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Found in: osebi
Keywords: detektor mionov, detektor Čerenkova, AMIGA, P. Auger Observatory
Published: 29.02.2016; Views: 2811; Downloads: 0
Fulltext (9,50 MB)

Abstract: Surface detector array (SD) of the Pierre Auger Observatory has the capability to observe variations in the flux of low energy secondary cosmic ray particles. Flux rates of low energy particles can be obtained either from particle count rates (scaler mode) or from charge distribution of the pulses (histogram mode), detected by individual water Cherenkov detectors (WCD). In scaler mode, SD is sensitive to particles that deposit energy between ∼15 MeV and ∼100 MeV in a WCD, while in histogram mode the deposited energy range can be extended up to ∼1 GeV. These two low energy detection modes are excellent tools for monitoring modulations of the galactic cosmic ray flux, related to solar activity, such as Forbush decreases (with typical duration of several hours to weeks) and Solar cycle (with a duration of several years), as they provide fluxes of cosmic rays with different energies at the same detector. In this contribution we present an analysis of the effects of space weather and space climate on low energy mode data collected by the Pierre Auger Observatory in the period between 2006 and 2013. In particular, we focus on the long term trend of the cosmic ray flux. In addition to the standard corrections for atmospheric effects such as pressure, the analysis takes into account also the corrections for the long term evolution of the response of the surface detectors. Results show good correlation of the corrected low energy mode Auger data with neutron flux measurements by the global neutron monitoring network (NMDB).
Found in: osebi
Keywords: Pierre Auger Observatory, Auger low-energy modes, Solar modulation
Published: 13.06.2017; Views: 2200; Downloads: 131
Fulltext (36,34 KB)

Abstract: The flux of ultra-high energy cosmic rays has been measured with unprecedented precision at the Pierre Auger Observatory. We report an update of the all-sky flux of cosmic rays above 3 x 10 [sup] 17 eV obtained by combining four independent data sets. These measurements are based on data from the surface detector arrays (divided into two sets according to the shower zenith angle), from a nested, denser, detector array, and hybrid events measured simultaneously with both the fluorescence detector and the surface detector array. The spectral features are presented in detail and the systematic uncertainties are addressed. The huge amount of data collected to date, with a total exposure exceeding 50,000 km2 sr yr, together with the wide range of sky observed (in declination from -90[deg] to 45[deg]) also allow us to measure the energy spectrum from different regions of the sky. We present the results of the search for a dependence of the measured flux on the declination of the incoming directions.
Found in: osebi
Keywords: ultra-high energy cosmic rays energy spectrum Pierre Auger Observatory
Published: 02.03.2016; Views: 3231; Downloads: 165
Fulltext (755,08 KB)

Abstract: The large-scale distribution of arrival directions of high-energy cosmic rays carries major clues to understanding their origin. The Pierre Auger Collaboration have implemented different analyses to search for dipolar and quadrupolar anisotropies in different energy ranges spanning four orders of magnitude. A common phase ≈270◦ of the first harmonic modulation in right-ascension was found in adjacent energy intervals below 1 EeV, and another common phase ≈100◦ above 4 EeV. A constancy of phase measurements in ordered energy intervals originating from a genuine anisotropy is expected to appear with a smaller number of events than those needed to achieve significant amplitudes. This led us to design a prescribed test aimed at establishing whether this consistency in phases is real at 99% CL. The test required a total independent exposure of 21,000 km2 sr yr. We report on the status of this prescription. We also report the results of the search for a dipole anisotropy for cosmic rays with energies above 4 EeV using events with zenith angles between 60◦ and 80◦. Compared to previous analyses of events with zenith angles smaller than 60◦, this extension increases the size of the data set by 30%, and enlarges the fraction of exposed sky from 71% to 85%. The largest departure from isotropy is found in the energy range above 8 EeV, with an amplitude for the first harmonic in right ascension r1 = (4.4 ± 1.0) × 10[sup]−2, that has a chance probability P(≥ r1) = 6.4×10[sup]−5, reinforcing the hint previously reported with vertical events alone.
Found in: osebi
Keywords: high-energy cosmic rays large-scale distribution anisotropy studies Pierre Auger Observatory
Published: 02.03.2016; Views: 2655; Downloads: 177
Fulltext (862,90 KB)

Abstract: For the first time the Pierre Auger Collaboration presents〈Xmax〉and σ(Xmax) measurements covering nearly three decades of energy. In this analysis we include new Xmax data obtained with the High Elevation Auger Telescopes (HEAT) enhancement. The HEAT telescopes cover a field of view ranging from 30◦ to 60◦ of elevation and are located next to one of the standard fluorescence detector sites (Coihueco). The combination of the HEAT and Coihueco telescopes covers a field of view from ∼2◦ up to ∼60◦ of elevation. Thus, the combination can sample the longitudinal profile of nearby lower energy showers, allowing us to extend the energy range down to 10[sup]17 eV.
Found in: osebi
Keywords: extensive atmospheric showers, longitudinal shower profile, depth of the shower maximum, Pierre Auger Observatory
Published: 03.03.2016; Views: 2930; Downloads: 173
Fulltext (718,30 KB)