Full-sky searches for anisotropies in UHECR arrival directions with the Pierre Auger Observatory and the Telescope Array

Abstract

The arrival directions of ultra-high-energy cosmic rays appear to be approximately isotropically distributed over the whole sky, but the last-generation UHECR detector arrays, the Pierre Auger Observatory (Auger) and the Telescope Array (TA), have detected thousands of events, allowing us to study small deviations from isotropy. So far, Auger has detected a large-scale anisotropy consistent with a $\sim 6.5\%$ dipole moment in the distribution of cosmic rays with $E>8$~EeV, and both collaborations have reported indications for smaller-scale anisotropies at higher energies. On the other hand, neither array has full-sky coverage, the Auger field of view being limited to declinations $\delta <+45^{\circ }$ and the TA one to $\delta >-16^{\circ }$. Searches for anisotropies with full-sky coverage thus require combining data from both arrays. A working group with members from both collaborations has been established for this task. Since even a minor systematic error in the energy determinations at either of the arrays could result in a sizeable spurious anisotropy along the north--south axis, we devised a method to cross-calibrate the energy scales of the two experiments with respect to each other by using events in a declination band within the intersection of their fields of view. In this contribution, we report on both updates on blind searches for anisotropies and the first full-sky studies of flux models based on possible local extragalactic sources.

8 pages, 6 figures; presented at the 36th International Cosmic Ray Conference (ICRC 2019), 24 July--1 August 2019, Madison, Wisconsin, USA

References in corpus (3)

• Constraints on the origin of cosmic rays above $10^{18}$ eV from large scale anisotropy searches in data of the Pierre Auger Observatory
• AugerPrime: the Pierre Auger Observatory Upgrade
• A Council of Giants

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• Energetics of ultrahigh-energy cosmic-ray nuclei
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• Ultrahigh-energy dipole and beyond
• Echoes of the past: ultra-high energy cosmic rays accelerated by radio galaxies, scattered by starburst galaxies
• Explaining the UHECR spectrum, composition and large-scale anisotropies with radio galaxies
• Latest results of ultra-high-energy cosmic ray measurements with prototypes of the Fluorescence detector Array of Single-pixel Telescopes (FAST)