Small-scale anisotropy of cosmic rays above 10^19ev observed with the akeno giant air shower array
Feb, 1999
40 pages
Published in:
- Astrophys.J. 522 (1999) 225-237
e-Print:
- astro-ph/9902239 [astro-ph]
DOI:
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Abstract: (arXiv)
With the Akeno Giant Air Shower Array (AGASA), 581 cosmic rays above 10^19eV, 47 above 4 x 10^19eV, and 7 above 10^20eV are observed until August 1998. Arrival direction distribution of these extremely high energy cosmic rays has been studied. While no significant large-scale anisotropy is found on the celestial sphere, some interesting clusters of cosmic rays are observed. Above 4 x 10^19eV, there are one triplet and three doublets within separation angle of 2.5^o and the probability of observing these clusters by a chance coincidence under an isotropic distribution is smaller than 1 %. Especially the triplet is observed against expected 0.05 events. The cos(\theta_GC) distribution expected from the Dark Matter Halo model fits the data as well as an isotropic distribution above 2 x 10^19eV and 4 x 10^19eV, but is a poorer fit than isotropy above 10^19eV. Arrival direction distribution of seven 10^20eV cosmic rays is consistent with that of lower energy cosmic rays and is uniform. Three of seven are members of doublets above about 4 x 10^19eV.- cosmic radiation: angular distribution
- cosmic radiation: anisotropy
- cosmic radiation: energy spectrum
- cosmic radiation: particle source
- shower detector: experimental results
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