A lower bound on the local extragalactic magnetic field

Abstract

Assuming that the hard gamma-ray emission of Cen A is a result of synchrotron radiation of ultra-relativistic electrons, we derive a lower bound on the local extragalactic magnetic field, $B>10^{-8}$ G. This result is consistent with (and close to) upper bounds on magnetic fields derived from consideration of cosmic microwave background distortions and Faraday rotation measurements.

Comments: Includes extensive discussion of particle acceleration above 10^20 eV in the hot spot-like region of Cen A