# Full sky harmonic analysis hints at large ultra-high energy cosmic ray deflections

## 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. It turns out that the UHECR power spectrum coefficients C{sub l} are quite insensitive to the effects of the Galactic magnetic field, so it is unlikely that the discordance can be reconciled by tuning the Galactic magnetic field 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.

- Authors:

- Université Libre de Bruxelles, Service de Physique Théorique (Belgium)

- Publication Date:

- OSTI Identifier:
- 22472364

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Experimental and Theoretical Physics; Journal Volume: 120; Journal Issue: 3; Other Information: Copyright (c) 2015 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; COSMIC PROTONS; COSMIC RAY FLUX; COSMIC RAY SOURCES; DIPOLES; EEV RANGE; ENERGY SPECTRA; HEAVY NUCLEI; INTERSTELLAR MAGNETIC FIELDS; MILKY WAY; TELESCOPES; TUNING

### Citation Formats

```
Tinyakov, P. G., E-mail: petr.tiniakov@ulb.ac.be, and Urban, F. R., E-mail: furban@ulb.ac.be.
```*Full sky harmonic analysis hints at large ultra-high energy cosmic ray deflections*. United States: N. p., 2015.
Web. doi:10.1134/S1063776115030231.

```
Tinyakov, P. G., E-mail: petr.tiniakov@ulb.ac.be, & Urban, F. R., E-mail: furban@ulb.ac.be.
```*Full sky harmonic analysis hints at large ultra-high energy cosmic ray deflections*. United States. doi:10.1134/S1063776115030231.

```
Tinyakov, P. G., E-mail: petr.tiniakov@ulb.ac.be, and Urban, F. R., E-mail: furban@ulb.ac.be. Sun .
"Full sky harmonic analysis hints at large ultra-high energy cosmic ray deflections". United States.
doi:10.1134/S1063776115030231.
```

```
@article{osti_22472364,
```

title = {Full sky harmonic analysis hints at large ultra-high energy cosmic ray deflections},

author = {Tinyakov, P. G., E-mail: petr.tiniakov@ulb.ac.be and Urban, F. R., E-mail: furban@ulb.ac.be},

abstractNote = {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. It turns out that the UHECR power spectrum coefficients C{sub l} are quite insensitive to the effects of the Galactic magnetic field, so it is unlikely that the discordance can be reconciled by tuning the Galactic magnetic field 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.},

doi = {10.1134/S1063776115030231},

journal = {Journal of Experimental and Theoretical Physics},

number = 3,

volume = 120,

place = {United States},

year = {Sun Mar 15 00:00:00 EDT 2015},

month = {Sun Mar 15 00:00:00 EDT 2015}

}