An upper limit on the strength of the extragalactic magnetic field from ultra-high-energy cosmic-ray anisotropy

Understand

If ultra-high-energy cosmic rays originate from extragalactic sources, the offsets of their arrival directions from these sources imply an upper limit on the strength of the extragalactic magnetic field.

• The Pierre Auger Collaboration has recently reported that anisotropy in the arrival directions of cosmic rays is correlated with several types of extragalactic objects.
• If these cosmic rays originate from these objects, they imply a limit on the extragalactic magnetic field strength of B < 0.7-2.2 x 10^-9 (lambda_B / 1 Mpc)^-1/2 G for coherence lengths lambda_B < 100 Mpc and B < 0.7-2.2 x 10^-10 G at larger scales.
• This is comparable to existing upper limits at lambda_B = 1 Mpc, and improves on them by a factor 4-12 at larger scales.