Lower bound on the local extragalactic magnetic field

Assuming that the hard γ-ray emission of Cen A is a result of synchrotron radiation of ultrarelativistic electrons, we derive a lower bound on the local extragalactic magnetic field, $B>\mathrm{}{10}^{-8}\hspace{0.5em}\mathrm{G}.$ 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.