Searches for Anisotropies in the Arrival Directions of the Highest Energy Cosmic Rays Detected by the Pierre Auger Observatory

Abstract

We analyze the distribution of arrival directions of ultra-high energy cosmic rays recorded at the Pierre Auger Observatory in 10 years of operation. The data set, about three times larger than that used in earlier studies, includes arrival directions with zenith angles up to 80 • , thus covering from −90 • to +45 • in declination. After updating the fraction of events correlating with the active galactic nuclei (AGNs) in the Véron-Cetty and Véron catalog, we subject the arrival directions of the data with energies in excess of 40 EeV to different tests for anisotropy. We search for localized excess fluxes and for self-clustering of event directions at angular scales up to 30 • and for different threshold energies between 40 EeV and 80 EeV. We then look for correlations of cosmic rays with celestial structures both in the Galaxy (the Galactic Center and Galactic Plane) and in the local Universe (the Super-Galactic Plane). We also examine their correlation with different populations of nearby extragalactic objects: galaxies in the 2MRS catalog, AGNs detected by Swift-BAT, radio galaxies with jets and the Centaurus A galaxy. None of the tests shows a statistically significant evidence of anisotropy. The strongest departures from isotropy (post-trial probability ∼1.4%) are obtained for cosmic rays with E > 58 EeV in rather large windows around Swift AGNs closer than 130 Mpc and -6brighter than 10 44 erg/s (18 • radius) and around the direction of Centaurus A (15 • radius).

Propagation of ultrahigh energy cosmic rays in extragalactic magnetic fields: a view from cosmological simulations

“…The left panel of this Figure can be compared to Fig. 10 of Aab et al (2015) which shows the distribution of separation angles from Cen A. The isotropic prediction is the same as in Fig.…”

A Novel Study Connecting Ultra-High Energy Cosmic Rays, Neutrinos, and Gamma-Rays

“…Moreover, it is difficult to quote a UHECR horizon a priori. Instead of scanning in redshift z as done in other tests [14,15], we use all sources regardless of their redshift. As done in [29], we have selected γ-ray sources in spatial coincidence with the neutrinos (i.e.…”

“…The former has detected 231 such events covering mostly the southern hemisphere and the latter 72 events above 57×10 18 eV covering mostly the northern sky. Despite a series of studies on the UHECR arrival direction distributions [14,15], no counterparts have yet been determined. The strongest deviations from isotropy (post-trial p-values ∼ 1.3 − 1.4%) have been obtained for E ≥ 58 × 10 18 eV in connection with Swift AGN closer than 130 Mpc and more luminous than 10 44 erg s −1 , and around the direction of Cen A (at angular separations ∼ 18 • and ∼ 15 • respectively) [14].…”

“…However, two "hot" regions (2−3σ deviations) of about 20 • in the cosmic ray sky have been reported (see Fig. 1 left and [14,16]) but their interpretation is not yet clear.…”

The Pierre Auger Observatory status and latest results

“…The presence of anisotropies is searched for at small and intermediate angular scales [16] in the distribution of arrival directions of the most energetic cosmic rays above a few tens of EeV, where the magnetic deflections (at least of those with a small charge) may be only a few degrees. Different methods are employed: search for autocorrelation by looking for pairs of events, blind search for localized excesses of events (Fig.…”