Pulsar Wind Nebulae as a source of the observed electron and positron excess at high energy: the case of Vela-X

We investigate, in terms of production from pulsars and their nebulae, the cosmic ray positron and electron fluxes above $\sim10$ GeV, observed by the AMS-02 experiment up to 1 TeV. We concentrate on the Vela-X case. Starting from the gamma-ray photon spectrum of the source, generated via synchrotron and inverse Compton processes, we estimated the electron and positron injection spectra. Several features are fixed from observations of Vela-X and unknown parameters are borrowed from the Crab nebula. The particle spectra produced in the pulsar wind nebula are then propagated up to the Solar System, using a diffusion model. Differently from previous works, the omnidirectional intensity excess for electrons and positrons is obtained as a difference between the AMS-02 data and the corresponding local interstellar spectrum. An equal amount of electron and positron excess is observed and we interpreted this excess (above $\sim$100 GeV in the AMS-02 data) as a supply coming from Vela-X. The particle contribution is consistent with models predicting the gamma-ray emission at the source. The input of a few more young pulsars is also allowed, while below $\sim$100 GeV more aged pulsars could be the main contributors.Comment: Accepted for publication in Journal of High Energy Astrophysics (2015

The cool core state of Planck SZ-selected clusters versus X-ray selected samples: evidence for cool core bias

We characterized the population of galaxy clusters detected with the SZ effect with Planck, by measuring the cool core state of the objects in a well-defined subsample of the Planck catalogue. We used as indicator the concentration parameter Santos et al. (2008). The fraction of cool core clusters is $29 \pm 4 \%$ and does not show significant indications of evolution in the redshift range covered by our sample. We compare the distribution of the concentration parameter in the Planck sample with the one of the X-ray selected sample MACS (Mann & Ebeling, 2011): the distributions are significantly different and the cool core fraction in MACS is much higher ($59 \pm 5 \%$). Since X-ray selected samples are known to be biased towards cool cores due to the presence of their prominent surface brightness peak, we simulated the impact of the "cool core bias" following Eckert et al. (2011). We found that it plays a large role in the difference between the fractions of cool cores in the two samples. We examined other selection effects that could in principle bias SZ-surveys against cool cores but we found that their impact is not sufficient to explain the difference between Planck and MACS. The population of X-ray under-luminous objects, which are found in SZ-surveys but missing in X-ray samples (Planck Collaboration 2016), could possibly contribute to the difference, as we found most of them to be non cool cores, but this hypothesis deserves further investigation.Comment: Accepted for publication in MNRA

Numération bactérienne en épifluorescence par la méthode couplée DAPI-INT : application à un cas concret

Un protocole simple de coloration par la méthode couplée DAPI-INT en microscopie à épifluorescence, associé à une lecture des préparations par caméra et vidéo-Imprimante, permet la mesure de paramètres biologiques impliqués directement dans les processus de dégradation de la matière organique en rivière : numérations de microflore totale, nombre de cellules physiologiquement actives (réduisant l'INT), nombre de cellules avec réserves de PHB, dimensions cellulaires et répartition en classes de taille aboutissant à l'évaluation de la biomasse carbonée.Tous les comptages et mesures sont réalisés à partir de clichés d'imprimante thermique, ce qui assure une reproductibilité et une comparaison entre échantillons plus objective qu'à partir de seules observations directes.Cette méthode permet de différer soit les comptages (échantillons fixés au formol après incubation à l'INT), soit surtout les mesures de dimensions cellulaires (archivage des clichés pour une exploitation ultérieure).Son application au cas de la rivière Charente montre une évolution particulière de la biomasse bactérienne en aval des rejets de l'agglomération d'Angoulême. La mise en évidence de cellules de grande taille (biovolume moyen de 0,3 µm3) et d'une population plus active pourrait traduire une modification physiologique de micro-organismes autochtones réagissant à des conditions de milieu particulières (rejets d'effluents carencés en azote).The increasing appreciation of heterotrophic bacterioplankton as an important and dynamic compartment in the carbon cycle of aquatic ecosystems has led to the development of methods allowing reproducible and reliable direct bacterial counts. Thus, since the 1970's, enumeration of bacteria by epifluorescence microscopy has become a widely used method for the estimation of cell number and biovolume. Cell counts are made using either the acridine orange (Hobbie et al. 1977) or the DAPI (Porter 1980) procedure on fixed samples. A tracer of cellular respiratory activity (INT) can be linked to either of these two methods before the samples are killed by formalin. Two observations of the same field, one in transmitted light, the other by epifluorescence, allow a determination of the percentage of active bacterioplankton (Tabor and Neihof 1982, Dufour 1990).However, the various authors working with these procedures have modified the protocol and up to now there has not been a standard method. Thus, before using it for the first time, numerous verifications about filters, concentration of dye solution and methods for estimating cell volume are necessary.In this study a simultaneous comparison, between three brands of filters, two dye solutions and three methods for numeration and cell volume estimation (by direct count, by photographs and by video graphic printer) has been performed.All the tests have been clone with samples collected from rivera or lakes. In comparison to laboratory cultures, natural bacteria are observed with difficulty on account of their small size and especially because natural organic matter absorbs dye solution and so interferes with counts. We prefer to use DAPI rather than acridine orange, because DAPI is colorless in direct light, so it doesn't interfere with enumeration of respiring bacteria (red crystal inside cell). To obtain the best contrast for observation in epifluorescence microscopy, a very fast drying in the open air and a structure less troublesome for the observation in direct light, we have chosen Millipore black filters. A camera associated with a video printer gives better results compared to the photographs : no fluorescent "halo" around the tell image and no waste of time waiting for development of the film. All counts and measures were made from video graphic printer photographs, which assures reproductibility and more objective comparisons between samples, compared to direct counts (with eyes) that are tiring and subjective. Finally, we can defer counting (samples fixed in formol after INT incubation) or cell size measurements (analysis of recorded photos) to a later time.On the basis of this tests, the DAPI-INT method in fluorescence microscopy, associated with the reading of slides with a camera and a video-printer, allows one to measure biological parameters directly implicated in the degradation of river organic matter : abundance of total microflora, number of physiologically active cells (reducing INT) and cells with PHB reserves, cell sizes and size range distribution used to evaluate carbon biomass.The application of this method to the river Charente (April to November 1991) shows a particular fate of bacterial biomass downstream from the city of Angouleme. A multifactor analysis of variance with a multiple range analyses (Tukey) shows that bacterial cells collected downstream from the effluent discharge of the Angouleme wastewater treatment plant are the largest (average cell volume up to 0.3 µm3) and the more active cells. Similar trends have also been observed by Servais and Garnier (1989) downstream from the Paris wastewater treatment plant (Achères) on the Seine river. These authors suggested that allochtonous populations associated with the urban sewage were different from the autochtonous populations (higher biovolume). To verify this hypothesis, a sampling campaign (June 92) was performed on five stations along an eight kilometers river reach. There weren't large size bacteria downstream from the effluent discharge of Frégeneuil, Fléac and St Michel wastewater treatment plants. We Pound the largest bacteria at Nersac. Thus it seems that these large bacteria don't came from wastewater treatment plant. The increase of autochtonous bacterial size could be interpretated as a nutritional stress, the increase of the C/N ratio preventing cellular division (nitrogen deficient sewages)

Antiproton modulation in the Heliosphere and AMS-02 antiproton over proton ratio prediction

We implemented a quasi time-dependent 2D stochastic model of solar modulation describing the transport of cosmic rays (CR) in the heliosphere. Our code can modulate the Local Interstellar Spectrum (LIS) of a generic charged particle (light cosmic ions and electrons), calculating the spectrum at 1AU. Several measurements of CR antiparticles have been performed. Here we focused our attention on the CR antiproton component and the antiproton over proton ratio. We show that our model, using the same heliospheric parameters for both particles, fit the observed anti-p/p ratio. We show a good agreement with BESS-97 and PAMELA data and make a prediction for the AMS-02 experiment

Point defects on graphene on metals

Understanding the coupling of graphene with its local environment is critical to be able to integrate it in tomorrow's electronic devices. Here we show how the presence of a metallic substrate affects the properties of an atomically tailored graphene layer. We have deliberately introduced single carbon vacancies on a graphene monolayer grown on a Pt(111) surface and investigated its impact in the electronic, structural and magnetic properties of the graphene layer. Our low temperature scanning tunneling microscopy studies, complemented by density functional theory, show the existence of a broad electronic resonance above the Fermi energy associated with the vacancies. Vacancy sites become reactive leading to an increase of the coupling between the graphene layer and the metal substrate at these points; this gives rise to a rapid decay of the localized state and the quenching of the magnetic moment associated with carbon vacancies in free-standing graphene layers

Classification of Generalized Symmetries for the Vacuum Einstein Equations

A generalized symmetry of a system of differential equations is an infinitesimal transformation depending locally upon the fields and their derivatives which carries solutions to solutions. We classify all generalized symmetries of the vacuum Einstein equations in four spacetime dimensions. To begin, we analyze symmetries that can be built from the metric, curvature, and covariant derivatives of the curvature to any order; these are called natural symmetries and are globally defined on any spacetime manifold. We next classify first-order generalized symmetries, that is, symmetries that depend on the metric and its first derivatives. Finally, using results from the classification of natural symmetries, we reduce the classification of all higher-order generalized symmetries to the first-order case. In each case we find that the generalized symmetries are infinitesimal generalized diffeomorphisms and constant metric scalings. There are no non-trivial conservation laws associated with these symmetries. A novel feature of our analysis is the use of a fundamental set of spinorial coordinates on the infinite jet space of Ricci-flat metrics, which are derived from Penrose's ``exact set of fields'' for the vacuum equations.Comment: 57 pages, plain Te

Latitudinal Dependence of Cosmic Rays Modulation at 1 AU and Interplanetary-Magnetic-Field Polar Correction

The cosmic rays differential intensity inside the heliosphere, for energy below 30 GeV/nuc, depends on solar activity and interplanetary magnetic field polarity. This variation, termed solar modulation, is described using a 2-D (radius and colatitude) Monte Carlo approach for solving the Parker transport equation that includes diffusion, convection, magnetic drift and adiabatic energy loss. Since the whole transport is strongly related to the interplanetary magnetic field (IMF) structure, a better understanding of his description is needed in order to reproduce the cosmic rays intensity at the Earth, as well as outside the ecliptic plane. In this work an interplanetary magnetic field model including the standard description on ecliptic region and a polar correction is presented. This treatment of the IMF, implemented in the HelMod Monte Carlo code (version 2.0), was used to determine the effects on the differential intensity of Proton at 1\,AU and allowed one to investigate how latitudinal gradients of proton intensities, observed in the inner heliosphere with the Ulysses spacecraft during 1995, can be affected by the modification of the IMF in the polar regions.Comment: accepted for publication inAdvances in Astronom

Proton Modulation in the Heliosphere for Different Solar Conditions and Prediction for AMS-02

Spectra of Galactic Cosmic Rays (GCRs) measured at the Earth are the combination of several processes: sources production and acceleration, propagation in the interstellar medium and propagation in the heliosphere. Inside the solar cavity the flux of GCRs is reduced due to the solar modulation, the interaction which they have with the interplanetary medium. We realized a 2D stochastic simulation of solar modulation to reproduce CR spectra at the Earth, and evaluated the importance in our results of the Local Interstellar Spectrum (LIS) model and its agreement with data at high energy. We show a good agreement between our model and the data taken by AMS-01 and BESS experiments during periods with different solar activity conditions. Furthermore we made a prediction for the flux which will be measured by AMS-02 experiment.Comment: Accepted for publication in the Proceedings of the ICATPP Conference on Cosmic Rays for Particle and Astroparticle Physics, Villa Olmo (Como, Italy), 7-8 October, 2010, to be published by World Scientific (Singapore