UHECRs: a CRISP image of the origins

In the ultra-high-energy range, cosmic rays (UHECRs) can originate from distances as large as a few hundreds of megaparsecs, limited mainly by interactions with the infrared background light and the cosmic microwave background. Although a modest size, such volume may contain too many sources to be able to discern the origin with the capabilities of current observatories. Furthermore, the deflections caused by extragalactic magnetic fields (EGMFs) may further blur the arrival directions after some propagation distance. However, cosmic rays of extreme energies (ExECRs) may have much shorter disintegration lengths (depending on the mass) and thus are a strong indication of nearby sources in the range of a few tens of megaparsecs. We establish a neighboring volume with the largest potential for the discovery of UHECR sources based on the observational constraints and the observed ExECRs. The radial constraints are defined by the nuclear species observed at Earth and the composition evolution. Well defined distances are achieved with the package CRISP that computes the probability distributions describing the nuclear disintegrations caused by interactions during propagation. The angular constraints are established by models of the galactic magnetic field and the observed composition. The robustness of the results is estimated by determining the impact of factors like the photonuclear cross sections and the EGMF properties. The required specifications for observatories of ExECRs are provided.