Signatures of galactic magnetic lensing upon ultra high energy cosmic rays

We analyse several implications of lensing by the regular component of thegalactic magnetic field upon the observed properties of ultra high energycosmic rays. Magnetic fields deflect cosmic ray trajectories, causing flux(de)magnification, formation of multiple images of a single source, and timedelays. We derive the energy dependence of these effects near the caustics atwhich the flux amplification of a point source diverges. We show that the largemagnification of images around caustics leads to an amplification bias, whichcan make them dominate the flux in some energy ranges. We argue that clusteringin the arrival directions of UHECRs of comparable energy may be due to magneticlensing around caustics. We show that magnetic lensing can also significantlyalter the observed composition of cosmic rays at the highest energies. We alsoshow that the time delay between events from a single image may monotonicallydecrease with decreasing energy in the neighborhood of a caustic, opposite toits behaviour in normal regions.Comment: 18 pages, 7 figures, uses JHEP.cl