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Abramowski A.,University of Hamburg | Acero F.,Montpellier University | Aharonian F.,Max Planck Institute for Nuclear Physics | Aharonian F.,Dublin Institute for Advanced Studies | And 103 more authors.
Astroparticle Physics | Year: 2011

Several models of Quantum Gravity predict Lorentz Symmetry breaking at energy scales approaching the Planck scale (∼1019 GeV). With present photon data from the observations of distant astrophysical sources, it is possible to constrain the Lorentz Symmetry breaking linear term in the standard photon dispersion relations. Gamma Ray Bursts (GRB) and flaring Active Galactic Nuclei (AGN) are complementary to each other for this purpose, since they are observed at different distances in different energy ranges and with different levels of variability. Following a previous publication of the High Energy Stereoscopic System (H.E.S.S.) collaboration [1], a more sensitive event-by-event method consisting of a likelihood fit is applied to PKS 2155-304 flare data of MJD 53944 (July 28, 2006) as used in the previous publication. The previous limit on the linear term is improved by a factor of ∼3 up to MQGl>2.1×1018 GeV and is currently the best result obtained with blazars. The sensitivity to the quadratic term is lower and provides a limit of MQGq> 6.4 × 10 10 GeV, which is the best value obtained so far with an AGN and similar to the best limits obtained with GRB. © 2011 Elsevier B.V. All rights reserved.

PubMed | University of Witwatersrand, Armenian National Academy of Sciences, German Electron Synchrotron, Montpellier University and 30 more.
Type: Journal Article | Journal: Physical review letters | Year: 2014

Gamma-ray line signatures can be expected in the very-high-energy (E()>100 GeV) domain due to self-annihilation or decay of dark matter (DM) particles in space. Such a signal would be readily distinguishable from astrophysical -ray sources that in most cases produce continuous spectra that span over several orders of magnitude in energy. Using data collected with the H.E.S.S. -ray instrument, upper limits on linelike emission are obtained in the energy range between 500 GeV and 25 TeV for the central part of the Milky Way halo and for extragalactic observations, complementing recent limits obtained with the Fermi-LAT instrument at lower energies. No statistically significant signal could be found. For monochromatic -ray line emission, flux limits of (2 10(-7) -2 10(-5)) m(-2) s(-1) sr(-1) and (1 10(-8) -2 10(-6)) m(-2) s(-1)sr(-1) are obtained for the central part of the Milky Way halo and extragalactic observations, respectively. For a DM particle mass of 1 TeV, limits on the velocity-averaged DM annihilation cross section v( ) reach 10(-27)cm(3)s(-1), based on the Einasto parametrization of the Galactic DM halo density profile.

PubMed | University of Witwatersrand, Armenian National Academy of Sciences, German Electron Synchrotron, Montpellier University and 31 more.
Type: Journal Article | Journal: Physical review letters | Year: 2016

The inner region of the MilkyWay halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using -ray observations towards the inner 300pc of the MilkyWay, with the H.E.S.S. array of ground-based Cherenkov telescopes. The analysis is based on a 2D maximum likelihood method using Galactic Center (GC) data accumulated by H.E.S.S. over the last 10years (2004-2014), and does not show any significant -ray signal above background. Assuming Einasto and Navarro-Frenk-White DM density profiles at the GC, we derive upper limits on the annihilation cross section v. These constraints are the strongest obtained so far in the TeV DM mass range and improve upon previous limits by a factor 5. For the Einasto profile, the constraints reach v values of 610^{-26}cm^{3}s^{-1} in the W^{+}W^{-} channel for a DM particle mass of 1.5TeV, and 210^{-26}cm^{3}s^{-1} in the ^{+}^{-} channel for a 1TeV mass. For the first time, ground-based -ray observations have reached sufficient sensitivity to probe v values expected from the thermal relic density for TeV DM particles.

Domainko W.,Max Planck Institute for Nuclear Physics | Clapson A.-C.,Max Planck Institute for Nuclear Physics | Brun F.,Ecole Polytechnique - Palaiseau | Eger P.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 4 more authors.
Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011 | Year: 2011

Globular clusters are old stellar systems which exhibit very-high stellar densities in their cores. The globular cluster Terzan 5 is characterized by a high stellar encounter rate and hosts the largest detected population of millisecond pulsars. It also features bright GeV gamma-ray emission and extended X-ray radiation. However, no globular clusters have been detected in very-high-energy gamma rays (VHE, E> 100 GeV) so far. In order to investigate this possibility Terzan 5 has been observed with the H.E.S.S. telescope array in this energy band. The discovery of a source of VHE gamma rays from the direction of this globular cluster will be reported. The results of the VHE analysis and a multi-wavelength view of Terzan 5 will be presented in this contribution. No counterpart of model can fully explain the observed morphology of the detected VHE gamma-ray source.

Gargate L.,University of Lisbon | Gargate L.,Princeton University | Fonseca R.A.,University of Lisbon | Niemiec J.,Instytut Fizyki Jadrowej PAN | And 5 more authors.
Astrophysical Journal Letters | Year: 2010

A non-resonant instability for the amplification of the interstellar magnetic field in young supernova remnant (SNR) shocks was predicted by Bell, and is thought to be relevant for the acceleration of cosmic-ray (CR) particles. For this instability, the CRs streaming ahead of SNR shock fronts drive electromagnetic waves with wavelengths much shorter than the typical CR Larmor radius, by inducing a current parallel to the background magnetic field. We explore the nonlinear regime of the non-resonant mode using Particle-in-Cell hybrid simulations, with kinetic ions and fluid electrons, and analyze the saturation mechanism for realistic CR and background plasma parameters. In the linear regime, the observed growth rates and wavelengths match the theoretical predictions; the nonlinear stage of the instability shows a strong reaction of both the background plasma and the CR particles, with the saturation level of the magnetic field varying with the CR parameters. The simulations with CR-to-background density ratios of n CR/n b = 10 -5 reveal the highest magnetic field saturation levels, with energy also being transferred to the background plasma and to the perpendicular velocity components of the CR particles. The results show that amplification factors > 10 for the magnetic field can be achieved, and suggest that this instability is important for the generation of magnetic field turbulence, and for the acceleration of CR particles. © 2010. The American Astronomical Society. All rights reserved.

Mandowska E.,Instytut Fizyki | Mandowski A.,Instytut Fizyki | Bluszcz A.,Silesian University of Technology | Adamiec G.,Silesian University of Technology | And 4 more authors.
Przeglad Elektrotechniczny | Year: 2016

Optically stimulated luminescence (OSL) is observed in irradiated insulators or semiconductors exposed to light of the appropriate energy. OSL Intensity is normally proportional to the dose of absorbed radiation. For this reason OSL method is often used in radiation dosimetry and dating in archeology and geology. OSL characteristics might also provide information about the parameters of traps and recombination centers of the material. The most common method of optical stimulation is the stimulation by continuous light in the range from a few to several seconds. The recently developed TL/OSL reader Jupiter provides several new methods of stimulation. They allow, among others, determination of long-lived characteristics of a detector and the activation energy of traps. © 2016, Wydawnictwo SIGMA - N O T Sp. z o.o. All rights reserved.

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