GRB 831221 , the SIMBAD biblio

We investigate the origin of a nearly pointlike cluster of five ultra-high-energy cosmic rays (UHECRs) in the vicinity of R.A.~169°.2 and decl.~56°.8, using Sloan Digital Sky Survey and other data. No particular source candidates are found near the estimated source direction, but the direction is exceptional in having a likely merging pair of galaxy clusters at 140 h^–1 Mpc, with an unusually low foreground density. Large-scale shocks or another product of the merging galaxy clusters may accelerate the UHECRs, or the merging galaxy clusters may be coincidental and the UHECRs may be accelerated in a rare event of an unexceptional progenitor. Low magnetic deflections in the foreground void may explain why this is the only identified pointlike cluster of so many UHECRs.