Searches for Large-Scale Anisotropy in the Arrival Directions of Cosmic Rays Detected above Energy of $10^{19}$ eV at the Pierre Auger Observatory and the Telescope Array

Spherical harmonic moments are well-suited for capturing anisotropy at any scale in the flux of cosmic rays. An unambiguous measurement of the full set of spherical harmonic coefficients requires full-sky coverage. This can be achieved by combining data from observatories located in both the norther...

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Bibliographic Details
Published in:The Astrophysical journal 2014-10, Vol.794 (2)
Main Authors: Aab, A., Aublin, J., Billoir, P., Blanco, M., Caccianiga, L., Dallier, Richard, Gaior, R., Gate, F., Ghia, P. L., Lautridou, Pascal, Letessier-Selvon, A., Maller, J., Marin, V., Martin, Lilian, Münchmeyer, M., Ravel, O., Revenu, Benoît, Settimo, M., Cordier, A., Garcia-Gamez, D., Kégl, Balázs, Monnier Ragaigne, D., Veberic, D., Avenier, M., Berat, C., Le Coz, S., Lebrun, D., Louedec, K., Montanet, F., Stutz, A., Tartare, M., Samarai, Imen Al, Deligny, O., Salamida, F., Suomijärvi, T., Lhenry-Yvon, I., Martraire, D.
Format: Article
Language:English
Subjects:
AMPLITUDES
ANISOTROPY
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
COSMIC RADIATION
DIPOLES
EXPANSION
High Energy Astrophysical Phenomena
Instrumentation and Methods for Astrophysic
Physics
QUADRUPOLE MOMENTS
Sciences of the Universe
SPECTRA
SPHERICAL CONFIGURATION
SYMMETRY
TELESCOPES
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Summary:Spherical harmonic moments are well-suited for capturing anisotropy at any scale in the flux of cosmic rays. An unambiguous measurement of the full set of spherical harmonic coefficients requires full-sky coverage. This can be achieved by combining data from observatories located in both the northern and southern hemispheres. To this end, a joint analysis using data recorded at the Telescope Array and the Pierre Auger Observatory above $10^{19}$ eV is presented in this work. The resulting multipolar expansion of the flux of cosmic rays allows us to perform a series of anisotropy searches, and in particular to report on the angular power spectrum of cosmic rays above $10^{19}$ eV. No significant deviation from isotropic expectations is found throughout the analyses performed. Upper limits on the amplitudes of the dipole and quadrupole moments are derived as a function of the direction in the sky, varying between 7% and 13% for the dipole and between 7% and 10% for a symmetric quadrupole.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/794/2/172