About the project

Cosmic rays (CRs) are extremely energetic and mostly charged particles of cosmic origin. The identity of the CR sources are to date not known. A dedicated method is developed in this project with thegoal to contribute to the identification of the sources of the ultra-high energy (UHE, ≥ at least several EeV) cosmic rays. Actually, the highest energetic particles can reach energies comparable to a tennis ball flying with almost 100 km/h.

Recent results from UHECR measurements favor conventional scenarios of UHECR production at astrophysical sites. Meaning, particles are rather accelerated to these energies than produced by the decay of exotic particles. Prominent jet outflows in powerful active Galactic Nuclei (AGN) provide suitable conditions and energetics for charged particle acceleration up to the highest energies, and are therefore considered prime contributors to the observed UHECR flux. During the acceleration of the CRs in so-called "hadronic interactions" photons and neutrinos are produced. As charge-neutral messengers they provide information about CR source direction on the sky, and the physical conditions at the CR production site, while the charged CRs suffer from loss of directional information by deflecting at cosmic magnetic fields. To gain insights into the identity of the UHECR sources and the dominating acceleration and emission mechanisms at source we therefore employ a multi-messenger, multi-wavelength approach including Pierre Auger Observatory measured UHECR events, high- (HE, ≥ 100 MeV) and very-high energy (VHE, ≥ 30 GeV) gamma-ray emission collected by the Fermi-LAT detector and ground-based Cherenkov telescopes, and VHE neutrinos observed with the IceCube experiment.

In the proposed multistep procedure first all nearby AGN are classified according to their capability to accelerate particles to UHEs. For this purpose we use multi-frequency measurements of them complemented with energetics arguments to build a list of suitable nearby UHECR AGN candidates. Auger data point to heavy mass nuclei composition at extreme energies. Therefore current state-of-the art AGN emission models will be extended (by the Austrian team members) to allow the treatment of heavy nuclei. Subsequent simulations of possible UHECR arrival directions, given this candidate list, for various cosmic magnetic field configurations using a propagation code (adapted by the Slovenian project partners) will predict the UHECR patterns observed at Earth, to be cross-correlated with Auger data. In a complementary approach the expected signatures of the produced photon and neutrino emission are analyzed in conjunction with LAT- and neutrino data. The results of this study are finally fed into predictions of characteristic features that signal UHECRs in AGN jets and that is verifiable by the near-future Cherenkov Telescope Array (CTA). We are supported by the participation of numerous world leading scientists from Italy and Poland.

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