Tracing protons through the Galactic magnetic field: a clue for charge composition of ultra-high energy cosmic rays

We reconstruct the trajectories of ultra-high energy cosmic rays (UHECR) - observed by the AGASA experiment - in the Galactic magnetic field assuming that all particles have the same charge. We then study correlations between the reconstructed events and BL Lacs. The correlations have significance below 10^{-3} in the case of particles with charge +1. In the case of charge -1 the correlations are absent. We interpret this as evidence that protons are present in the flux of UHECR. Observed correlation provides an independent evidence that BL Lacs emit UHECR.