Full sky harmonic analysis hints at large UHECR deflections
arXiv:1411.2486 · doi:10.1134/S1063776115030231
Abstract
The full-sky multipole coefficients of the ultra-high energy cosmic ray (UHECR) flux have been measured for the first time by the Pierre Auger and Telescope Array collaborations using a joint data set with E > 10 EeV. We calculate these harmonic coefficients in the model where UHECR are protons and sources trace the local matter distribution, and compare our results with observations. We find that the expected power for low multipoles (dipole and quadrupole, in particular) is sytematically higher than in the data: the observed flux is too isotropic. We then investigate to which degree our predictions are influenced by UHECR deflections in the regular Galactic magnetic field (GMF). It turns out that the UHECR power spectrum coefficients are quite insensitive to the effects of the GMF, so it is unlikely that the discordance can be reconciled by tuning the GMF model. On the contrary, a sizeable fraction of uniformly distributed flux (representing for instance an admixture of heavy nuclei with considerably larger deflections) can bring simulations and observations to an accord.
8 pages, 4 figures and one table, JETPL style -- v2 as published in JETPL
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- How isotropic can the UHECR flux be?
- Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory
- On the anisotropy in the arrival directions of ultra-high-energy cosmic rays
- Large-scale cosmic ray anisotropies with 19 years of data from the Pierre Auger Observatory
- Constraints on UHECR sources and extragalactic magnetic fields from directional anisotropies
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- Detection prospects of the Telescope Array hotspot by space observatories
- Constraining ultra-high-energy cosmic ray composition through cross-correlations
- Modelling cross-correlations of ultra-high-energy cosmic rays and galaxies
- Neutrino anisotropy as a probe of extreme astrophysical accelerators