71 research outputs found

    Search for signatures of magnetically-induced alignment in the arrival directions measured by the Pierre Auger Observatory

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    We present the results of an analysis of data recorded at the Pierre Auger Observatory in which we search for groups of directionally-aligned events (or 'multiplets') which exhibit a correlation between arrival direction and the inverse of the energy. These signatures are expected from sets of events coming from the same source after having been deflected by intervening coherent magnetic fields. The observation of several events from the same source would open the possibility to accurately reconstruct the position of the source and also measure the integral of the component of the magnetic field orthogonal to the trajectory of the cosmic rays. We describe the largest multiplets found and compute the probability that they appeared by chance from an isotropic distribution. We find no statistically significant evidence for the presence of multiplets arising from magnetic deflections in the present data. © 2011 Elsevier B.V. All rights reserved.P. Abreu... K. B. Barber... J. A. Bellido... R. W. Clay... A. E. Herve... et al.http://www.journals.elsevier.com/astroparticle-physics

    Description of atmospheric conditions at the Pierre Auger Observatory using the Global Data Assimilation System (GDAS)

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    Atmospheric conditions at the site of a cosmic ray observatory must be known for reconstructing observed extensive air showers. The Global Data Assimilation System (GDAS) is a global atmospheric model predicated on meteorological measurements and numerical weather predictions. GDAS provides altitude-dependent profiles of the main state variables of the atmosphere like temperature, pressure, and humidity. The original data and their application to the air shower reconstruction of the Pierre Auger Observatory are described. By comparisons with radiosonde and weather station measurements obtained on-site in Malargüe and averaged monthly models, the utility of the GDAS data is shown. © 2012 Elsevier B.V. All rights reserved.The Pierre Auger Collaboration... K. B. Barber... J. A. Bellido... R. W. Clay... M. J. Cooper... B. R. Dawson... T. A. Harrison... A. E. Herve... V. C. Holmes... J. Sorokin... P. Wahrlich... B. J. Whelan... et al

    The Lateral Trigger Probability function for the Ultra-High Energy Cosmic Ray showers detected by the Pierre Auger Observatory

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    In this paper we introduce the concept of Lateral Trigger Probability (LTP) function, i.e., the probability for an Extensive Air Shower (EAS) to trigger an individual detector of a ground based array as a function of distance to the shower axis, taking into account energy, mass and direction of the primary cosmic ray. We apply this concept to the surface array of the Pierre Auger Observatory consisting of a 1.5 km spaced grid of about 1600 water Cherenkov stations. Using Monte Carlo simulations of ultra-high energy showers the LTP functions are derived for energies in the range between 1017 and 1019 eV and zenith angles up to 65°. A parametrization combining a step function with an exponential is found to reproduce them very well in the considered range of energies and zenith angles. The LTP functions can also be obtained from data using events simultaneously observed by the fluorescence and the surface detector of the Pierre Auger Observatory (hybrid events). We validate the Monte Carlo results showing how LTP functions from data are in good agreement with simulations. © 2011 Published by Elsevier B.V.The Pierre Auger Collaboration... P. Abreu... K. B. Barber... J. A. Bellido... R. W. Clay... M. J. Cooper... B. R. Dawson... A. E. Herve... V. C. Holmes... J. S. Sorokin... P. S. Wahrlich... M. G. Winnick... et al.http://www.journals.elsevier.com/astroparticle-physics

    Measurement of the energy spectrum of cosmic rays above 10(18) eV using the Pierre Auger Observatory

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    We report a measurement of the flux of cosmic rays with unprecedented precision and statistics using the Pierre Auger Observatory. Based on fluorescence observations in coincidence with at least one surface detector we derive a spectrum for energies above 10¹⁸ eV. We also update the previously published energy spectrum obtained with the surface detector array. The two spectra are combined addressing the systematic uncertainties and, in particular, the influence of the energy resolution on the spectral shape. The spectrum can be described by a broken power law E−γ with index γ=3.3 below the ankle which is measured at log10(Eankle/eV)=18.6. Above the ankle the spectrum is described by a power law with index 2.6 followed by a flux suppression, above about log10(E/eV)=19.5, detected with high statistical significance.J. Abraham... K. B. Barber... J. A. Bellido... R. W. Clay... M. J. Cooper... B. R. Dawson... A. E. Herve... V. C. Holmes... J. Sorokin... P. Wahrlich... B. J. Whelan... M. G. Winnick..

    Measurement of the proton-air cross section at root s=57 TeV with the Pierre Auger Observatory

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    We report a measurement of the proton-air cross section for particle production at the center-of-mass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analyzing the tail of the distribution of the shower maxima, a proton-air cross section of [505±22(stat)₋₃₆⁺²⁸(syst)]  mb is found.K. B Barber.... J.A. Bellido.... R.W. Clay.... M.J. Cooper.... B.R. Dawson.... T.A. Harrison.... A.E. Herve.... V.C. Holmes.... J. Sorokin.... P. Wahrlich.... B.J. Whelan.... M. G. Winnick... et al.(The Pierre Auger Collaboration

    The Pierre Auger Observatory IV: Operation and Monitoring

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    Contributions of the Auger Collaboration to the 32nd International Cosmic Ray Conference, Beijing, August, 2011: Technical reports on operations and monitoring of the Pierre Auger Observator

    Erratum to "The Lateral Trigger Probability function for the Ultra-High Energy Cosmic Ray Showers detected by the Pierre Auger Observatory" [Astroparticle Physics 35 (2011) 266–276]

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    The Pierre Auger Collaboration... K.B. Barber... J.A. Bellido... R.W. Clay... M.J. Cooper... B.R. Dawson... A.E. Herve... V.C. Holmes... J. Sorokin... P. Wahrlich... B.J. Whelan... M.G. Winnick... et al

    Measurement of the Proton-Air Cross Section at root s=57 TeV with the Pierre Auger Observatory

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    Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

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    Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, 6 x 10(19) eV. The anisotropy was measured by the fraction of arrival directions that are less than 3.1 degrees from the position of an active galactic nucleus within 75 Mpc (using the Veron-Cetty and Veron 12th catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is (38(-6)(+7))%, compared with 21% expected for isotropic cosmic rays. This is down from the early estimate of (69-(+11)(13))%. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation. (C) 2010 Elsevier B.V. All rights reserved

    The Pierre Auger Observatory scaler mode for the study of solar activity modulation of galactic cosmic rays

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    Since data-taking began in January 2004, the Pierre Auger Observatory has been recording the count rates of low energy secondary cosmic ray particles for the self-calibration of the ground detectors of its surface detector array. After correcting for atmospheric effects, modulations of galactic cosmic rays due to solar activity and transient events are observed. Temporal variations related with the activity of the heliosphere can be determined with high accuracy due to the high total count rates. In this study, the available data are presented together with an analysis focused on the observation of Forbush decreases, where a strong correlation with neutron monitor data is found
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