643 research outputs found
Observations of the Crab Nebula with H.E.S.S. Phase II
The High Energy Stereoscopic System (H.E.S.S.) phase I instrument was an
array of four mirror area Imaging Atmospheric Cherenkov
Telescopes (IACTs) that has very successfully mapped the sky at photon energies
above GeV. Recently, a telescope was added to
the centre of the existing array, which can be operated either in standalone
mode or jointly with the four smaller telescopes. The large telescope lowers
the energy threshold for gamma-ray observations to several tens of GeV, making
the array sensitive at energies where the Fermi-LAT instrument runs out of
statistics. At the same time, the new telescope makes the H.E.S.S. phase II
instrument. This is the first hybrid IACT array, as it operates telescopes of
different size (and hence different trigger rates) and different field of view.
In this contribution we present results of H.E.S.S. phase II observations of
the Crab Nebula, compare them to earlier observations, and evaluate the
performance of the new instrument with Monte Carlo simulations.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
TeV neutrinos and gamma rays from pulsars
Recent studies suggest that pulsars could be strong sources of TeV muon
neutrinos provided positive ions are accelerated by pulsar polar caps to PeV
energies. In such a situation muon neutrinos are produced through the delta
resonance in interactions of pulsar accelerated ions with its thermal radiation
field. High energy gamma rays also should be produced simultaneously in pulsar
environment as both charged and neutral pions are generated in the interactions
of energetic hadrons with the ambient photon fields. Here we estimate TeV gamma
ray flux at Earth from few nearby young pulsars. When compared with the
observations we find that proper consideration of the effect of polar cap
geometry in flux calculation is important. Incorporating such an effect we
obtain the (revised) event rates at Earth due to few potential nearby pulsars.
The results suggest that pulsars are unlikely to be detected by the upcoming
neutrino telescopes. We also estimate TeV gamma ray and neutrino fluxes from
pulsar nebulae for the adopted model of particle acceleration.Comment: Six pages, accepted in MNRA
Automatic Detection and Prediction of the Transition Between the Behavioural States of a Subject Through a Wearable CPS
The PRESLEEP project is aimed at the fine assessment and validation of the proposed proprietary methodology/technology, for the automatic detection and prediction of the transition between the behavioural states of a subject (e.g. wakefulness, drowsiness and sleeping) through a wearable Cyber Physical System (CPS). The Intellectual Property (IP) is based on a combined multi-factor and multi-domain analysis thus being able to extract a robust set of parameters despite of the, generally, low quality of the physiological signals measured through a wearable system applied to the wrist of the subject. An application experiment has been carried out at AVL, based on reduced wakefulness maintenance test procedure, to validate the algorithm’s detection and prediction capability once the subject is driving in the dynamic vehicle simulator
Exploring the Galaxy at TeV energies: Latest results from the H.E.S.S. Galactic Plane Survey
The High Energy Stereoscopic System (H.E.S.S.) is an array of four imaging
atmospheric-Cherenkov telescopes located in Namibia and designed to detect
extensive air showers initiated by gamma-rays in the very-high-energy domain.
It is an ideal instrument for surveying the Galactic plane in search of new
sources, thanks to its location in the Southern Hemisphere, its excellent
sensitivity, and its large field-of-view. The efforts of the H.E.S.S. Galactic
Plane Survey, the first comprehensive survey of the inner Galaxy at TeV
energies, have contributed to the discovery of an unexpectedly large and
diverse population of over 60 sources of VHE gamma rays within its current
range of l=250 to 65 degrees in longitude and |b|<=3.5 degrees in latitude. The
population of VHE gamma-ray emitters is dominated by the pulsar wind nebula and
supernova remnant source classes, although nearly a third remain unidentified
or confused.
The sensitivity of H.E.S.S. to sources in the inner Galaxy has improved
significantly over the past two years, from continued survey observations,
dedicated follow-up observations of interesting source candidates, and from the
development of advanced methods for discrimination of gamma-ray-induced showers
from the dominant background of hadron-induced showers. The latest maps of the
Galaxy at TeV energies will be presented, and a few remarkable new sources will
be highlighted.Comment: 4 pages, 2 figures, appears in the Proceedings of the 32nd
International Cosmic Ray Conference (ICRC 2011), Beijing, China, 11th to 18th
August 201
Mrk 421, Mrk 501, and 1ES 1426+428 at 100 GeV with the CELESTE Cherenkov Telescope
We have measured the gamma-ray fluxes of the blazars Mrk 421 and Mrk 501 in
the energy range between 50 and 350 GeV (1.2 to 8.3 x 10^25 Hz). The detector,
called CELESTE, used first 40, then 53 heliostats of the former solar facility
"Themis" in the French Pyrenees to collect Cherenkov light generated in
atmospheric particle cascades. The signal from Mrk 421 is often strong. We
compare its flux with previously published multi-wavelength studies and infer
that we are straddling the high energy peak of the spectral energy
distribution. The signal from Mrk 501 in 2000 was weak (3.4 sigma). We obtain
an upper limit on the flux from 1ES 1426+428 of less than half that of the Crab
flux near 100 GeV. The data analysis and understanding of systematic biases
have improved compared to previous work, increasing the detector's sensitivity.Comment: 15 pages, 14 figures, accepted to A&A (July 2006) August 19 --
corrected error in author lis
Supersymmetric dark matter in M31: can one see neutralino annihilation with CELESTE?
It is widely believed that dark matter exists within galaxies and clusters of
galaxies. Under the assumption that this dark matter is composed of the
lightest, stable supersymmetric particle, assumed to be the neutralino, the
feasibility of its indirect detection via observations of a diffuse gamma-ray
signal due to neutralino annihilations within M31 is examined. To this end,
first the dark matter halo of the close spiral galaxy M31 is modeled from
observations, then the resultant gamma-ray flux is estimated within
supersymmetric model configurations. We conclude that under favorable
conditions such as the rapid accretion of neutralinos on the central black hole
in M31 and/or the presence of many clumps inside its halo with inner
profiles, a neutralino annihilation gamma-ray signal is marginally detectable
by the ongoing collaboration CELESTE.Comment: Latex, 32 pages, 12 figures, 5 table
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
Discovery of the Binary Pulsar PSR B1259-63 in Very-High-Energy Gamma Rays around Periastron with H.E.S.S
We report the discovery of very-high-energy (VHE) gamma-ray emission of the
binary system PSR B1259-63/SS 2883 of a radio pulsar orbiting a massive,
luminous Be star in a highly eccentric orbit. The observations around the 2004
periastron passage of the pulsar were performed with the four 13 m Cherenkov
telescopes of the H.E.S.S. experiment, recently installed in Namibia and in
full operation since December 2003. Between February and June 2004, a gamma-ray
signal from the binary system was detected with a total significance above 13
sigma. The flux was found to vary significantly on timescales of days which
makes PSR B1259-63 the first variable galactic source of VHE gamma-rays
observed so far. Strong emission signals were observed in pre- and
post-periastron phases with a flux minimum around periastron, followed by a
gradual flux decrease in the months after. The measured time-averaged energy
spectrum above a mean threshold energy of 380 GeV can be fitted by a simple
power law F_0(E/1 TeV)^-Gamma with a photon index Gamma =
2.7+-0.2_stat+-0.2_sys and flux normalisation F_0 = (1.3+-0.1_stat+-0.3_sys)
10^-12 TeV^-1 cm^-2 s^-1. This detection of VHE gamma-rays provides unambiguous
evidence for particle acceleration to multi-TeV energies in the binary system.
In combination with coeval observations of the X-ray synchrotron emission by
the RXTE and INTEGRAL instruments, and assuming the VHE gamma-ray emission to
be produced by the inverse Compton mechanism, the magnetic field strength can
be directly estimated to be of the order of 1 G.Comment: 10 pages, 8 figures, accepted in Astronomy and Astrophysics on 2 June
2005, replace: document unchanged, replaced author field in astro-ph entry -
authors are all members of the H.E.S.S. collaboration and three additional
authors (99+3, see document
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