Implications of gamma-ray and neutrino observations on source models of ultrahigh energy cosmic rays

A.D. SUPANITSKY

Foz do Iguaçu

Conferencia; Black Holes as Cosmic Batteries: UHECRs and Multimessenger Astronomy; 2019

The origin and nature of the ultrahigh energy cosmic rays (UHECRs) are still unknown. However, great progress has been achieved in past years due to the observations performed by the Pierre Auger Observatory and Telescope Array. Above 10^18 eV the observed energy spectrum presents two features: a hardening of the slope at about 10^18.7 eV, which is known as the ankle and a suppression at approximately 10^19.6 eV. The composition inferred from the experimental data, interpreted by using the current high energy hadronic interaction models, seems to be lightbelow the ankle, showing a trend to heavier nuclei for increasing values of the primary energy. Current high energy hadronic interaction models, updated by using Large Hadron Collider data, are still subject to large systematic uncertainties, which makes difficult the interpretation of theexperimental data in terms of composition. On the other hand, it is very well known that gamma rays and neutrinos are produced by UHECRs during propagation from their sources, as a consequence of their interactions with the radiation field present in the universe. The flux at Earth of these secondary particles depends on the source models of UHECRs including the chemical composition at injection. Therefore, both gamma-ray and neutrino observations can be used to constrain source models of UHECRs, including the composition in a way which is independent of the high energy hadronic interaction models. In this article I will review recent results obtained by using the latest gamma-ray and neutrino observations.