Source position reconstruction and constraints on the galactic magnetic
  field from ultra-high energy cosmic rays
  We study the possibility to reconstruct the position of ultra-high energy
cosmic ray sources and some properties of the magnetic field along the line of
sight towards them in the case that several events from the same source are
detected. By considering an illustrative model for the galactic magnetic field,
including both a regular and a turbulent component, we estimate the accuracy
that can be achieved in the reconstruction. We analyse the effect of the
experimental energy and angular resolutions on these results. We show that if
about ten events with energies above 30 EeV are detected coming from the same
source, it should be possible to reconstruct the source position with an
accuracy of 0.5$^{\circ}$ and the integral of the orthogonal component of the
magnetic field along the line of sight with an accuracy of 0.6 $\mu$G kpc
Z$^{-1}$ (with Z the electric charge of the particles).
