98 research outputs found
Blue light in the desert night
No full textInternational audienceThe HESS array in Namibia waits for a split-second flash of blue light — Cherenkov radiation — that signals an atmospheric shower of charged particles caused by cosmic rays, explains Director Mathieu de Naurois
Extended VHE gamma-ray emission towards SGR1806-20 and stellar cluster C1 1806-20
No full textWe report the discovery, with the H.E.S.S. telescopes, of steady and extended VHE γ-ray emission towards the magnetar candidate SGR 1806-20 and parent stellar cluster C1 1806-20. Preliminary analysis suggests the VHE γ-ray flux of this source, designated HESS J1808-204 is a few×10-13 ph cm-2 s-1 TeV-1 at 1 TeV with a power-law photon spectral index Γ=2.4±0.2. The instrinsic extension and orientation matches that of the synchrotron radio nebula G10.0-0.3 which may be powered by the luminous blue variable star LBV 1806-20, a prominent member of the C1 1806-20 cluster. From the energetics of the combined VHE, X-ray, and nearby Fermi-LAT GeV emission, magnetar magnetic energy may be a dominant source of energy over spin-down power, should SGR 1806-20 power the source. Alternatively, C1 1806-20 and/or LBV 1806-20 by itself, via stellar winds, could supply sufficient energy. © 2012 American Institute of Physics.Gavin Rowell, Mathieu De Naurois, Arache Djannati Ataï, Yves Gallant, and H.E.S.S. Collaboratio
H.E.S.S.-II - Gamma ray astronomy from 20 GeV to hundreds of TeV’s
No full textSince the commissioning of the fifth, largest telescope (28 m diameter) in December 2012, H.E.S.S. II is the only hybrid array of Imaging Atmospheric Cherenkov Telescopes operating in the energy range ~ 20 GeV to ~ 100 TeV. The last years have seen a tremendous effort in the design, implementation and optimization of analysis techniques suitable for monoscopic & stereoscopic events. At the same time, a complete redesign of the acquisition scheme resulted in a very significant speed-up of repointing, allowing the big telescope to be on target just ~ 20 s after receiving a Gamma-Ray Burst (GRB) alert notification. With its deep sensitivity, broad energy range, and fast reaction time, H.E.S.S. II provides an unprecedented high-quality view of the Universe at the highest energies, in a multi-wavelength and multi-messenger approach which is currently based on agreements many collaborations including in particular Fermi, IceCube, ANTARES and VIRGO/LIGO.
In the last years, we conducted deep observations of several galactic regions of primordial importance, among them are the Galactic Center region and its halo (particularly relevant for dark matter searches), the Crab Nebula, the supernova remnant RXJ 1713.7-3946, the Vela pulsar and several binary systems such as LS 5039 and PSR B1259-63. Outside the Milky Way, the blazars PKS 2155-304 and PG 1553+113 have been extensively monitored, and H.E.S.S.-II forms part of a multi-wavelength campaign of the flaring activity of Mrk 501 in 2014.
Highlights of these observations with H.E.S.S.-II have been presented and discussed at the conference. Moreover, after ten years of H.E.S.S. phase I observations, we are currently preparing a Legacy Release of the H.E.S.S. Galactic Plane Survey. A special edition of Astronomy & Astrophysics is currently under preparation, and will contain many important legacy results from H.E.S.S.-I. Major results from this very deep scan of the MilkyWay performed with H.E.S.S.-I, including among others spectacular findings from the Large Magellanic Cloud, have been presented
Highlights from H.E.S.S.
No full textIn the 15 years since its construction, the H.E.S.S. gamma-ray observatory has allowed the study of the Very High Energy gamma-ray sky at resolutions and sensitivities which were never before possible. During this period H.E.S.S. has discovered a rich zoo of both galactic and extra galactic source classes, made measurements of the galactic cosmic ray spectrum and placed limits on fundamental physical processes. A summary of the latest H.E.S.S. results for these source classes has been presented at the conference, describing the most interesting new observations and their physical interpretation. Additionally the latest upgrades and improvements to the H.E.S.S. hardware and data analyses, and the future science prospects for the experiment have been described
L'astronomie gamma de très haute énergie de H.E.S.S. à CTA. Ouverture d'une nouvelle fenêtre astronomique sur l'Univers non thermique.
No full textThe last ten years saw the emergence of Imaging Atmospheric Cherenkov Telescopes as a mature and efficient technique for the study of the Very High Energy Universe, leading to the successful opening, mainly by the HESS experiment, of our understanding of the non-thermal Universe. This habilitation thesis summaries ten years of research in Very High Energy gamma-ray astronomy with HESS and CTA. In the first part, instrumental aspects such as the experiment conception, its calibration, the reconstruction of the events and the data analysis are presented. The second parts draws a panorama of the main discoveries in the domain.Les dix dernières années ont été marquées par l'arrivée à maturité de la technique d'imagerie Cherenkov atmosphérique, ce qui a permis, notamment grâce au réseau de télescopes HESS, l'ouverture d'une nouvelle fenêtre sur l'Univers non thermique. Ce mémoire d'habilitation retrace dix années de recherche en Astronomie Gamma de Très Haute énergie avec HESS puis CTA. Les aspects techniques tels que la conception de l'instrument, son calibrage, la reconstruction des événements et l'analyse de données sont présentées dans une première partie, tandis que la seconde brosse un panorama des grandes découvertes dans ce domaine
L'expérience CELESTE: Reconversion d'une centrale solaire pour l'astronomie gamma. Première observation de la Nébuleuse du Crabe et du Blazar Markarian~421 entre 30 et 300 GeV.
No full textMichel BAUBILLIER: Président Hélène SOL: Rapporteur François LE DIBERDER: Rapporteur David SMITH Patrick FLEURY Marie Claude COUSINOU René ONGThe CELESTE experiment is the name given to the Thémis solar plant after its transformation into a large telescope for very high energy astronomy. This project was initiated by Eric Paré, who was also the Director of this thesis up to his accidental death in July 1998. The thesis describes the work for the installation and running-in of the complex optical detection device located in place of the former furnace, at the top of the tower of the solar plant. This system allows the detection during moonless nights of atmospheric showers produced by gamma rays impinging upon the earth from the cosmos. The thesis concludes with the first observations ever done of gamma rays of about 50 GeV produced by two different cosmic sources, a Galactic object, the Crab nebula, on the one hand, and an extra-galactic super-massive black hole, Markarian~421, on the other hand.Le dispositif CELESTE désigne la transformation de la centrale solaire de Thémis (Pyrénées orientales) en un vaste télescope pour l'astronomie des très hautes énergies; le nom avait été proposé par Eric Paré, inventeur du projet, et directeur de cette thèse jusqu'à son décès accidentel en Juillet 1998. La thèse décrit le long travail de mise en place et de démarrage du projet basé sur un vaste dispositif optique placé en haut de la tour solaire pour détecter la lumière réfléchie par les héliostats. On observe ainsi, par nuits sans lune, les gerbes atmosphériques produites par les rayons gamma en provenance du cosmos. La thèse se conclut par les premières observations jamais faites de rayons gamma aux énergies d'environ 50 GeV provenant d'une part d'une source Galactique, la nébuleuse du Crabe, et d'autre part d'une source extra-galactique, un trou noir supermassif, Markarian~421
L'expérience CELESTE: Reconversion d'une centrale solaire pour l'astronomie gamma. Première observation de la Nébuleuse du Crabe et du Blazar Markarian~421 entre 30 et 300 GeV.
No full textMichel BAUBILLIER: Président Hélène SOL: Rapporteur François LE DIBERDER: Rapporteur David SMITH Patrick FLEURY Marie Claude COUSINOU René ONGThe CELESTE experiment is the name given to the Thémis solar plant after its transformation into a large telescope for very high energy astronomy. This project was initiated by Eric Paré, who was also the Director of this thesis up to his accidental death in July 1998. The thesis describes the work for the installation and running-in of the complex optical detection device located in place of the former furnace, at the top of the tower of the solar plant. This system allows the detection during moonless nights of atmospheric showers produced by gamma rays impinging upon the earth from the cosmos. The thesis concludes with the first observations ever done of gamma rays of about 50 GeV produced by two different cosmic sources, a Galactic object, the Crab nebula, on the one hand, and an extra-galactic super-massive black hole, Markarian~421, on the other hand.Le dispositif CELESTE désigne la transformation de la centrale solaire de Thémis (Pyrénées orientales) en un vaste télescope pour l'astronomie des très hautes énergies; le nom avait été proposé par Eric Paré, inventeur du projet, et directeur de cette thèse jusqu'à son décès accidentel en Juillet 1998. La thèse décrit le long travail de mise en place et de démarrage du projet basé sur un vaste dispositif optique placé en haut de la tour solaire pour détecter la lumière réfléchie par les héliostats. On observe ainsi, par nuits sans lune, les gerbes atmosphériques produites par les rayons gamma en provenance du cosmos. La thèse se conclut par les premières observations jamais faites de rayons gamma aux énergies d'environ 50 GeV provenant d'une part d'une source Galactique, la nébuleuse du Crabe, et d'autre part d'une source extra-galactique, un trou noir supermassif, Markarian~421
The Very High Energy Sky from ~ 20 GeV to Hundreds of TeV - Selected Highlights
No full textInternational audienceAfter 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
The Making of Catalogues of Very-High-Energy -ray Sources
No full textInternational audienceThirty years after the discovery of the first very-high-energy γ-ray source by the Whipple telescope, the field experienced a revolution mainly driven by the third generation of imaging atmospheric Cherenkov telescopes (IACTs). The combined use of large mirrors and the invention of the imaging technique at the Whipple telescope, stereoscopic observations, developed by the HEGRA array and the fine-grained camera, pioneered by the CAT telescope, led to a jump by a factor of more than ten in sensitivity. The advent of advanced analysis techniques led to a vast improvement in background rejection, as well as in angular and energy resolutions. Recent instruments already have to deal with a very large amount of data (petabytes), containing a large number of sources often very extended (at least within the Galactic plane) and overlapping each other, and the situation will become even more dramatic with future instruments. The first large catalogues of sources have emerged during the last decade, which required numerous, dedicated observations and developments, but also made the first population studies possible. This paper is an attempt to summarize the evolution of the field towards the building up of the source catalogues, to describe the first population studies already made possible, and to give some perspectives in the context of the upcoming, new generation of instruments
H.E.S.S. Observations of LS 5039
No full text6 pages, 9 figuresRecent observations of the binary system LS5039 with the High Energy Stereoscopic System (H.E.S.S.) revealed that its Very High Energy (VHE) gamma-ray emission is modulated at the 3.9 days orbital period of the system. The bulk of the emission is largely confined to half of the orbit, peaking around the inferior conjunction epoch of the compact object. The flux modulation provides the first indication of gamma-ray absorption by pair production on the intense stellar photon field. This implies that the production region size must be not significantly greater than the gamma-gamma photosphere size (~1 AU), thus excluding the large scale collimated outflows or jets (extending out to ~1000 AU). A hardening of the spectrum is also observed at the same epoch between 0.2 and a few TeV which is unexpected under a pure absorption scenario and could rather arise from variation with phase in the maximum electron energy and/or the dominant VHE gamma-ray production mechanism. This first-time observation of modulated gamma-ray emission allows precise tests of the acceleration and emission models in binary systems
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