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Constraints on the origin of cosmic rays above 10¹⁸ eV from large-scale anisotropy searches in data of the Pierre Auger Observatory

2013-05-10T04:32:57Z

Title: Constraints on the origin of cosmic rays above 10¹⁸ eV from large-scale anisotropy searches in data of the Pierre Auger Observatory Author: Pierre Auger Collaboration; Abreu, P.;...; Barber, Kerridwen Bette; Barbosa, A. F.;...; Bellido Caceres, Jose Alfredo;; BenZvi, S.;...; Clay, Roger William;; Cocciolo, G.;...; Cooper, Mathew John; Coppens, J.;...; Dawson, Bruce Robert; de Almeida, R. M.;...; Harrison, Thomas Alan; Harton, J. L.;...; Herve, Alexander Edward; Hill, Gary Colin; Hojvat, C.;...; Holmes, Vanessa Catherine; Homola, P.;...; Sorokin, Jennifer Sally; Spinka, H.;...; Wahrlich, Philip Shane; Wainberg, O.;...; Whelan, Benjamin James; ... et al. Abstract: A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above 10¹⁸ eV at the Pierre Auger Observatory is reported. For the first time, these large-scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above 10¹⁸ eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.

Search for gravitational waves from binary black hole inspiral, merger, and ringdown in LIGO-Virgo data from 2009-2010

2013-05-10T05:09:40Z

Title: Search for gravitational waves from binary black hole inspiral, merger, and ringdown in LIGO-Virgo data from 2009-2010 Author: Aasi, J.;...; Munch, Jesper; Murphy, D.;...; Ottaway, David John; Ottens, R. S.;...; Veitch, Peter John; ... et al.; LIGO Scientific Collaboration; VIRGO Collaboration Abstract: We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a (20,20)M⊙ coalescence was 300 Mpc. No gravitational wave signals were found. We thus report upper limits on the astrophysical coalescence rates of BBH as a function of the component masses for nonspinning components, and also evaluate the dependence of the search sensitivity on component spins aligned with the orbital angular momentum. We find an upper limit at 90% confidence on the coalescence rate of BBH with nonspinning components of mass between 19 and 28M⊙ of 3.3×10⁻⁷ mergers Mpc⁻³yr⁻¹.

Search for photon-linelike signatures from dark matter annihilations with H.E.S.S

2013-05-08T05:01:17Z

Title: Search for photon-linelike signatures from dark matter annihilations with H.E.S.S Author: Abramowski, A.;...; de Wilt, Phoebe Claire; Maxted, Nigel Ivan; Mayer, M.;...; Rowell, Gavin Peter; ... et al.; H.E.S.S. Collaboration Abstract: Gamma-ray line signatures can be expected in the very-high-energy (Eγ>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 γ-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. γ-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 γ-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 ⟨σv⟩χχ→γγ reach ∼10⁻²⁷ cm³ s⁻¹, based on the Einasto parametrization of the Galactic DM halo density profile.

Search for very-high-energy γ-ray emission from Galactic globular clusters with H.E.S.S

2013-05-08T05:29:05Z

Title: Search for very-high-energy γ-ray emission from Galactic globular clusters with H.E.S.S Author: Abramowski, A.;...; de Wilt, Phoebe Claire; Maxted, Nigel Ivan; Mayer, M.;...; Rowell, Gavin Peter; ... et al. Abstract: Context. Globular clusters (GCs) are established emitters of high-energy (HE, 100MeV < E < 100 GeV) γ-ray radiation which could originate from the cumulative emission of the numerous millisecond pulsars (msPSRs) in the clusters' cores or from inverse Compton (IC) scattering of relativistic leptons accelerated in the GC environment. These stellar clusters could also constitute a new class of sources in the very-high-energy (VHE, E > 100 GeV) γ-ray regime, judging from the recent detection of a signal from the direction of Terzan 5 with the H.E.S.S. telescope array. Aims. To search for VHE γ-ray sources associated with other GCs, and to put constraints on leptonic emission models, we systematically analyzed the observations towards 15 GCs taken with the H.E.S.S. array of imaging atmospheric Cherenkov telescopes. Methods. We searched for point-like and extended VHE γ-ray emission from each GC in our sample and also performed a stacking analysis combining the data from all GCs to investigate the hypothesis of a population of faint emitters. Assuming IC emission as the origin of the VHE γ-ray signal from the direction of Terzan 5, we calculated the expected γ-ray flux from each of the 15 GCs, based on their number of millisecond pulsars, their optical brightness and the energy density of background photon fields. Results. We did not detect significant VHE γ-ray emission from any of the 15 GCs in either of the two analyses. Given the uncertainties related to the parameter determinations, the obtained flux upper limits allow to rule out the simple IC/msPSR scaling model for NGC6388 and NGC7078. The upper limits derived from the stacking analyses are factors between 2 and 50 below the flux predicted by the simple leptonic scaling model, depending on the assumed source extent and the dominant target photon fields. Therefore, Terzan 5 still remains exceptional among all GCs, as the VHE γ-ray emission either arises from extra-ordinarily efficient leptonic processes, or from a recent catastrophic event, or is even unrelated to the GC itself.