Alan A. Watson

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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 x 10(19) electron volts and the positions of active galactic nuclei (AGN) lying within approximately 75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these(More)
The arrival directions of extremely high energy cosmic rays (EHECR) above 4 10 19 eV, observed by four surface array experiments in the northern hemisphere, are examined for coincidences from similar directions in the sky. The total number of cosmic rays is 92. A signi cant number of double coincidences (doublet) and triple coincidences (triplet) are(More)
The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) 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(More)
The energy spectrum of cosmic rays above 2.5 x 10;{18} eV, derived from 20,000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the particle flux, J proportional, variantE;{-gamma}, at energies between 4 x 10;{18} eV and 4 x 10;{19} eV is 2.69+/-0.02(stat)+/-0.06(syst), steepening to 4.2+/-0.4(stat)+/-0.06(syst) at(More)
Air showers recorded by the Haverah Park Array during the years 1974–1987 have been reanalysed. For the original estimate of the energy spectrum, a relationship between the ground parameter ρ(600) and the primary energy, as determined by Hillas in the 1970s, was used. Here we describe the energy spectrum obtained using the QGSJET98 interaction model in the(More)
We describe the measurement of the depth of maximum, X{max}, of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above 10;{18} eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was(More)
In this Letter we examine the arrival directions of the most energetic cosmic rays (E > 2 1019 eV) detected by several air shower experiments. We find that data taken by different air shower arrays show positive correlations, indicating a non–uniform arrival direction distribution. We also find that the events with energy > 4 1019 eV exhibit a correlation(More)
It is anticipated that the Pierre Auger Observatory can be used to detect cosmic neutrinos of > 10 eV that arrive at very large zenith angles. However showers created by neutrino interactions close to the detector must be picked out against a background of similar events initiated by cosmic ray nuclei. As a step towards understanding this background, we(More)
We describe a method to analyse inclined air showers produced by ultra high energy cosmic rays using an analytical description of the muon densities. We report the results obtained using data from inclined events (60 < θ < 80) recorded by the Haverah Park shower detector for energies above 10 eV. Using mass independent knowledge of the UHECR spectrum(More)