THE LARGE-SCALE COSMIC-RAY ANISOTROPY AS OBSERVED WITH MILAGRO

By A. Abdo, B. Allen, T. Aune, D. Berley, S. Casanova, Changqi Chen, B. Dingus, R. Ellsworth, L. Fleysher, R. Fleysher and 23 more. 2008

196 citations recorded by the source corpus.

Results are presented of a harmonic analysis of the large-scale cosmic-ray (CR) anisotropy as observed by the Milagro observatory. We show a two-dimensional display of the sidereal anisotropy projections in right ascension (R.A.) generated by the fitting of three harmonics to 18 separate declination bands. The Milagro observatory is a water Cherenkov detector located in the Jemez mountains near Los Alamos, New Mexico. With a high duty cycle and large field of view, Milagro is an excellent instrument for measuring this anisotropy with high sensitivity at TeV energies. The analysis is conducted using a seven-year data sample consisting of more than 95 billion events, the largest such data set in existence. We observe an anisotropy with a magnitude around 0.1% for CRs with a median energy of 6 TeV. The dominant feature is a deficit region of depth (2.49 ± 0.02 stat. ± 0.09 sys.) ×10−3 in the direction of the Galactic north pole centered at 189 deg R.A. We observe a steady increase in the magnitude of the signal over seven years.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d50d24c39d3e43bc28725897ecc928fdc06f7fc4

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In Astronomy and Astrophysics

1. J. Clem
2. P. Serpico
3. J. Hinton
4. S. Profumo
5. S. Casanova
6. T. Linden
7. S. Buitink
8. Anna Franckowiak

In Nuclear and High Energy Physics

1. J. Clem
2. P. Serpico
3. A. Fedynitch
4. S. Profumo
5. Todor Stanev
6. J. Hinton
7. W. Rhode
8. S. Casanova

Citations in the corpus

• Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory (2017, background): “The anisotropy in cosmic-ray arrival direction is subdominant at ∼10−3 (Abdo et al. 2009), and we can conclude that the exposure is flat to within ±2%.”
• Sensitivity of the high altitude water Cherenkov detector to sources of multi-TeV gamma rays (2013, unknown): “These cosmic rays arrive nearly isotropically, with anisotropy present at a 10 3 level [10,11].”
• OBSERVATION OF ANISOTROPY IN THE GALACTIC COSMIC-RAY ARRIVAL DIRECTIONS AT 400 TeV WITH ICECUBE (2011, background): “…underground and surface array experiments in the Northern hemisphere have shown that a sidereal anisotropy is present in the TeV energy range (Tibet Air Shower gamma (ASγ) array (Amenomori et al. 2006), SuperKamiokande (Guillian et al. 2007), Milagro (Abdo et al. 2009), and ARGO-YBJ (Zhang 2009)).”
• PROBING THE PULSAR ORIGIN OF THE ANOMALOUS POSITRON FRACTION WITH AMS-02 AND ATMOSPHERIC CHERENKOV TELESCOPES (2013, background): “While the exact magnitude of this anisotropy is difficult to ascertain, as mea- 8 surements by MILAGRO (Abdo et al. 2009) and ICECUBE (Abbasi et al. 2009, 2010) measured the proton anisotropy for median proton energies of 6 TeV and 20 TeV respectively.”
• MEASUREMENT OF THE ANISOTROPY OF COSMIC-RAY ARRIVAL DIRECTIONS WITH ICECUBE (2010, background): “Figure 2 shows an anisotropy that appears to be a continuation of a similar modulation of the cosmic ray flux observed in the Northern hemisphere (Amenomori et al. 2006; Guillian et al. 2007; Abdo et al. 2009).”
• Astrophysical models for the origin of the positron (2011, background): “Thus, it is worth remembering that knowledge in this field does not automatically follows from the collection of more data: an example is provided by the puzzling observations of (hadronic) CR multi-TeV anisotropy from many experiments [145, 146, 147, 148, 149, 150], for which no convincing explanat”