107 research outputs found
Baseline Design for a Next Generation Wide-Field-of-View Very-High-Energy Gamma-Ray Observatory
The TeV gamma ray sky is observable by recording footprints of extensive air
showers with an array of particle detectors. In the northern hemisphere there
are currently two projects employing this technique: The HAWC gamma ray
observatory which is currently operational in Mexico and LHAASO in the Sichuan
region in China which is currently under development. In the southern
hemisphere several efforts are currently ongoing to investigate the feasibility
of a similar observatory at very high altitude sites in the Andes. The science
case for such an observatory should be complementary to the science to be
performed by the future Cherenkov Telescope Array. There are two clear
directions in which such an observatory could optimize its performance.
Firstly, optimize the performance of sub-TeV energies. This is especially
important to provide an unbiased monitoring of a large fraction of the sky for
observations of transient and extended sources. Secondly, to obtain the largest
photon statistics above roughly 50 TeV, which requires a large collection area
with sufficient performance in angular and energy resolution. This would enable
to extend spectral measurements of Galactic sources and gives the opportunity
to search for dark matter and exotic physics in a new energy range. Using
simulated air showers and a generalized detector description the performance of
a conceptual observatory is studied and the ways to optimize it will be
discussed. With this approach the baseline design of such an observatory can be
obtained without the need of detailed simulations of the detector hardware.Comment: Proceeding if the 35th International Cosmic Ray Conferenc
Characteristics of extensive air showers around the energy threshold for ground-particle-based gamma-ray observatories
Very high energy gamma-ray astronomy based on the measurement of air shower
particles at ground-level has only recently been established as a viable
approach, complementing the well established air Cherenkov technique. This
approach requires high (mountain) altitudes and very high surface coverage
particle detectors. While in general the properties of air showers are well
established for many decades, the extreme situation of ground-level detection
of very small showers from low energy primaries has not yet been well
characterised for the purposes of gamma-ray astronomy. Here we attempt such a
characterisation, with the aim of supporting the optimisation of
next-generation gamma-ray observatories based on this technique. We address all
of the key ground level observables and provide parameterisations for use in
detector optimisation for shower energies around 1 TeV. We emphasise two
primary aspects: the need for large area detectors to effectively measure
low-energy showers, and the importance of muon identification for the purpose
of background rejection.Comment: This is a pre-print of an article published in EPJC. The final
authenticated version is available online at:
https://doi.org/10.1140/epjc/s10052-019-6942-
The H.E.S.S. View of the Central 200 Parsecs
The inner few hundred parsecs of our galaxy provide a laboratory for the
study of the production and propagation of energetic particles.
Very-high-energy gamma-rays provide an effective probe of these processes and,
especially when combined with data from other wave-bands, gamma-rays
observations are a powerful diagnostic tool. Within this central region, data
from the H.E.S.S. instrument have revealed three discrete sources of
very-high-energy gamma-rays and diffuse emission correlated with the
distribution of molecular material. Here I provide an overview of these recent
results from H.E.S.S.Comment: Proceedings of the Galactic Centre Workshop 200
The CTA Sensitivity to Lorentz-Violating Effects on the Gamma-Ray Horizon
The arrival of TeV-energy photons from distant galaxies is expected to be
affected by their QED interaction with intergalactic radiation fields through
electron-positron pair production. In theories where high-energy photons
violate Lorentz symmetry, the kinematics of the process is altered and the cross-section suppressed.
Consequently, one would expect more of the highest-energy photons to arrive if
QED is modified by Lorentz violation than if it is not. We estimate the
sensitivity of Cherenkov Telescope Array (CTA) to changes in the -ray
horizon of the Universe due to Lorentz violation, and find that it should be
competitive with other leading constraints.Comment: 13 pages, 4 figures, typos corrected + references added, results
unchanged. Matches version accepted by JCA
Suzaku observation of the unidentified VHE gamma-ray source HESS J1702-420
A deep X-ray observation of the unidentified very high energy (VHE) gamma-ray
source HESS J1702-420, for the first time, was carried out by Suzaku. No bright
sources were detected in the XIS field of view (FOV) except for two faint
point-like sources. The two sources, however, are considered not to be related
to HESS J1702-420, because their fluxes in the 2-10 keV band (~ 10^-14 erg s^-1
cm^-2) are ~ 3 orders of magnitude smaller than the VHE gamma-ray flux in the
1-10 TeV band (F_{TeV} = 3.1 x 10^-11 erg s^-1 cm^-2). We compared the energy
spectrum of diffuse emission, extracted from the entire XIS FOV with those from
nearby observations. If we consider the systematic error of background
subtraction, no significant diffuse emission was detected with an upper limit
of F_X <2.7 x 10^-12 erg s^-1 cm^-2 in the 2-10 keV band for an assumed
power-law spectrum of \Gamma=2.1 and a source size same as that in the VHE
band. The upper limit of the X-ray flux is twelve times as small as the VHE
gamma-ray flux. The large flux ratio (F_{TeV}/F_X) indicates that HESS
J1702-420 is another example of a "dark" particle accelerator. If we use a
simple one-zone leptonic model, in which VHE gamma-rays are produced through
inverse Compton scattering of the cosmic microwave background and interstellar
far-infrared emission, and the X-rays via the synchrotron mechanism, an upper
limit of the magnetic field (1.7 \mu G) is obtained from the flux ratio.
Because the magnetic field is weaker than the typical value in the Galactic
plane (3-10 \mu G), the simple one-zone model may not work for HESS J1702-420
and a significant fraction of the VHE gamma-rays may originate from protons.Comment: 7 pages, accepted for publication in PASJ (Suzaku and MAXI special
issue
Potential Neutrino Signals from Galactic Gamma-Ray Sources
The recent progress made in Galactic gamma-ray astronomy using the High
Energy Stereoskopic System (H.E.S.S.) instrument provides for the first time a
population of Galactic TeV gamma-rays, and hence potential neutrino sources,
for which the neutrino flux can be estimated. Using the energy spectra and
source morphologies measured by H.E.S.S., together with new parameterisations
of pion production and decay in hadronic interactions, we estimate the signal
and background rates expected for these sources in a first-generation water
Cherenkov detector (ANTARES) and a next-generation neutrino telescope in the
Mediterranean Sea, KM3NeT, with an instrumented volume of 1 km^3. We find that
the brightest gamma-ray sources produce neutrino rates above 1 TeV, comparable
to the background from atmospheric neutrinos. The expected event rates of the
brightest sources in the ANTARES detector make a detection unlikely. However,
for a 1 km^3 KM3NeT detector, event rates of a few neutrinos per year from
these sources are expected, and the detection of individual sources seems
possible. Although generally these estimates should be taken as flux upper
limits, we discuss the conditions and type of gamma-ray sources for which the
neutrino flux predictions can be considered robust.Comment: 20 pages, 4 figures; v2: ERROR in energy scale of KM3NeT effective
neutrino area corrected which resulted in event rates being about a factor 3
too low; v3: grammatical changes and update of references after receiving
proof
Editor\u27s Introduction and Acknowledgments
The article offers information related to papers that were published in the publication Research in Outdoor Education Volume 9, as well as acknowledging the efforts of all who contributed to the publication
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