OBSERVATION OF ANISOTROPY IN THE ARRIVAL DIRECTIONS OF GALACTIC COSMIC RAYS AT MULTIPLE ANGULAR SCALES WITH IceCube

Journal Article · Mon Oct 10 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/740/1/16; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21587432

Abbasi, R; Aguilar, J A; Andeen, K; Baker, M ^[1]; Abdou, Y ^[2]; Abu-Zayyad, T ^[3]; Adams, J ^[4]; Ahlers, M ^[5]; Altmann, D ^[6]; Auffenberg, J; Becker, K -H ^[7]; Bai, X ^[8]; Barwick, S W ^[9]; Bay, R ^[10]; Alba, J L. Bazo; Benabderrahmane, M L ^[11]; Beattie, K ^[12]; Beatty, J J ^[13]; Bechet, S ^[14]; Becker, J K ^[15]

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1. Department of Physics, University of Wisconsin, Madison, WI 53706 (United States)
2. Department of Physics and Astronomy, University of Gent, B-9000 Gent (Belgium)
3. Department of Physics, University of Wisconsin, River Falls, WI 54022 (United States)
4. Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch (New Zealand)
5. Department of Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP (United Kingdom)
6. III. Physikalisches Institut, RWTH Aachen University, D-52056 Aachen (Germany)
7. Department of Physics, University of Wuppertal, D-42119 Wuppertal (Germany)
8. Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)
9. Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States)
10. Department of Physics, University of California, Berkeley, CA 94720 (United States)
11. DESY, D-15735 Zeuthen (Germany)
12. Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)
13. Department of Physics and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210 (United States)
14. Universite Libre de Bruxelles, Science Faculty CP230, B-1050 Brussels (Belgium)
15. Fakultaet fuer Physik and Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

Between 2009 May and 2010 May, the IceCube neutrino detector at the South Pole recorded 32 billion muons generated in air showers produced by cosmic rays with a median energy of 20 TeV. With a data set of this size, it is possible to probe the southern sky for per-mil anisotropy on all angular scales in the arrival direction distribution of cosmic rays. Applying a power spectrum analysis to the relative intensity map of the cosmic ray flux in the southern hemisphere, we show that the arrival direction distribution is not isotropic, but shows significant structure on several angular scales. In addition to previously reported large-scale structure in the form of a strong dipole and quadrupole, the data show small-scale structure on scales between 15{sup 0} and 30{sup 0}. The skymap exhibits several localized regions of significant excess and deficit in cosmic ray intensity. The relative intensity of the smaller-scale structures is about a factor of five weaker than that of the dipole and quadrupole structure. The most significant structure, an excess localized at (right ascension {alpha} = 122.{sup 0}4 and declination {delta} = -47.{sup 0}4), extends over at least 20{sup 0} in right ascension and has a post-trials significance of 5.3{sigma}. The origin of this anisotropy is still unknown.

• OSTI ID: 21587432
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 740; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ANISOTROPY
COSMIC RADIATION
COSMIC RAY FLUX
DIPOLES
DISTRIBUTION
GALAXIES
IONIZING RADIATIONS
MULTIPOLES
RADIATION FLUX
RADIATIONS