On the Luminosity of the Ultra High Energy Cosmic Rays Sources

The energy density of the Ultra High Energy Cosmic Rays (UHECR) in the Universe is a very important parameter for the solution of the puzzle of their origin. It defines the luminosity of the UHECR sources and thus the type of objects they are. This is also of crucial importance for the design of high energy neutrino telescopes. The current attempts to derive the source luminosity are hindered by the small world experimental statistics. We show that the unknown strength and structure of the large scale cosmic magnetic fields affect strongly the UHECR propagation history. The identification of the UHECR sources will bring important information on the large scale magnetic fields.