Research Article

Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 × 1018 eV

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Science  22 Sep 2017:
Vol. 357, Issue 6357, pp. 1266-1270
DOI: 10.1126/science.aan4338
  • Fig. 1 Normalized rate of events as a function of right ascension.

    Normalized rate for 32,187 events with E ≥ 8 EeV, as a function of right ascension (integrated in declination). Error bars are 1σ uncertainties. The solid line shows the first-harmonic modulation from Table 1, which displays good agreement with the data (χ2/n = 10.5/10); the dashed line shows a constant function.

  • Fig. 2 Map showing the fluxes of particles in equatorial coordinates.

    Sky map in equatorial coordinates, using a Hammer projection, showing the cosmic-ray flux above 8 EeV smoothed with a 45° top-hat function. The galactic center is marked with an asterisk; the galactic plane is shown by a dashed line.

  • Fig. 3 Map showing the fluxes of particles in galactic coordinates.

    Sky map in galactic coordinates showing the cosmic-ray flux for E ≥ 8 EeV smoothed with a 45° top-hat function. The galactic center is at the origin. The cross indicates the measured dipole direction; the contours denote the 68% and 95% confidence level regions. The dipole in the 2MRS galaxy distribution is indicated. Arrows show the deflections expected for a particular model of the galactic magnetic field (8) on particles with E/Z = 5 or 2 EeV.

  • Table 1 First harmonic in right ascension.

    Data are from the Rayleigh analysis of the first harmonic in right ascension for the two energy bins.

    Energy
    (EeV)
    Number
    of events
    Fourier
    coefficient aα
    Fourier
    coefficient bα
    Amplitude
    rα
    Phase
    ϕα (°)
    Probability
    P (≥ rα)
    4 to 881,7010.001 ± 0.0050.005 ± 0.005Embedded Image80 ± 600.60
    ≥832,187−0.008 ± 0.0080.046 ± 0.008Embedded Image100 ± 102.6 × 10−8
  • Table 2 Three-dimensional dipole reconstruction.

    Directions of dipole components are shown in equatorial coordinates.

    Energy
    (EeV)
    Dipole
    component dz
    Dipole
    component d
    Dipole
    amplitude d
    Dipole
    declination δd (°)
    Dipole right
    ascension αd (°)
    4 to 8−0.024 ± 0.009Embedded ImageEmbedded ImageEmbedded Image80 ± 60
    ≥8−0.026 ± 0.015Embedded ImageEmbedded ImageEmbedded Image100 ± 10

Supplementary Materials

  • Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 Ã- 1018 eV

    The Pierre Auger Collaboration

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods 
    • Supplementary Text 
    • Figs. S1 to S4 
    • Table S1

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