor changes observed since launch. These results have been used to calibrate the LAT datasets to be publicly released in August 2009.Comment: 60 pages, 34 figures, submitted to Astroparticle Physic