Evidence for a connection between the gamma-ray and the highest energy   cosmic-ray emissions by BL Lacertae objects
  A set of potentially gamma-ray--loud BL Lac objects is selected by intersecting the EGRET and BL Lac catalogs. Of the resulting 14 objects, eight are found to correlate with arrival directions of ultra--high-energy cosmic rays (UHECRs), with significance of the order of 5 sigma. This suggests that gamma-ray emission can be used as a distinctive feature of those BL Lac objects that are capable of producing UHECR. 
D. Gorbunov, P. Tinyakov, I. Tkachev and S. Troitsky