3,203 research outputs found

    An Analysis of Contextual Effects on Electoral Behavior.

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    The Minimal Supersymmetric Standard Model: Group Summary Report

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    CONTENTS: 1. Synopsis, 2. The MSSM Spectrum, 3. The Physical Parameters, 4. Higgs Boson Production and Decays, 5. SUSY Particle Production and Decays, 6. Experimental Bounds on SUSY Particle Masses, 7. References.Comment: 121 pages, latex + epsfig, graphicx, axodraw, Report of the MSSM working group for the Workshop "GDR-Supersym\'etrie",France. Rep. PM/98-4

    Search for Early Gamma-ray Production in Supernovae Located in a Dense Circumstellar Medium with the Fermi LAT

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    Supernovae (SNe) exploding in a dense circumstellar medium (CSM) are hypothesized to accelerate cosmic rays in collisionless shocks and emit GeV gamma rays and TeV neutrinos on a time scale of several months. We perform the first systematic search for gamma-ray emission in Fermi LAT data in the energy range from 100 MeV to 300 GeV from the ensemble of 147 SNe Type IIn exploding in dense CSM. We search for a gamma-ray excess at each SNe location in a one year time window. In order to enhance a possible weak signal, we simultaneously study the closest and optically brightest sources of our sample in a joint-likelihood analysis in three different time windows (1 year, 6 months and 3 months). For the most promising source of the sample, SN 2010jl (PTF10aaxf), we repeat the analysis with an extended time window lasting 4.5 years. We do not find a significant excess in gamma rays for any individual source nor for the combined sources and provide model-independent flux upper limits for both cases. In addition, we derive limits on the gamma-ray luminosity and the ratio of gamma-ray-to-optical luminosity ratio as a function of the index of the proton injection spectrum assuming a generic gamma-ray production model. Furthermore, we present detailed flux predictions based on multi-wavelength observations and the corresponding flux upper limit at 95% confidence level (CL) for the source SN 2010jl (PTF10aaxf).Comment: Accepted for publication in ApJ. Corresponding author: A. Franckowiak ([email protected]), updated author list and acknowledgement

    Search for extended gamma-ray emission from the Virgo galaxy cluster with Fermi-LAT

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    Galaxy clusters are one of the prime sites to search for dark matter (DM) annihilation signals. Depending on the substructure of the DM halo of a galaxy cluster and the cross sections for DM annihilation channels, these signals might be detectable by the latest generation of ő≥\gamma-ray telescopes. Here we use three years of Fermi Large Area Telescope (LAT) data, which are the most suitable for searching for very extended emission in the vicinity of nearby Virgo galaxy cluster. Our analysis reveals statistically significant extended emission which can be well characterized by a uniformly emitting disk profile with a radius of 3\deg that moreover is offset from the cluster center. We demonstrate that the significance of this extended emission strongly depends on the adopted interstellar emission model (IEM) and is most likely an artifact of our incomplete description of the IEM in this region. We also search for and find new point source candidates in the region. We then derive conservative upper limits on the velocity-averaged DM pair annihilation cross section from Virgo. We take into account the potential ő≥\gamma-ray flux enhancement due to DM sub-halos and its complex morphology as a merging cluster. For DM annihilating into bb‚Äĺb\overline{b}, assuming a conservative sub-halo model setup, we find limits that are between 1 and 1.5 orders of magnitude above the expectation from the thermal cross section for mDM‚Č≤100‚ÄČGeVm_{\mathrm{DM}}\lesssim100\,\mathrm{GeV}. In a more optimistic scenario, we exclude ‚ü®ŌÉv‚ü©‚ąľ3√ó10‚ąí26‚ÄČcm3‚ÄČs‚ąí1\langle \sigma v \rangle\sim3\times10^{-26}\,\mathrm{cm^{3}\,s^{-1}} for mDM‚Č≤40‚ÄČGeVm_{\mathrm{DM}}\lesssim40\,\mathrm{GeV} for the same channel. Finally, we derive upper limits on the ő≥\gamma-ray-flux produced by hadronic cosmic-ray interactions in the inter cluster medium. We find that the volume-averaged cosmic-ray-to-thermal pressure ratio is less than ‚ąľ6%\sim6\%.Comment: 15 pages, 11 figures, 4 tables, accepted for publication in ApJ; corresponding authors: T. Jogler, S. Zimmer & A. Pinzk

    Constraints on dark matter models from a Fermi LAT search for high-energy cosmic-ray electrons from the Sun

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    During its first year of data taking, the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy cosmic-ray electrons and positrons (CREs). We present the results of a directional analysis of the CRE events, in which we searched for a flux excess correlated with the direction of the Sun. Two different and complementary analysis approaches were implemented, and neither yielded evidence of a significant CRE flux excess from the Sun. We derive upper limits on the CRE flux from the Sun's direction, and use these bounds to constrain two classes of dark matter models which predict a solar CRE flux: (1) models in which dark matter annihilates to CREs via a light intermediate state, and (2) inelastic dark matter models in which dark matter annihilates to CREs.Comment: 18 pages, 8 figures, accepted for publication in Physical Review D - contact authors: Francesco Loparco ([email protected]), M. Nicola Mazziotta ([email protected]) and Jennifer Siegal-Gaskins ([email protected]

    Improved outcomes of pediatric dilated cardiomyopathy with utilization of heart transplantation

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    AbstractObjectivesWe studied the outcomes of pediatric patients diagnosed with dilated cardiomyopathy (DCM) and their relation to epidemiologic and echocardiographic variables at the time of presentation.BackgroundThe outcome of pediatric DCM patients ranges from recovery to a 50% to 60% chance of death within five years of diagnosis. The impact of heart transplantation and other emerging therapies on the outcomes of pediatric DCM patients is uncertain.MethodsWe performed a retrospective study of the outcomes in 91 pediatric patients diagnosed with DCM from 1990 to 1999. Routine therapy included use of digoxin, diuretics, angiotensin-converting enzyme inhibitors, and heart transplantation.ResultsAt the time of last follow-up, 11 patients (12%) had died without transplantation; 20 (22%) underwent transplantation; 27 (30%) had persistent cardiomyopathy; and 33 (36%) had recovery of left ventricular systolic function. Overall actuarial one-year survival was 90%, and five-year survival was 83%. However, actuarial freedom from ‚Äúheart death‚ÄĚ (death or transplantation) was only 70% at one year and 58% at five years. Multivariate analysis found age <1 year (hazard ratio 7.1), age >12 years (hazard ratio 4.5), and female gender (hazard ratio 3.0) to be significantly associated with a greater risk of death or transplantation and a higher left ventricular shortening fraction at presentation (hazard ratio 0.92), with a slightly decreased risk of death or transplantation.ConclusionsPediatric DCM patients continue to have multiple outcomes, with recovery of left ventricular systolic function occurring most frequently. Utilization of heart transplantation has led to improved survival after the diagnosis of pediatric DCM

    Gamma-ray flaring activity from the gravitationally lensed blazar PKS 1830-211 observed by Fermi LAT

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    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope routinely detects the highly dust-absorbed, reddened, and MeV-peaked flat spectrum radio quasar PKS 1830-211 (z=2.507). Its apparent isotropic gamma-ray luminosity (E>100 MeV) averaged over ‚ąľ\sim 3 years of observations and peaking on 2010 October 14/15 at 2.9 X 10^{50} erg s^{-1}, makes it among the brightest high-redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time delayed variability to follow about 25 days after a primary flare, with flux about a factor 1.5 less. Two large gamma-ray flares of PKS 1830-211 have been detected by the LAT in the considered period and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the gamma rays flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum and with no significant correlation of X-ray flux with the gamma-ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and gamma-ray flux ratios are discussed. Microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy-dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results.Comment: 14 pages, 6 figures, 2 tables. Accepted by the The Astrophysical Journal. Corresponding authors: S. Ciprini (ASI ASDC & INAF OAR, Rome, Italy), S. Buson (INAF Padova & Univ. of Padova, Padova, Italy), J. Finke (NRL, Washington, DC, USA), F. D'Ammando (INAF IRA, Bologna, Italy

    Fermi-LAT observations of the exceptional gamma-ray outbursts of 3C 273 in September 2009

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    We present the light curves and spectral data of two exceptionally luminous gamma-ray outburts observed by the Large Area Telescope (LAT) experiment on board Fermi Gamma-ray Space Telescope from 3C 273 in September 2009. During these flares, having a duration of a few days, the source reached its highest gamma-ray flux ever measured. This allowed us to study in some details their spectral and temporal structures. The rise and decay are asymmetric on timescales of 6 hours, and the spectral index was significantly harder during the flares than during the preceding 11 months. We also found that short, very intense flares put out the same time-integrated energy as long, less intense flares like that observed in August 2009.Comment: Corresponding authors: E. Massaro, [email protected]; G. Tosti, [email protected]. 15 pages, 4 figures, published in The Astrophysical Journal Letters, Volume 714, Issue 1, pp. L73-L78 (2010

    Fermi Large Area Telescope Observations of the Cosmic-Ray Induced gamma-ray Emission of the Earth's Atmosphere

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    We report on measurements of the cosmic-ray induced gamma-ray emission of Earth's atmosphere by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. The LAT has observed the Earth during its commissioning phase and with a dedicated Earth-limb following observation in September 2008. These measurements yielded 6.4 x 10^6 photons with energies >100MeV and ~250hours total livetime for the highest quality data selection. This allows the study of the spatial and spectral distributions of these photons with unprecedented detail. The spectrum of the emission - often referred to as Earth albedo gamma-ray emission - has a power-law shape up to 500 GeV with spectral index Gamma = 2.79+-0.06.Comment: Accepted for publication in PR

    Fermi Gamma-ray Space Telescope Observations of the Gamma-ray Outburst from 3C 454.3 in November 2010

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    The flat-spectrum radio quasar 3C 454.3 underwent an extraordinary 5-day gamma-ray outburst in November 2010 where the daily flux measured with the Fermi Large Area Telescope (LAT) at photon energies E>100 MeV reached (66+/-2) x 10^-6 ph cm^-2 s^-1. This is a factor of 3 higher than its previous maximum flux recorded in December 2009 and ~5 times brighter than the Vela pulsar, which is normally the brightest source in the gamma-ray sky. The 3-hr peak flux was (85+/-5) x 10^-6 ph cm^-2 s^-1, corresponding to an apparent isotropic luminosity of 2.1+/-0.2 10^50 erg s^-1, the highest ever recorded for a blazar. In this paper, we investigate the features of this exceptional event in the gamma-ray band of the Fermi-LAT. In contrast to previous flares of the same source observed with the Fermi-LAT, clear spectral changes are observed during the flare.Comment: Contact authors: Lise Escande, Charles Dermer and Benoit Lott. One new figure. Accepted for publication by ApJ
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