1,721,294 research outputs found
Gamma Ray Astronomy above 30 GeV with the MAGIC Telescope
No full textThe MAGIC Telescope is now on its final commissioning phase and will become operational before the end of 2003. Many technical innovations contribute in lowering the energy threshold to 30 GeV. Among them, the all-aluminium parabolic reflecting surface that, with its 236 m^2 makes up the biggest present Cherenkov telescope and a smart trigger able to cope with the increased background rate. In this contribution, along with a brief overview of the scientific goals of MAGIC, details will be given on the construction and performances of the reflecting surface as well as the expected rejection capabilities of the two-level trigger
Highlights of MAGIC results
No full textMAGIC is the largest Cherenkov telescope currently operating and is in full operation since September 2004. Since then, it is providing a full wealth of exciting new physics results from its observations in the very high energy (VHE) region of galactic and extragalactic locations. Among the main results obtained, the discoveries of new sources and even of entire new classes of sources, as well as the observation of fast variability down to an unprecedented level of precision. Recent results for distant extragalactic sources are also shown: observations that are important for the development of new models of extragalactic background and to evaluate the systematic uncertainties of the imaging Cherenkov technique
Detection of a flare at Fermi LAT energies during a multiwavelength campaign on Markarian 180
No full textWe present the results of the analysis of Markarian 180 (1ES 1133+704), a BL Lac object embedded in a giant elliptical galaxy, obtained for a period of 45 day, during which multi-wavelength observations were ongoing. The multi-wavelength campaign on Mrk180 was in 2008 (from 2008-10-24 to 2008-12-08) and was coordinated by Stefan Rugamer (MAGIC Collaboration). The Mrk 180 is associated with a quasar-like object whose distance can be determined unambiguously, thanks to the measurement of absorption line that gives the redshift (z=0.046; Ulrich 1978). The source was observed by the LAT of the Fermi satellite, and it was possible to discover a change of flux, at the energies 100 MeV–300 GeV, during the multi-wavelength campaign period. Results of the analysis are shown
Sensitivity to Gamma-Ray Bursts of a Nanosatellite MeV Telescope with a Silicon Tracker
Full text linkWe propose a nanosatellite Compton telescope based on a silicon tracker, both as a fast and low-cost mission for astrophysics in the MeV regime and as a pathfinder for future large-scale Compton orbital observatories. In this paper we assess the sensitivity of such an instrument for the observation of gamma-ray bursts
Mining extra-galactic sources: lessons learnt from the analysis of the Fermi LAT data
No full textDiscovering and locating gamma-ray sources in the whole sky map is a declared target of the Fermi Gamma-ray Space Telescope collaboration. We discuss the statistical problems encountered while analysing the collection of high-energy photons accumulated by the Large Area Telescope, the principal instrument on board the Fermi spacecraft, over a period of around 7.5 years using unsupervised learning. In particular, we present a Bayesian mixture model where a fixed, though unknown, number of parametric components identify the extra-galactic emitting sources we are searching for, while a further component represents parametrically the diffuse gamma-ray background due to both, extra-galactic and galactic high-energy photon emission. We determine the number of sources, their co- ordinates on the map and their intensities. The model parameters are estimated using a reversible jump MCMC algorithm which implements four different types of moves. These allow us to explore the dimension of the parameter space. The possible transitions remove from or add a source to the model, while leaving the background component unchanged. We furthermore present an heuristic procedure, based on the posterior distribution of the mixture weights, to qualify the nature of each detected source
Discovering and locating high-energy exta-galactic sources by Bayesian mixture modelling
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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