0000000001236777
AUTHOR
B. Kégl
A search for point sources of EeV neutrons
A thorough search of the sky exposed at the Pierre Auger Cosmic Ray Observatory reveals no statistically significant excess of events in any small solid angle that would be indicative of a flux of neutral particles from a discrete source. The search covers from −90◦ to +15◦ in declination using four different energy ranges above 1 EeV (1018 eV). The method used in this search is more sensitive to neutrons than to photons. The upper limit on a neutron flux is derived for a dense grid of directions for each of the four energy ranges. These results constrain scenarios for the production of ultrahigh energy cosmic rays in the Galaxy.
Ultra-High Energy Neutrinos at the Pierre Auger Observatory
The observation of ultrahigh energy neutrinos (UHE nu s) has become a priority in experimental astroparticle physics. UHE nu s can be detected with a variety of techniques. In particular, neutrinos can interact in the atmosphere (downward-going nu) or in the Earth crust (Earth-skimming nu), producing air showers that can be observed with arrays of detectors at the ground. With the surface detector array of the Pierre Auger Observatory we can detect these types of cascades. The distinguishing signature for neutrino events is the presence of very inclined showers produced close to the ground (i.e., after having traversed a large amount of atmosphere). In this work we review the procedure and …
Interpretation of the depths of maximum of extensive air showers measured by the Pierre Auger Observatory
To interpret the mean depth of cosmic ray air shower maximum and its dispersion, we parametrize those two observables as functions of the first two moments of the ln A distribution. We examine the goodness of this simple method through simulations of test mass distributions. The application of the parameterization to Pierre Auger Observatory data allows one to study the energy dependence of the mean ln A and of its variance under the assumption of selected hadronic interaction models. We discuss possible implications of these dependences in term of interaction models and astrophysical cosmic ray sources.
The impact of feature extraction on the performance of a classifier : kNN, Naïve Bayes and C4.5
"The curse of dimensionality" is pertinent to many learning algorithms, and it denotes the drastic raise of computational complexity and the classification error in high dimensions. In this paper, different feature extraction techniques as means of (1) dimensionality reduction, and (2) constructive induction are analyzed with respect to the performance of a classifier. Three commonly used classifiers are taken for the analysis: kNN, Naïve Bayes and C4.5 decision tree. One of the main goals of this paper is to show the importance of the use of class information in feature extraction for classification and (in)appropriateness of random projection or conventional PCA to feature extraction for …
Search for patterns by combining cosmic-ray energy and arrival directions at the Pierre Auger Observatory
Energy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with E ≥ 6×1019 eV by analyzing cosmic rays with energies above E ≥ 5×1018 eV arriving within an angular separation of approximately 15∘. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis. The comparison of these measurements with …
Searches for anisotropies in the arrival directions of the highest energy cosmic rays detected by the Pierre Auger Observatory
We analyze the distribution of arrival directions of ultra-high energy cosmic rays recorded at the Pierre Auger Observatory in 10 years of operation. The data set, about three times larger than that used in earlier studies, includes arrival directions with zenith angles up to $80^\circ$, thus covering from $-90^\circ$ to $+45^\circ$ in declination. After updating the fraction of events correlating with the active galactic nuclei (AGNs) in the V��ron-Cetty and V��ron catalog, we subject the arrival directions of the data with energies in excess of 40 EeV to different tests for anisotropy. We search for localized excess fluxes and for self-clustering of event directions at angular scales up t…
Measurement of the cosmic ray energy spectrum using hybrid events of the Pierre Auger Observatory
The energy spectrum of ultra-high energy cosmic rays above 10$^{18}$ eV is measured using the hybrid events collected by the Pierre Auger Observatory between November 2005 and September 2010. The large exposure of the Observatory allows the measurement of the main features of the energy spectrum with high statistics. Full Monte Carlo simulations of the extensive air showers (based on the CORSIKA code) and of the hybrid detector response are adopted here as an independent cross check of the standard analysis (Phys. Lett. B 685, 239 (2010)). The dependence on mass composition and other systematic uncertainties are discussed in detail and, in the full Monte Carlo approach, a region of confiden…
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays. It consists of a surface array to measure secondary particles at ground level and a fluorescence detector to measure the development of air showers in the atmosphere above the array. The ‘‘hybrid” detection mode combines the information from the two subsystems. We describe the determination of the hybrid exposure for events observed by the fluorescence telescopes in coincidence with at least one water-Cherenkov detector of the surface array. A detailed knowledge of the time dependence of the detection operations is crucial for an accurate evaluation of the exposure. We discuss the relevance of monitoring data coll…
Erratum to "Atmospheric effects on extensive air showers observed with the surface detector of the Pierre Auger observatory"[Astroparticle Physics 32(2) (2009), 89-99]
The Pierre Auger Collaboration... K.B. Barber... J.A. Bellido... R.W. Clay... B.R. Dawson... V.C. Holmes... J. Sorokin... P. Wahrlich... B.J. Whelan... M.G. Winnick... et al.
Measurement of the Depth of Maximum of Extensive Air Showers above 10(18) eV
We describe the measurement of the depth of maximum, Xmax, of the longitudinal development of air showers induced by cosmic rays. Almost four thousand events above 10¹⁸ 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 found to evolve with energy at a rate of (106⁺³⁵₋₂₁) g/cm²/decade below 1018.24 ± 0.05 eV and (24 ± 3) g/cm²/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm². The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.
A search for point sources of EeV photons
Measurements of air showersmade using the hybrid technique developed with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for point sources of EeV photons anywhere in the exposed sky. A multivariate analysis reduces the background of hadronic cosmic rays. The search is sensitive to a declination band from −85º to +20º, in an energy range from 1017.3 eV to 1018.5 eV. No photon point source has been detected. An upper limit on the photon flux has been derived for every direction. The mean value of the energy flux limit that results from this, assuming a photon spectral index of −2, is 0.06 eV cm−2 s−1, and no celestial direction exceeds 0.25 eV …
Origin of atmospheric aerosols at the Pierre Auger Observatory using studies of air mass trajectories in South America
The Pierre Auger Observatory is making significant contributions towards understanding the nature and origin of ultra-high energy cosmic rays. One of its main challenges is the monitoring of the atmosphere, both in terms of its state variables and its optical properties. The aim of this work is to analyze aerosol optical depth $\tau_{\rm a}(z)$ values measured from 2004 to 2012 at the observatory, which is located in a remote and relatively unstudied area of the Pampa Amarilla, Argentina. The aerosol optical depth is in average quite low - annual mean $\tau_{\rm a}(3.5~{\rm km})\sim 0.04$ - and shows a seasonal trend with a winter minimum - $\tau_{\rm a}(3.5~{\rm km})\sim 0.03$ -, and a sum…
Reconstruction of inclined air showers detected with the Pierre Auger Observatory
We describe the method devised to reconstruct inclined cosmic-ray air showers with zenith angles greater than $60^\circ$ detected with the surface array of the Pierre Auger Observatory. The measured signals at the ground level are fitted to muon density distributions predicted with atmospheric cascade models to obtain the relative shower size as an overall normalization parameter. The method is evaluated using simulated showers to test its performance. The energy of the cosmic rays is calibrated using a sub-sample of events reconstructed with both the fluorescence and surface array techniques. The reconstruction method described here provides the basis of complementary analyses including an…