several tenths of a micro Gauss, but elsewhere they should be much weaker (e.g., Kronberg 2001). The gyroradius can be written conveniently as $r_g \approx E_{ZeV}/(Z B_{nG})$ Gpc, where B is now expressed in nano Gauss. Except in clusters or possibly the vicinity of galaxies the expected deflections should be small over distances that hadronic CRs can propagate without severe energy losses. Therefore most UHECR explanations anticipate that detected events point back to the original sources, which must then be relatively isotropic. Some analyses have suggested enhancements in the UHECR distribution towards “interesting” regions of the sky, particularly the super galactic plane, but at present the evidence does not seem to support any such biases (e.g., Takeda, 1999; Uchihori, 2000).

The possibility that particle trajectories are significantly deflected is still an open question, however (e.g., Medina-Tanco, 1997; Lemoine, 1997; Biermann, 2001; Medina-Tanco & En$\ss$lin 2001). Biermann, 2001, for example, have argued that a wind from our galaxy could carry a strong enough magnetic field to sufficient distance that UHECR trajectories would be strongly modified. They have shown that such a field might redistribute the 13 highest energy events detected at that time in a way consistent with their common origin 