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Search Results: 1 - 10 of 175496 matches for " Mathieu de Naurois "
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The Galactic Sky seen by H.E.S.S
Mathieu de Naurois
Physics , 2011, DOI: 10.1016/j.asr.2011.04.009
Abstract: The H.E.S.S. experiment is an array of four imaging Cherenkov telescopes located in the Khomas Highlands of Namibia. It has been operating in its full configuration since December 2003 and detects very-high-energy (VHE) gamma rays ranging from 100 GeV to 50 TeV. Since 2004, the continuous observation of the Galactic Plane by the H.E.S.S. array of telescopes has yielded the discovery of more than 50 sources, belonging to the classes of pulsar wind nebulae (PWN), supernova remnants (SNR), gamma ray binaries and, more recently, a stellar cluster and molecular clouds in the vicinity of shell-type SNRs. Galactic emission seen by H.E.S.S. and its implications for particle acceleration in our Galaxy are discussed.
A high performance likelihood reconstruction of gamma-rays for Imaging Atmospheric Cherenkov Telescopes
Mathieu de Naurois,Loic Rolland
Physics , 2009, DOI: 10.1016/j.astropartphys.2009.09.001
Abstract: We present a sophisticated gamma-ray likelihood reconstruction technique for Imaging Atmospheric Cerenkov Telescopes. The technique is based on the comparison of the raw Cherenkov camera pixel images of a photon induced atmospheric particle shower with the predictions from a semi-analytical model. The approach was initiated by the CAT experiment in the 1990's, and has been further developed by a new fit algorithm based on a log-likelihood minimisation using all pixels in the camera, a precise treatment of night sky background noise, the use of stereoscopy and the introduction of first interaction depth as parameter of the model. The reconstruction technique provides a more precise direction and energy reconstruction of the photon induced shower compared to other techniques in use, together with a better gamma efficiency, especially at low energies, as well as an improved background rejection. For data taken with the H.E.S.S. experiment, the reconstruction technique yielded a factor of ~2 better sensitivity compared to the H.E.S.S. standard reconstruction techniques based on second moments of the camera images (Hillas Parameter technique).
Exploiting the time of arrival of Cherenkov photons at the 28 m H.E.S.S. telescope for background rejection: Methods and performance
Rapha?l Chalmé-Calvet,Markus Holler,Mathieu de Naurois,Jean-Paul Tavernet,for the H. E. S. S. Collaboration
Physics , 2015,
Abstract: In 2012, the High Energy Stereoscopic System (H.E.S.S.) was expanded by a fifth telescope (CT5). With an effective mirror diameter of 28m, CT5 is able to detect the Cherenkov light of very faint gamma-ray air showers, thereby significantly lowering the energy threshold of this telescope compared to the other four telescopes. Extracting as much information as possible from the recorded shower image is crucial for background rejection and to reach an energy threshold of a few tens of GeV. The camera of CT5 is conceived to register the time of the charge pulse maximum with respect to the beginning of the 16 ns integration window of each pixel. This information can be utilised to improve the event reconstruction. It also helps to reduce the background contamination at low energies. We present new techniques for background rejection based on CT5 timing information and evaluate their performance.
Discovery of VHE gamma-ray emission from the W49 region with H.E.S.S
Francois Brun,Mathieu de Naurois,Werner Hofmann,Svenja Carrigan,Arache Djannati-Ata?,Stefan Ohm,for the H. E. S. S. Collaboration
Physics , 2011,
Abstract: The W49 region hosts two bright radio sources: the star forming region W49A and the supernova remnant W49B. The 10^6 M_odot Giant Molecular Cloud W49A is one of the most luminous giant radio HII regions in our Galaxy and hosts several active, high-mass star formation sites. The mixed-morphology supernova remnant W49B has one of the highest surface brightness in radio of all the SNRs of this class in our Galaxy and is one of the brightest ejecta-dominated SNRs in X-rays. Infrared observations evidenced that W49B is interacting with molecular clouds and Fermi recently reported the detection of a coincident bright, high-energy gamma-ray source. Observations by the H.E.S.S. telescope array resulted in the significant detection of VHE gamma-ray emission from the W49 region, compatible with VHE emission from the SNR W49B. The results, the morphology and the origin of the VHE emission are presented in the multi-wavelength context and the implications on the origin of the signal are discussed.
Observations of TeV binary systems with the H.E.S.S. telescope
Pol Bordas,Hélène Laffon,Mathieu de Naurois,Stefan Ohm,Emma de O?a Wilhelmi,Iurii Sushch,Francesca Volpe,Víctor Zabalza,for the H. E. S. S. Collaboration
Physics , 2013,
Abstract: Recent observations of binary systems obtained with the H.E.S.S. telescopes are providing crucial information on the physics of relativistic outflows and the engines powering them. We report here on new H.E.S.S. results on HESS J0632+057, PSR B1259-63/LS 2883, Eta Carinae and the recently discovered source HESS J1018-589. Despite the high-quality data obtained in the last years through both ground and space-based gamma-ray detectors, many questions on the mechanisms that permit binary systems to emit at gamma-rays remain open. In particular, it is becoming apparent that emission at high and very-high energies is uncorrelated in some gamma-ray binary systems, with bright GeV flares not observed at TeV energies (e.g. PSR B1259-63), and sources periodically detected at VHEs which are lacking its HE counterpart (e.g. HESS J0632+057). Our results mainly confirm the predictions derived previously for the studied sources, but unexpected results are also found in a few cases, which are discussed in the context of contemporaneous observations at lower energies.
The Very High Energy Sky from ~20 GeV to Hundreds of TeV - Selected Highlights
M. de Naurois
Physics , 2015,
Abstract: 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.
A Measure of Space for Computing over the Reals
Paulin Jacobé De Naurois
Computer Science , 2006,
Abstract: We propose a new complexity measure of space for the BSS model of computation. We define LOGSPACE\_W and PSPACE\_W complexity classes over the reals. We prove that LOGSPACE\_W is included in NC^2\_R and in P\_W, i.e. is small enough for being relevant. We prove that the Real Circuit Decision Problem is P\_R-complete under LOGSPACE\_W reductions, i.e. that LOGSPACE\_W is large enough for containing natural algorithms. We also prove that PSPACE\_W is included in PAR\_R.
Exploring the Galaxy at TeV energies: Latest results from the H.E.S.S. Galactic Plane Survey
Henning Gast,Fran?ois Brun,Svenja Carrigan,Ryan C. G. Chaves,Christoph Deil,Arache Djannati-Ata?,Yves Gallant,Vincent Marandon,Mathieu de Naurois,Raquel de los Reyes,for the H. E. S. S. Collaboration
Physics , 2012,
Abstract: The High Energy Stereoscopic System (H.E.S.S.) is an array of four imaging atmospheric-Cherenkov telescopes located in Namibia and designed to detect extensive air showers initiated by gamma-rays in the very-high-energy domain. It is an ideal instrument for surveying the Galactic plane in search of new sources, thanks to its location in the Southern Hemisphere, its excellent sensitivity, and its large field-of-view. The efforts of the H.E.S.S. Galactic Plane Survey, the first comprehensive survey of the inner Galaxy at TeV energies, have contributed to the discovery of an unexpectedly large and diverse population of over 60 sources of VHE gamma rays within its current range of l=250 to 65 degrees in longitude and |b|<=3.5 degrees in latitude. The population of VHE gamma-ray emitters is dominated by the pulsar wind nebula and supernova remnant source classes, although nearly a third remain unidentified or confused. The sensitivity of H.E.S.S. to sources in the inner Galaxy has improved significantly over the past two years, from continued survey observations, dedicated follow-up observations of interesting source candidates, and from the development of advanced methods for discrimination of gamma-ray-induced showers from the dominant background of hadron-induced showers. The latest maps of the Galaxy at TeV energies will be presented, and a few remarkable new sources will be highlighted.
Status and Current Sensitivity of the CELESTE Experiment
M. de Naurois,CELESTE collaboration
Physics , 2000, DOI: 10.1063/1.1370819
Abstract: 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.
Ground-based detectors in very-high-energy gamma-ray astronomy
M. de Naurois,D. Mazin
Physics , 2015, DOI: 10.1016/j.crhy.2015.08.011
Abstract: 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.
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