Abstract

Context. The origin and composition of ultra-high energy cosmic rays (UHECRs) remain unclear. Possible sources include active galactic nuclei - selected by various criteria - and extragalactic magnetars. Aims. We aim to improve constraints on the source population(s) and compositions of UHECRs by accounting for UHECR deflections within existing Galactic magnetic field models (GMFs). Methods. We used Monte Carlo simulations for UHECRs detected by the Pierre Auger Observatory and AGASA, to determine the UHECR trajectories within the Galaxy and their outside-the-Galaxy arrival directions. The simulations, which used UHECR compositions from protons to iron and seven models of the ordered GMF, accounted for uncertainties in the GMF and a turbulent magnetic field component. Trajectories and outside-the-Galaxy arrival directions were compared with Galactic and extragalactic sources. Results. For a given proton or light UHECR, the multiple potential outside-the-Galaxy arrival directions within a given GMF model are not very different, allowing meaningful constraints on source populations. Our previous claim of a correlation between a subset of UHECRs and nearby extended radiogalaxies remains valid, even strengthened, within several GMF models. Both the nearest radiogalaxy Cen A, and the nearest radio-extended BL Lac, CGCG 413-019, are potential sources of multiple UHECRs. The correlation appears to be linked to the extended radio source rather than a tracer of an underlying matter distribution. Several UHECRs have trajectories that pass close to the Galactic plane, some passing close to Galactic magnetars and/or microquasars. For heavier UHECRs, the multiple potential outside-the-Galaxy arrival directions of any given UHECR are highly scattered but still allow meaningful constraints. It is possible, but unlikely, that all UHECRs originate in the nearby radiogalaxy Cen A. Conclusions. Nearby radiogalaxies remain a strong potential source of a significant subset of UHECRs. For light UHECRs, about a third of UHECRs can be "matched" to nearby galaxies with extended radio jets. The remaining UHECRs could also be explained as originating in extended radiogalaxies if one has at least one of: a large UHECR mean free path, a high cluster and/or intergalactic magnetic field, and a heavy composition for two-thirds of the detected UHECRs. If extended radiogalaxies are, or trace, UHECR sources, the most consistent models for the ordered GMF are the BS-S and BS-A models; the GMF models of Sun and collaborators are acceptable if a dipole component is added. © 2010 ESO.