408 research outputs found
Detection of very-high-energy gamma-ray emission from the vicinity of PSR B1706-44 with H.E.S.S
The energetic pulsar PSR B1706-44 and the adjacent supernova remnant (SNR)
candidate G 343.1-2.3 were observed by H.E.S.S. during a dedicated
observational campaign in 2007. A new source of very-high-energy (VHE; E > 100
GeV) gamma-ray emission, HESS J1708-443, was discovered with its centroid at
RA(J2000) = 17h08m10s and Dec(J2000) = -44d21', with a statistical error of 3
arcmin on each axis. The VHE gamma-ray source is significantly more extended
than the H.E.S.S. point-spread function, with an intrinsic Gaussian width of
0.29 +/- 0.04 deg. Its energy spectrum can be described by a power law with a
photon index Gamma = 2.0 +/- 0.1 (stat) +/- 0.2 (sys). The integral flux
measured between 1-10 TeV is ~17% of the Crab Nebula flux in the same energy
range. The possible associations with PSR B1706-44 and SNR G343.1-2.3 are
discussed.Comment: 4+ pages, 2 figures; v1 submitted to ICRC Proceedings on 15 May 2009;
v2 has additional references and minor change
Design of light concentrators for Cherenkov telescope observatories
The Cherenkov Telescope Array (CTA) will be the largest cosmic gamma ray
detector ever built in the world. It will be installed at two different sites
in the North and South hemispheres and should be operational for about 30
years. In order to cover the desired energy range, the CTA is composed of
typically 50-100 collecting telescopes of various sizes (from 6 to 24-m
diameters). Most of them are equipped with a focal plane camera consisting of
1500 to 2000 Photomultipliers (PM) equipped with light concentrating optics,
whose double function is to maximize the amount of Cherenkov light detected by
the photo-sensors, and to block any stray light originating from the
terrestrial environment. Two different optical solutions have been designed,
respectively based on a Compound Parabolic Concentrator (CPC), and on a purely
dioptric concentrating lens. In this communication are described the technical
specifications, optical designs and performance of the different solutions
envisioned for all these light concentrators. The current status of their
prototyping activities is also given
Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) will be an instrument covering a wide
energy range in very-high-energy (VHE) gamma rays. CTA will include several
types of telescopes, in order to optimize the performance over the whole energy
range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets
(including many different possible CTA layouts as sub-sets) and smaller-scale
simulations dedicated to individual aspects were carried out and are on-going.
We summarize results of the prior round of large-scale simulations, show where
the design has now evolved beyond the conservative assumptions of the prior
round and present first results from the on-going new round of MC simulations.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic
Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at
arXiv:1307.223
The camera of the fifth H.E.S.S. telescope. Part I: System description
In July 2012, as the four ground-based gamma-ray telescopes of the H.E.S.S.
(High Energy Stereoscopic System) array reached their tenth year of operation
in Khomas Highlands, Namibia, a fifth telescope took its first data as part of
the system. This new Cherenkov detector, comprising a 614.5 m^2 reflector with
a highly pixelized camera in its focal plane, improves the sensitivity of the
current array by a factor two and extends its energy domain down to a few tens
of GeV.
The present part I of the paper gives a detailed description of the fifth
H.E.S.S. telescope's camera, presenting the details of both the hardware and
the software, emphasizing the main improvements as compared to previous
H.E.S.S. camera technology.Comment: 16 pages, 13 figures, accepted for publication in NIM
First detection of a VHE gamma-ray spectral maximum from a Cosmic source: H.E.S.S. discovery of the Vela X nebula
The Vela supernova remnant (SNR) is a complex region containing a number of
sources of non-thermal radiation. The inner section of this SNR, within 2
degrees of the pulsar PSR B0833-45, has been observed by the H.E.S.S. gamma-ray
atmospheric Cherenkov detector in 2004 and 2005. A strong signal is seen from
an extended region to the south of the pulsar, within an integration region of
radius 0.8 deg. around the position (RA = 08h 35m 00s, dec = -45 deg. 36'
J2000.0). The excess coincides with a region of hard X-ray emission seen by the
ROSAT and ASCA satellites. The observed energy spectrum of the source between
550 GeV and 65 TeV is well fit by a power law function with photon index = 1.45
+/- 0.09(stat) +/- 0.2(sys) and an exponential cutoff at an energy of 13.8 +/-
2.3(stat) +/- 4.1(sys) TeV. The integral flux above 1 TeV is (1.28 +/- 0.17
(stat) +/- 0.38(sys)) x 10^{-11} cm^{-2} s^{-1}. This result is the first clear
measurement of a peak in the spectral energy distribution from a VHE gamma-ray
source, likely related to inverse Compton emission. A fit of an Inverse Compton
model to the H.E.S.S. spectral energy distribution gives a total energy in
non-thermal electrons of ~2 x 10^{45} erg between 5 TeV and 100 TeV, assuming a
distance of 290 parsec to the pulsar. The best fit electron power law index is
2.0, with a spectral break at 67 TeV.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics letter
Very high energy gamma rays from the direction of Sagittarius A*.
We report the detection of a point-like source of very high energy (VHE) -rays coincident within 1' of Sgr A *, obtained with the HESS array of Cherenkov telescopes. The -rays exhibit a power-law energy spectrum with a spectral index of and a flux above the 165 GeV threshold of m -2 s -1. The measured flux and spectrum differ substantially from recent results reported in particular by the CANGAROO collaboration
Observations of Mkn 421 in 2004 with H.E.S.S. at large zenith angles
Mkn 421 was observed during a high flux state for nine nights in April and
May 2004 with the fully operational High Energy Stereoscopic System (H.E.S.S.)
in Namibia. The observations were carried out at zenith angles of
60--65, which result in an average energy threshold of 1.5 TeV
and a collection area reaching 2~km at 10~TeV. Roughly 7000 photons from
Mkn~421 were accumulated with an average gamma-ray rate of 8 photons/min. The
overall significance of the detection exceeds 100 standard deviations. The
light-curve of integrated fluxes above 2~TeV shows changes of the diurnal flux
up to a factor of 4.3. For nights of high flux, intra-night variability is
detected with a decay time of less than 1 hour. The time averaged energy
spectrum is curved and is well described by a power-law with a photon index
\egamm and an exponential cutoff at \ecut~TeV and an average integral flux
above 2~TeV of 3 Crab flux units. Significant variations of the spectral shape
are detected with a spectral hardening as the flux increases. Contemporaneous
multi-wavelength observations at lower energies (X-rays and gamma-rays above
~GeV) indicate smaller relative variability amplitudes than seen
above 2~TeV during high flux state observed in April 2004.Comment: 5 pages, 4 figures, published in A&
H.E.S.S. observations of gamma-ray bursts in 2003-2007
Very-high-energy (VHE; >~100 GeV) gamma-rays are expected from gamma-ray
bursts (GRBs) in some scenarios. Exploring this photon energy regime is
necessary for understanding the energetics and properties of GRBs. GRBs have
been one of the prime targets for the H.E.S.S. experiment, which makes use of
four Imaging Atmospheric Cherenkov Telescopes (IACTs) to detect VHE gamma-rays.
Dedicated observations of 32 GRB positions were made in the years 2003-2007 and
a search for VHE gamma-ray counterparts of these GRBs was made. Depending on
the visibility and observing conditions, the observations mostly start minutes
to hours after the burst and typically last two hours. Results from
observations of 22 GRB positions are presented and evidence of a VHE signal was
found neither in observations of any individual GRBs, nor from stacking data
from subsets of GRBs with higher expected VHE flux according to a
model-independent ranking scheme. Upper limits for the VHE gamma-ray flux from
the GRB positions were derived. For those GRBs with measured redshifts,
differential upper limits at the energy threshold after correcting for
absorption due to extra-galactic background light are also presented.Comment: 9 pages, 4 tables, 3 figure
A possible association of the new VHE gamma-ray source HESS J1825--137 with the pulsar wind nebula G18.0--0.7
We report on a possible association of the recently discovered very
high-energy -ray source HESS J1825--137 with the pulsar wind nebula
(commonly referred to as G 18.0--0.7) of the year old
Vela-like pulsar PSR B1823--13. HESS J1825--137 was detected with a
significance of 8.1 in the Galactic Plane survey conducted with the
H.E.S.S. instrument in 2004. The centroid position of HESS J1825--137 is offset
by 11\arcmin south of the pulsar position. \emph{XMM-Newton} observations have
revealed X-ray synchrotron emission of an asymmetric pulsar wind nebula
extending to the south of the pulsar. We argue that the observed morphology and
TeV spectral index suggest that HESS J1825--137 and G 18.0--0.7 may be
associated: the lifetime of TeV emitting electrons is expected to be longer
compared to the {\it XMM-Newton} X-ray emitting electrons, resulting in
electrons from earlier epochs (when the spin-down power was larger)
contributing to the present TeV flux. These electrons are expected to be
synchrotron cooled, which explains the observed photon index of , and
the longer lifetime of TeV emitting electrons naturally explains why the TeV
nebula is larger than the X-ray size. Finally, supernova remnant expansion into
an inhomogeneous medium is expected to create reverse shocks interacting at
different times with the pulsar wind nebula, resulting in the offset X-ray and
TeV -ray morphology.Comment: 5 pages, 3 figures, to appear in Astronomy and Astrophysics Letter
Discovery of VHE gamma-rays from the high-frequency-peaked BL Lac object RGB J0152+017
Aims: The BL Lac object RGB J0152+017 (z=0.080) was predicted to be a very
high-energy (VHE; > 100 GeV) gamma-ray source, due to its high X-ray and radio
fluxes. Our aim is to understand the radiative processes by investigating the
observed emission and its production mechanism using the High Energy
Stereoscopic System (H.E.S.S.) experiment. Methods: We report recent
observations of the BL Lac source RGB J0152+017 made in late October and
November 2007 with the H.E.S.S. array consisting of four imaging atmospheric
Cherenkov telescopes. Contemporaneous observations were made in X-rays by the
Swift and RXTE satellites, in the optical band with the ATOM telescope, and in
the radio band with the Nancay Radio Telescope. Results: A signal of 173
gamma-ray photons corresponding to a statistical significance of 6.6 sigma was
found in the data. The energy spectrum of the source can be described by a
powerlaw with a spectral index of 2.95+/-0.36stat+/-0.20syst. The integral flux
above 300 GeV corresponds to ~2% of the flux of the Crab nebula. The source
spectral energy distribution (SED) can be described using a two-component
non-thermal synchrotron self-Compton (SSC) leptonic model, except in the
optical band, which is dominated by a thermal host galaxy component. The
parameters that are found are very close to those found in similar SSC studies
in TeV blazars. Conclusions: RGB J0152+017 is discovered as a source of VHE
gamma-rays by H.E.S.S. The location of its synchrotron peak, as derived from
the SED in Swift data, allows clearly classification it as a
high-frequency-peaked BL Lac (HBL).Comment: Accepted for publication in A&A Letters (5 pages, 4 figures
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