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We discuss the ability of the GLAST Large Area Telescope (LAT) to identify, resolve, and study the high energy gamma-ray sky. Compared to previous instruments the telescope will have greatly improved sensitivity and ability to localize gamma-ray point sources. The ability to resolve the location and identity of EGRET unidentified sources is described. We summarize the current knowledge of the high energy gamma-ray sky and discuss the astrophysics of known and some prospective classes of gamma-ray emitters. In addition, we also describe the potential of GLAST to resolve old puzzles and to discover new classes of sources.
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The high-lights of ground-based very-high-energy (VHE, $E>100$ GeV) gamma-ray astronomy are reviewed. The summary covers both Galactic and extra-galactic sources. A total of at least 70 sources are currently known. Implications for our understanding of the non-thermal Universe are discussed. The next generation of ground based gamma-ray instruments aims to cover the entire accessible energy range from as low as $approx 10$ GeV up to $10^5$ GeV and to improve the sensitivity by an order of magnitude in comparison with current instruments.
I describe the different classes of Active Galactic Nuclei (AGN) and the basic tenets of unified schemes. I then review the properties of the extragalactic sources detected in the GeV and TeV bands, showing that the vast majority of them belong to the very rare blazar class. I further discuss the kind of AGN GLAST is likely to detect, making some predictions going from the obvious to the likely, all the way to the less probable.
Extraterrestrial gamma-ray astronomy is now a source of new knowledge in the fields of astrophysics, cosmic-ray physics, and the nature of dark matter. The next absolutely necessary step in the development of extraterrestrial high-energy gamma-ray astronomy is the improvement of the physical and technical characteristics of gamma-ray telescopes, especially the angular and energy resolutions. Such a new generation telescope will be GAMMA-400. GAMMA-400, currently developing gamma-ray telescope, together with X-ray telescope will precisely and detailed observe in the energy range of ~20 MeV to ~1000 GeV and 3-30 keV the Galactic plane, especially, Galactic Center, Fermi Bubbles, Crab, Cygnus, etc. The GAMMA- 400 will operate in the highly elliptic orbit continuously for a long time with the unprecedented angular (~0.01{deg} at E{gamma} = 100 GeV) and energy (~1% at E{gamma} = 100 GeV) resolutions better than the Fermi-LAT, as well as ground gamma-ray telescopes, by a factor of 5-10. GAMMA-400 will permit to resolve gamma rays from annihilation or decay of dark matter particles, identify many discrete sources (many of which are variable), to clarify the structure of extended sources, to specify the data on the diffuse emission.
Cosmic-ray (CR) sources temporarily enhance the relativistic particle density in their vicinity over the background distribution accumulated from the Galaxy-wide past injection activity and propagation. If individual sources are close enough to the solar system, their localised enhancements may present as features in the measured spectra of the CRs and in the associated secondary electromagnetic emissions. Large scale loop like structures visible in the radio sky are possible signatures of such nearby CR sources. If so, these loops may also have counterparts in the high-latitude $gamma$-ray sky. Using $sim$10 years of data from the Fermi Large Area Telescope, applying Bayesian analysis including Gaussian Processes, we search for extended enhanced emission associated with putative nearby CR sources in the energy range from 1 GeV to 1 TeV for the sky region $|b| > 30^circ$. We carefully control the systematic uncertainty due to imperfect knowledge of the interstellar gas distribution. Radio Loop~IV is identified for the first time as a $gamma$-ray emitter and we also find significant emission from Loop~I. Strong evidence is found for asymmetric features about the Galactic $l = 0^circ$ meridian that may be associated with parts of the so-called Fermi Bubbles, and some evidence is also found for $gamma$-ray emission from other radio loops. Implications for the CRs producing the features and possible locations of the sources of the emissions are discussed.
Gamma-sky.net is a novel interactive website designed for exploring the gamma-ray sky. The Map View portion of the site is powered by the Aladin Lite sky atlas, providing a scalable survey image tesselated onto a three-dimensional sphere. The map allows for interactive pan and zoom navigation as well as search queries by sky position or object name. The default image overlay shows the gamma-ray sky observed by the Fermi-LAT gamma-ray space telescope. Other survey images (e.g. Planck microwave images in low/high frequency bands, ROSAT X-ray image) are available for comparison with the gamma-ray data. Sources from major gamma-ray source catalogs of interest (Fermi-LAT 2FHL, 3FGL and a TeV source catalog) are overlaid over the sky map as markers. Clicking on a given source shows basic information in a popup, and detailed pages for every source are available via the Catalog View component of the website, including information such as source classification, spectrum and light-curve plots, and literature references. We intend for gamma-sky.net to be applicable for both professional astronomers as well as the general public. The website started in early June 2016 and is being developed as an open-source, open data project on GitHub (https://github.com/gammapy/gamma-sky). We plan to extend it to display more gamma-ray and multi-wavelength data. Feedback and contributions are very welcome!
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