Final Report Summary - HE-COSMIC-SOURCES (Probing the relativistic jet composition in high energy active galactic nuclei) Executive Summary:The overall scientific objectives of this project aimed towards probing the relativistic particle content in jets of active galactic nuclei (AGN), the most numerous, persistent population of high energy cosmic sources in the Universe. Such powerful objects are among the prime candidate sources of the enigmatic ultrahigh energy cosmic rays, however, conclusive evidence is still missing. A required tool for this undertaking, a self-consistent time-dependent high energy radiation transport code that takes into account leptonic and hadronic processes in relativistic magnetized jet environments, has been developed. The simulation of light curves has revealed that an observational fingerprint of hadronic interactions in photon data is unlikely to be identified with temporal data only. Spectral data are essential. The scientific project objectives are leveraged by today's synergy of the high performance ground- (i.e. modern Cherenkov telescopes, radio and optical telescopes around the world) and the space-based photon detecting instrument LAT onboard the Fermi satellite yielding dense high quality data over a broad energy range from a large collection of AGN. A data base of simultaneous broadband spectral observations of the most suitable AGN for this project has been accumulated. The modeling of all sources in this data base seem to indicate that rather hard VHE gamma ray spectra can be more naturally explained by hadronic rather than leptonic interactions, and can therefore serve as an interesting diagnostic feature to search for hadronic interactions in photon data from AGN jets. This is particular interesting for future gamma-ray observatories such as the Cherenkov Telescope Array (CTA). Neutrinos from AGN jets constitute a clear fingerprint of hadronic interactions therein. The expected neutrino flux from all sources in the data base has been calculated putting further interesting constraints on the parameter space (e.g. the composition of the material in AGN jets) of hadronic models.Project webpage:http://homepage.uibk.ac.at/~c705282/This grant has contributed to promote the professional reintegration of the proposer working in theoretical astroparticle/high energy astrophysics into the European astroparticle physics community and complements the activities of the experimental astroparticle physics group at the University of Innsbruck. More importantly, it helped implementing a lasting professional integration of the proposer at the University of Innsbruck, and a continuing research career in Europe.