674 research outputs found
Observation of Pulsed γ-Rays Above 25 GeV from the Crab Pulsar with MAGIC
No full textOne fundamental question about pulsars concerns the mechanism of their pulsed electromagnetic emission. Measuring the high-end region of a pulsar's spectrum would shed light on this question. By developing a new electronic trigger, we lowered the threshold of the Major Atmospheric γ-ray Imaging Cherenkov (MAGIC) telescope to 25 giga-electron volts. In this configuration, we detected pulsed γ-rays from the Crab pulsar that were greater than 25 giga-electron volts, revealing a relatively high cutoff energy in the phase-averaged spectrum. This indicates that the emission occurs far out in the magnetosphere, hence excluding the polar-cap scenario as a possible explanation of our measurement. The high cutoff energy also challenges the slot-gap scenario
Observation of the microquasar LS 5039 with H.E.S.S.
No full textRadio and X-ray observations have led to the presumption that some X-ray binaries (XRB) called microquasars behave as scaled down active galactic nuclei. Several models predict detectable emission of such objects by atmospheric Cherenkov telescopes above 100 GeV. LS 5039 is one of the two microquasars possibly associated with an EGRET source, and it exhibits strong radio and X-rays emission presumably associated with a relativistic jet, making it the most promising candidate for GeV-TeV emission. LS 5039 is located in the Southern Hemisphere in a region that was scanned in the summer of 2004 by the High Energy Stereoscopic System. Dedicated follow-up observations are planned for the summer of 2005. Results of these two observation campaigns are presented
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
H.E.S.S. observations of galaxy clusters
No full textClusters of galaxies, the largest gravitationally bound objects in the universe, are expected to contain a significant population of hadronic and leptonic cosmic rays. Potential sources for these particles are merger and accretion shocks, starburst driven galactic winds and radio galaxies. Furthermore, since galaxy clusters confine cosmic ray protons up to energies of at least 1 PeV for a time longer than the Hubble time they act as storehouses and accumulate all the hadronic particles which are accelerated within them. Consequently clusters of galaxies are potential sources of VHE (> 100 GeV) gamma rays. Motivated by these considerations, promising galaxy clusters are observed with the H.E.S.S. experiment as part of an ongoing campaign. Here, upper limits for the VHE gamma ray emission for the Abell 496 and Coma cluster systems are reported.W. Domainko, W. Benbow, J. A. Hinton, O. Martineau-Huynh, M. de Naurois, D. Nedbal, G. Pedaletti, G. Rowell for the 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
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
Combinaison monolithique de lasers à cascade quantique par couplage évanescent
No full textAu cours des dix dernières années, les performances des lasers à cascade quantique dans le moyen infrarouge ont connu une progression rapide: Les rendements ont atteint des valeurs supérieures à 20% avec une puissance d émission de 5W en régime continu, à température ambiante. Ces valeurs ont été atteintes notamment grâce à la diminution de la sensibilité des lasers à l échauffement, avec des températures caractéristiques T0 s approchant de 300K. Les performances sont donc actuellement limitées par la puissance injectée, qui est proportionnelle à la taille de la zone de gain. Les travaux de cette thèse présentent une solution innovante, consistant à combiner un réseau d émetteurs de petites tailles de façon monolithique. Nous démontrons expérimentalement pour la première fois, des dispositifs jusqu à 32 émetteurs de 2 m de larges, émettant en phase par couplage évanescent. De plus, nous mettons en évidences des résistances thermiques record. Ces résultats mettent en évidence la possibilité de fabriquer des sources de hautes puissances (supérieures à 10W) dans le moyen-infrarouge avec une très bonne qualité de faisceau.During the last 10 years, the quantum cascade lasers performances in the mid-infrared have been considerably improved: the wall plug efficiency has reached values superior to 20%, with output power up to 5W in continuous wave operation, at room temperature. Those values have been achieved due to the reduction of the temperature sensibility of the lasers, with characteristic temperature T0 reaching 300K. The output power is now limited to the injected power, which is proportional to the gain region size. This thesis reports an innovating solution consisting on beam combining an array of narrow emitters, monolithically. We experimentally demonstrate for the first time devices of up to 32 emitters of 2 m width emitting in phase by evanescent coupling. Moreover, we show record thermal resistance. Those results highlight the possibility to fabricate high power sources (superior to 10 W) in the mid-infrared, with a good beam quality.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF
Observation of the microquasar LS 5039 with H.E.S.S.
No full texttexte 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
A high performance likelihood reconstruction of gamma-rays for Imaging Atmospheric Cherenkov Telescopes
No full text43 pages, 33 figures, accepted for publication in Astroparticle PhysicsWe 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)
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