High Energy Gamma Rays

The Very High Energy Gamma Ray Astronomy (VHE) is a rapidly evolving branch of modern astronomy, which covers the range from about 50 GeV to several tens of TeV from the ground. In the past years, the second generation instruments firmly established a growing and varied list of sources including plerions, supernova remnants and active galactic nuclei, and started to study some fundamental questions such as the origin of cosmic rays or the emission mechanisms of the active galactic nuclei. New results now include the first VHE unidentified sources as well as more puzzling sources such as the Galactic center. The arrival of new generation instruments (HESS, CANGAROO III, VERITAS, MAGIC) already gives a impressive look at the near future. Here we attempt to summarize the current status of the field. We briefly describe the instruments and analysis techniques, and give an outlook on the sources detected sofar.Comment: Invited talk at the XXIV Physics in Collisions Conference (PIC04), Boston, USA, June 2004, 10 pages, LaTeX, 13 eps figures. PSN TUET0

The Very High Energy Sky from ~20 GeV to Hundreds of TeV - Selected Highlights

After nearly a decade of operation, the three major arrays of atmospheric Cherenkov telescopes have revolutionized our view of the Very High Energy Universe, unveiling more than 100 sources of various types. MAGIC, consisting of two 17 m diameter telescopes on the Canary island of La Palma, and VERITAS, with four 12 m telescopes installed in southern Arizona, USA, have primarily explored the extragalactic sky, where the majority of the sources are active galactic nuclei (AGN), with {\gamma}-ray emission originating in their relativistic jets. ...... Highlights of these observations with H.E.S.S., MAGIC and VERITAS have been presented and discussed at the conference.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherland

Ground-based detectors in very-high-energy gamma-ray astronomy

Following the discovery of the cosmic rays by Victor Hess in 1912, more than 70 years and numerous technological developments were needed before an unambiguous detection of the first very-high-energy gamma-ray source in 1989 was made. Since this discovery the field on very-high-energy gamma-ray astronomy experienced a true revolution: A second, then a third generation of instruments were built, observing the atmospheric cascades from the ground, either through the atmospheric Cherenkov light they comprise, or via the direct detection of the charged particles they carry. Present arrays, 100 times more sensitive than the pioneering experiments, have detected a large number of astrophysical sources of various types, thus opening a new window on the non-thermal Universe. New, even more sensitive instruments are currently being built; these will allow us to explore further this fascinating domain. In this article we describe the detection techniques, the history of the field and the prospects for the future of ground-based very-high-energy gamma-ray astronomy.Comment: 21 pages, 13 figure

Status and Current Sensitivity of the CELESTE Experiment

The CELESTE experiment uses the heliostats of an old solar farm in the French Pyrenees to detect gamma ray air showers by the atmospheric Cerenkov technique. CELESTE has been operating since November 1999 with an array of 40 heliostats fully instrumented with 1GHz flash ADCs. Significant advances have been made in the detector simulations and in the data analysis techniques. We report here on results from recent observations of the Crab nebula above an energy threshold of 50GeV. The results and simulations illustrate the current sensitivity of the experiment.Comment: 4 pages, 6 figures. To appear in the Proceedings of the Heidelberg Gamma Ray Symposiu

Blazar observations above 60 GeV: the Influence of CELESTE's Energy Scale on the Study of Flares and Spectra

The CELESTE atmospheric Cherenkov detector ran until June 2004. It has observed the blazars Mrk 421, 1ES 1426+428 and Mrk 501. We significantly improved our understanding of the atmosphere using a LIDAR, and of the optical throughput of the detector using stellar photometry. The new data analysis provides better background rejection. We present our light curve for Mrk 421 for the 2002-2004 season and a comparison with X-ray data and the 2004 observation of 1ES 1426+428. The new analysis will allow a more sensitive search for a signal from Mrk 501.Comment: 7 pages, 7 figures, proc. of the 35th COSPAR Scientific Assembly held in Paris, France, July 200

Analysis methods for Atmospheric Cerenkov Telescopes

Three different analysis techniques for Atmospheric Imaging System are presented. The classical Hillas parameters based technique is shown to be robust and efficient, but more elaborate techniques can improve the sensitivity of the analysis. A comparison of the different analysis techniques shows that they use different information for gamma-hadron separation, and that it is possible to combine their qualities

Observation of the microquasar LS 5039 with H.E.S.S.

texte intégral disponible sur http://proc.sf2a.asso.fr/2006/2006sf2a.conf..0125D.pdfInternational audienceThe High Energy Stereoscopic System (H.E.S.S) is an array of four imaging atmospheric-Cherenkov telescopes located in the Khomas Highlands of Namibia. The microquasar LS 5039 was serendipously detected by the instrument during the scan of the inner galactic plane in 2004. Deeper observation were carried out in 2005, and brought a clear evidence for TeV emission variability. This is after PSRB 1259-63 the second VHE gamma-rays variable galactic source discovered. We will present detailed studies of the source variability (flux and spectral shape) compared to other wavelengthes and shortly review the implications for the existing emission models

Coverability in a NonFunctional Extension of BVASS

We define Vector Addition with Sates and Split/Join Transitions, a new model that extends VASS and BVASS. We define a suitable notion of covering graph for the model, and prove its finiteness and effective constructibility, and prove a coverability theorem