Indications of anisotropy at large angular scales in the arrival directions of cosmic rays detected at the Pierre Auger Observatory
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
ultra-high energy;cosmic rays;anisotropy studies;large-scale distribution;Pierre Auger Observatory;
Data
| Language: | English |
|---|---|
| Year of publishing: | 2015 |
| Typology: | 1.08 - Published Scientific Conference Contribution |
| Organization: | UNG - University of Nova Gorica |
| UDC: | 539.1 |
| COBISS: |
4150523
|
| ISSN: | 1824-8039 |
| Views: | 4407 |
| Downloads: | 233 |
| Average score: | 0 (0 votes) |
| Metadata: |
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Other data
| URN: | URN:SI:UNG |
|---|---|
| Type (COBISS): | Not categorized |
| Pages: | 8 str. |
| Chronology: | 2015 |
| ID: | 9128055 |
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