13 research outputs found
Observation of the Suppression of the Flux of Cosmic Rays above 4 x 10^19 eV
The energy spectrum of cosmic rays above 2.5×1018eV, derived from 20000 events recorded at the Pierre Auger Observatory, is described. The spectral index γ of the particle flux, JE-γ, at energies between 4×1018eV and 4×1019eV is 2.69±0.02(stat)±0.06(syst), steepening to 4.2±0.4(stat)±0.06(syst) at higher energies. The hypothesis of a single power law is rejected with a significance greater than 6 standard deviations. The data are consistent with the prediction by Greisen and by Zatsepin and Kuz'min
Upper Limit on the Diffuse Flux of UHE tau neutrinos from the Pierre Auger Observatory.
The surface detector array of the Pierre Auger Observatory is sensitive to
Earth-skimming tau-neutrinos that interact in the Earth's crust. Tau
leptons from charged-current interactions can emerge and decay in
the atmosphere to produce a nearly horizontal shower with a significant
electromagnetic component. The data collected between 1 January 2004 and 31
August 2007 is used to place an upper limit on the diffuse flux of
at EeV energies. Assuming an differential energy spectrum the
limit set at 90 % C.L. is GeV cm s sr in the energy range
eV.Comment: 14 pages, 3 figure
Correlation of the highest-energy cosmic rays with nearby extragalactic objects
Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 × 1019 electron volts and the positions of active galactic nuclei (AGN) lying within ∼75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest-energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic background radiation. AGN or objects having a similar spatial distribution are possible sources
Correlation of the Highest-energy Cosmic Rays with the Positions of Nearby Active Galactic Nuclei.
Data collected by the Pierre Auger Observatory provide evidence for
anisotropy in the arrival directions of the cosmic rays with the highest
energies, which are correlated with the positions of relatively nearby active
galactic nuclei (AGN) \cite{science}. The correlation has maximum significance
for cosmic rays with energy greater than ~ 6x10^{19}$ eV and AGN at a distance
less than ~ 75 Mpc. We have confirmed the anisotropy at a confidence level of
more than 99% through a test with parameters specified {\em a priori}, using an
independent data set. The observed correlation is compatible with the
hypothesis that cosmic rays with the highest energies originate from
extra-galactic sources close enough so that their flux is not significantly
attenuated by interaction with the cosmic background radiation (the
Greisen-Zatsepin-Kuz'min effect). The angular scale of the correlation observed
is a few degrees, which suggests a predominantly light composition unless the
magnetic fields are very weak outside the thin disk of our galaxy. Our present
data do not identify AGN as the sources of cosmic rays unambiguously, and other
candidate sources which are distributed as nearby AGN are not ruled out. We
discuss the prospect of unequivocal identification of individual sources of the
highest-energy cosmic rays within a few years of continued operation of the
Pierre Auger Observatory.Comment: 33 pages, 8 figures, submitted to Astropart. phys. Now match the
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