The coexistence of powerful accelerators of cosmic rays with intense background radiation fields creates unique conditions, where the Ultra-High-Energy Cosmic Rays (UHECRs) interactions could take place copiously and produce several secondary particles.
In particular, such phenomena could explain the features observed in the UHECR spectrum measurements.
This scenario is explored extending SimProp, a simulation code for UHECR extra-galactic propagation, allowing us to compute the interactions inside and outside the source.
Inspired by recent results from the Pierre Auger Observatory on the anisotropy in the arrival directions of the highest energy cosmic-rays, the simulations are performed in the context of Starburst Galaxies, one of the most promising candidate sources.
We model the interactive and diffusive processes in the region surrounding the Starburst Nucleus, taking into account interactions with background photons and the interstellar medium. The escaping cosmic-ray flux is then propagated to the Earth and compared with the experimental spectrum and composition measured by the Pierre Auger Observatory.
The proposed method could be used to connect the features of the UHECR spectrum and composition at Earth to the parameters describing Starburst Galaxies.
In addition, neutrinos directly produced in these sources can be compared to the measured IceCube flux, thus providing an additional way to constrain some source parameters.