728 research outputs found
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
VHE observations of the gamma-ray binary system LS 5039 with H.E.S.S
LS 5039 is a gamma-ray binary system observed in a broad energy range, from
radio to TeV energies. The binary system exhibits both flux and spectral
modulation as a function of its orbital period. The X-ray and very-high-energy
(VHE, E > 100 GeV) gamma-ray fluxes display a maximum/minimum at
inferior/superior conjunction, with spectra becoming respectively
harder/softer, a behaviour that is completely reversed in the high-energy
domain (HE, 0.1 < E < 100 GeV). The HE spectrum cuts off at a few GeV, with a
new hard component emerging at E > 10 GeV that is compatible with the
low-energy tail of the TeV emission. The low 10 - 100 GeV flux, however, makes
the HE and VHE components difficult to reconcile with a scenario including
emission from only a single particle population. We report on new observations
of LS 5039 conducted with the High Energy Stereoscopic System (H.E.S.S.)
telescopes from 2006 to 2015. This new data set enables for an
unprecedentedly-deep phase-folded coverage of the source at TeV energies, as
well as an extension of the VHE spectral range down to ~120 GeV, which makes LS
5039 the first gamma-ray binary system in which a spectral overlap between
satellite and ground-based gamma-ray observatories is obtained.Comment: Proceeding for ICRC 201
The H.E.S.S. central data acquisition system
The High Energy Stereoscopic System (H.E.S.S.) is a system of Imaging
Atmospheric Cherenkov Telescopes (IACTs) located in the Khomas Highland in
Namibia. It measures cosmic gamma rays of very high energies (VHE; >100 GeV)
using the Earth's atmosphere as a calorimeter. The H.E.S.S. Array entered Phase
II in September 2012 with the inauguration of a fifth telescope that is larger
and more complex than the other four. This paper will give an overview of the
current H.E.S.S. central data acquisition (DAQ) system with particular emphasis
on the upgrades made to integrate the fifth telescope into the array. At first,
the various requirements for the central DAQ are discussed then the general
design principles employed to fulfil these requirements are described. Finally,
the performance, stability and reliability of the H.E.S.S. central DAQ are
presented. One of the major accomplishments is that less than 0.8% of
observation time has been lost due to central DAQ problems since 2009.Comment: 17 pages, 8 figures, published in Astroparticle Physic
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