Isotropization of ultra-high energy cosmic ray arrival directions by radioghosts

The isotropy in the ultra-high energy cosmic ray (UHECR) flux observed by Y akutsk and AGASA experiments, is a very strong constraint to production and propagation models alike. Most of the scenarios proposed in the literature should produce a sizable anisotropy as either extragalactic luminous or da rk matter is normally associated with the invoked particle sources. We expl ore the possibility that the magnetic fields in fossil cocoons of former ra dio galaxies so called radio ghosts [En beta lin, Ringberg Workshop on 'Dif fuse Thermal and Relativistic Plasma in Galaxy Clusters', vol. 271, MPE Rep ort, 1999, p. 275] - are able to scatter UHECR in the intergalactic medium giving rise to the observed isotropy. We show, through numerical simulation s, under which conditions this process can be operative and the magnitude o f the effect. We further demonstrate, that if radio ghosts mix with the amb ient medium, they might be able to produce the observed magnetic fields in clusters of galaxies. In the case of mixing, the UHECR isotropization would be even stronger than in our conservative estimates. (C) 2001 Elsevier Sci ence B.V. All rights reserved.