24 research outputs found

    Clusters of Galaxies and the Diffuse Gamma Ray Background

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    We discuss the diffuse emission of gamma rays and neutrinos from galaxy clusters in the viable models for structure formation in the universe. We use a self-consistent picture for cluster formation and evolution starting from a primordial density perturbation spectrum, and a realistic modelling for the distribution of the intergalactic medium which is abundantly present within galaxy clusters. We find that an evolving population of clusters can produce a fraction 0.5÷2\sim 0.5 \div 2 % of the diffuse gamma-ray background (DGRB) observed by EGRET. This result is robust and is weakly dependent on the cosmological scenario and on the degree of evolution of the inter galactic medium (IGM) in distant clusters, because the bulk of the sources contributing to the DGRB is located at redshifts z \simlt 0.2. We also found a correlation between the non-thermal, gamma-ray and the thermal X-ray emissions from these structures. Using this result, we derived a list of gamma-ray clusters observable with the next generation γ\gamma-ray detectors. Finally, we briefly discuss the possible relevance of galaxy clusters for neutrino astronomy and for very high energy particle astronomy.Comment: 37 pages, 9 Figures, Latex (using elsart,epsfig), to appear in Astroparticle Physics. Send comments to S.Colafrancesco: [email protected]

    Peculiarities and variations in the optical spectrum of the post-AGB star V448Lac=IRAS22223+4327

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    Repeated observations with high spectral resolution acquired in 1998-2008 are used to study the temporal behavior of the spectral line profiles and velocity field in the atmosphere and circumstellar envelope of the post-AGB star V448Lac. Asymmetry of the profiles of the strongest absorption lines with low-level excitation potentials less 1eV and time variations of these profiles have been detected, most prominently the profiles of the resonance lines of BaII, YII, LaII, SiII. The peculiarity of these profiles can be explained using a superposition of stellar absorption line and shell emission lines. Emission in the (0;1) 5635A Swan band of the C2 molecule has been detected in the spectrum of V448Lac for the first time. The core of the Halpha line displays radial velocity variations with an amplitude ~8 km/s. Radial velocity variations displayed by weakest metallic lines with lower amplitudes, 1-2 km/s, may be due to atmospheric pulsations. Differential line shifts, 0 -- 8 km/s, have been detected on various dates. The position of the molecular spectrum is stationary in time, indicating a constant expansion velocity of the circumstellar shell, Vexp=15.2 km/s, as derived from the C2 and NaI lines.Comment: 19 pages, 8 figures, 1 tabl

    New Spectroscopic Observations of the Post-AGB Star V354Lac=IRAS22272+5435

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    The strongest absorption features with the lower-level excitation potentials χlow<1\chi_{\rm low}<1 eV are found to be split in the high-resolution optical spectra of the post-AGB star V354 Lac taken in 2007--2008. Main parameters, Teff_{eff}=5650 K, logg\log g=0.2, ξt\xi_t=5.0 km/s, and the abundances of 22 chemical elements in the star's atmosphere are found. The overabundance of the ss-process chemical elements (Ba, La, Ce, Nd) in the star's atmosphere is partly due to the splitting of strong lines of the ions of these metals. The peculiarities of the spectrum in the wavelength interval containing the LiI λ\lambda 6707 \AA{} line can be naturally explained only by taking the overabundances of the CeII and SmII heavy-metal ions into account. The best agreement with the synthetic spectrum is achieved assuming ϵ\epsilon(LiI)=2.0, ϵ\epsilon(CeII)=3.2, and ϵ\epsilon(SmII)=2.7. The velocity field both in the atmosphere and in the circumstellar envelope of V354 Lac remained stationary throughout the last 15 years of our observations.Comment: 16 pages, 6 figures, 2 table

    The Antares Collaboration : Contributions to the 34th International Cosmic Ray Conference (ICRC 2015, The Hague)

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    The ANTARES detector, completed in 2008, is the largest neutrino telescope in the Northern hemisphere. Located at a depth of 2.5 km in the Mediterranean Sea, 40 km off the Toulon shore, its main goal is the search for astrophysical high energy neutrinos. In this paper we collect the 21 contributions of the ANTARES collaboration to the 34th International Cosmic Ray Conference (ICRC 2015). The scientific output is very rich and the contributions included in these proceedings cover the main physics results, ranging from steady point sources, diffuse searches, multi-messenger analyses to exotic physics

    The Bologna complete sample of nearby radio sources: II -- phase referenced observations of faint nuclear sources

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    To study statistical properties of different classes of sources, it is necessary to observe a sample that is free of selection effects. To do this, we initiated a project to observe a complete sample of radio galaxies selected from the B2 Catalogue of Radio Sources and the Third Cambridge Revised Catalogue (3CR), with no selection constraint on the nuclear properties. We named this sample "the Bologna Complete Sample" (BCS). We present new VLBI observations at 5 and 1.6 GHz for 33 sources drawn from a sample not biased toward orientation. By combining these data with those in the literature, information on the parsec-scale morphology is available for a total of 76 of 94 radio sources with a range in radio power and kiloparsec-scale morphologies. The fraction of two-sided sources at milliarcsecond resolution is high (30%), compared to the fraction found in VLBI surveys selected at centimeter wavelengths, as expected from the predictions of unified models. The parsec-scale jets are generally found to be straight and to line up with the kiloparsec-scale jets. A few peculiar sources are discussed in detail.Comment: 19 pages, 1 colour figure. Accepted for the publication in Astronomy and Astrophysic

    Multilepton Events and H++ Searches at HERA

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    Measurement of D* Production in Diffractive Deep Inelastic Scattering at HERA

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    See paper for full list of authors - 28 pages, 8 figures, to be submitted to EPJ CInternational audienceMeasurements of D(2010)D^{*}(2010) meson production in diffractive deep inelastic scattering (5<Q2<100 GeV2)(5<Q^{2}<100~{\rm GeV}^{2}) are presented which are based on HERA data recorded at a centre-of-mass energy s=319 GeV\sqrt{s} = 319{\rm~GeV} with an integrated luminosity of 287287 pb1^{-1}. The reaction epeXYep \rightarrow eXY is studied, where the system XX, containing at least one D(2010)D^{*}(2010) meson, is separated from a leading low-mass proton dissociative system YY by a large rapidity gap. The kinematics of DD^{*} candidates are reconstructed in the DKππD^{*}\rightarrow K \pi\pi decay channel. The measured cross sections compare favourably with next-to-leading order QCD predictions, where charm quarks are produced via boson-gluon fusion. The charm quarks are then independently fragmented to the DD^{*} mesons. The calculations rely on the collinear factorisation theorem and are based on diffractive parton densities previously obtained by H1 from fits to inclusive diffractive cross sections. The data are further used to determine the diffractive to inclusive DD^{*} production ratio in deep inelastic scattering
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