We propose to develop a new analysis approach for charged particle astronomy to find the astrophysical sources of cosmic particles with extreme energies. During the recent years, there has been a rapid progress in our understanding of Galactic magnetic field (GMF) and the collected statistics of ultra-high energy cosmic ray events. It should therefore be possible to correct the measured arrival directions of cosmic rays on Earth for deflections in the GMF and to significantly improve the search for their astrophysical sources in this way. The research objectives of this proposal are therefore: 1) A thorough evaluation of the uncertainties of the GMF with the aim of producing sky maps of the deflection uncertainty of cosmic rays given their arrival direction and rigidity (= energy divided by charge). 2) Development of an optimal analysis method for correlation studies that takes into account the deflection uncertainties originating from the uncertainties in both, GMF and the estimated rigidities. 3) Application of the optimal data analysis method to data of the Pierre Auger Observatory. During the outgoing phase, the fellow will join the astrophysics group of the New York University to acquire state-of-the art knowledge on the interpretation of astrophysical data relevant for the GMF. At the return host, the Karlsruher Institute of Technology, he will apply the obtained knowledge to data of the Pierre Auger Observatory. This project will allow the fellow to be trained in the theoretical foundations and computational tools needed to study the GMF. It will broaden his knowledge in astrophysics and therefore complement his current expertise of the particle physics of air showers. The interdisciplinary training and the possibility to gain teaching experience at both hosts, will contribute to the long-term development of the fellow’s career and make him eligible for a leading academic position in Europe.