Observations of high-energy gamma-rays with the Fermi Observatory

The Fermi Gamma-Ray Space Telescope is a satellite-based observatory that explores the gamma-ray sky in a wide energy range from a few keV to more than 300 GeV, allowing the investigation of many fields of gamma-ray astrophysics. Fermi will open a new and important window on a wide variety of phenomena, including black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. The primary instrument is the Large Area Telescope (LAT), which measures gamma-ray flux and spectra from 20 MeV to > 300 GeV and is a successor to the highly successful EGRET experiment on CGRO. The LAT has better angular resolution, greater effective area, wider field of view and broader energy coverage than any previous experiment in this energy range. The detectors were integrated with the spacecraft in December 2006 and Fermi has been launched on June, 11 2008 from Kennedy Space Flight Centre (NASA). In an early phase of the operations, a series of calibrations and performance measurements and monitoring were performed and the first sky images were collected. This paper will present a short review of the Fermi observatory physics and the first sky images collected during the first 6 months of the science phase of the mission

Study of the Performance and Calibration of the GLAST-LAT Silicon Tracker

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A hashtag worth a thousand words: Discursive strategies around #JeNeSuisPasCharlie after the 2015 Charlie Hebdo shooting

Following a shooting attack by two self-proclaimed Islamist gunmen at the offices of French satirical weekly Charlie Hebdo on 7 January 2015, there emerged the hashtag #JeSuisCharlie on Twitter as an expression of solidarity and support for the magazine’s right to free speech. Almost simultaneously, however, there was also #JeNeSuisPasCharlie explicitly countering the former, affirmative hashtag. Based on a multimethod analysis of 74,047 tweets containing #JeNeSuisPasCharlie posted between 7 and 11 January, this article reveals that users of the hashtag under study employed various discursive strategies and tactics to challenge the mainstream framing of the shooting as the universal value of freedom of expression being threatened by religious extremism, while protecting themselves from the risk of being viewed as disrespecting victims or endorsing the violence committed. The significance of this study is twofold. First, it extends the literature on strategic speech acts by examining how such acts take place in a social media context. Second, it highlights the need for a multidimensional and reflective methodology when dealing with data mined from social media