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Title:Indications of anisotropy at large angular scales in the arrival directions of cosmic rays detected at the Pierre Auger Observatory
Authors:Al Samarai, Imen (Author)
Filipčič, Andrej (Author)
Kukec Mezek, Gašper (Author)
Saleh, Ahmed (Author)
Stanič, Samo (Author)
Trini, Marta (Author)
Veberič, Darko (Author)
Vorobiov, Serguei (Author)
Yang, Lili (Author)
Zavrtanik, Danilo (Author)
Zavrtanik, Marko (Author)
et al.
Files:.pdf ICRC2015_372.pdf (862,90 KB)
 
Language:English
Work type:Not categorized (r6)
Tipology:1.08 - Published Scientific Conference Contribution
Organization:UNG - University of Nova Gorica
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
Year of publishing:2015
COBISS_ID:4150523 Link is opened in a new window
URN:URN:SI:UNG:REP:IXMK901I
License:CC BY-NC-SA 4.0
This work is available under this license: Creative Commons Attribution Non-Commercial Share Alike 4.0 International
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Record is a part of a monograph

Title:The 34th International Cosmic Ray Conference
Subtitle:ICRC 2015 (The Hague, Netherlands)
Publisher:PoS, http://pos.sissa.it/
Conference organizer:International Union of Pure and Applied Physics (IUPAP)
Collection title:Proceedings of ICRC 2015
Year of publishing:2015

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