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A new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival
directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals
from strong, nearby sources. The data consist of 5514 events above 20 EeV with zenith angles up to 80°recorded
before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray
emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies
from a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies from
the Swift-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density
constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical
objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A
maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of
each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of
isotropy with a statistical significance of 4.0σ, the highest value of the test statistic being for energies above
39 EeV. The three alternative models are favored against isotropy with 2.7σ–3.2σ significance. The origin of the
indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed.
Aab, A., Abreu, P., Aglietta, M., Albuquerque, I.F.M., Allekotte, I., Almela, A., et al. (2018). An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources. THE ASTROPHYSICAL JOURNAL LETTERS, 853-L29, 1-10 [10.3847/2041-8213/aaa66d].
An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources
A new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival
directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals
from strong, nearby sources. The data consist of 5514 events above 20 EeV with zenith angles up to 80°recorded
before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray
emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies
from a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies from
the Swift-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density
constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical
objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A
maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of
each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of
isotropy with a statistical significance of 4.0σ, the highest value of the test statistic being for energies above
39 EeV. The three alternative models are favored against isotropy with 2.7σ–3.2σ significance. The origin of the
indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed.
Aab, A., Abreu, P., Aglietta, M., Albuquerque, I.F.M., Allekotte, I., Almela, A., et al. (2018). An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources. THE ASTROPHYSICAL JOURNAL LETTERS, 853-L29, 1-10 [10.3847/2041-8213/aaa66d].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10447/547054
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