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251.
Indications of anisotropy at large angular scales in the arrival directions of cosmic rays detected at the Pierre Auger Observatory
Imen Al Samarai, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, published scientific conference contribution

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.
Keywords: high-energy cosmic rays large-scale distribution anisotropy studies Pierre Auger Observatory
Published in RUNG: 02.03.2016; Views: 5275; Downloads: 239
.pdf Full text (862,90 KB)

252.
Arrival directions of the highest-energy cosmic rays detected with the Pierre Auger Observatory
Julien Aublin, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, published scientific conference contribution

Abstract: We present the results of a search for small to intermediate scale anisotropies in the distribution of arrival directions of ultra-high energy cosmic rays recorded at the Pierre Auger Observatory. The data set, gathered in ten years of operation, includes arrival directions with zenith angles up to 80◦, and is about three times larger than that used in earlier studies. We update the test based on correlations with active galactic nuclei (AGNs) from the Véron-Cetty and Véron catalog, which does not yield a significant indication of anisotropy with the present data set. We perform a blind search for localized excess fluxes and for self-clustering of arrival directions at angular scales up to 30◦ and for different energy thresholds between 40 EeV and 80 EeV. We also examine the correlation of arrival directions with relatively nearby galaxies in the 2MRS catalog, AGNs detected by Swift-BAT, and a sample of radio galaxies with jets and with the Centaurus A galaxy. None of the searches shows a statistically significant evidence of anisotropy. The two largest departures from isotropy that were found have a post-trial probability ≈ 1.4%. One is for cosmic rays with energy above 58 EeV that arrive within 15◦ of the direction toward Centaurus A. The other is for arrival directions within 18◦ of Swift-BAT AGNs closer than 130 Mpc and brighter than 10[sup]44 erg/s, with the same energy threshold.
Keywords: ultra-high energy cosmic rays anisotropy studies active galactic nuclei Pierre Auger Observatory
Published in RUNG: 02.03.2016; Views: 5310; Downloads: 231
.pdf Full text (1,32 MB)

253.
The flux of ultra-high energy cosmic rays after ten years of operation of the Pierre Auger Observatory
Inés Valiño, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, published scientific conference contribution

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.
Keywords: ultra-high energy cosmic rays energy spectrum Pierre Auger Observatory
Published in RUNG: 02.03.2016; Views: 5811; Downloads: 226
.pdf Full text (755,08 KB)

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