Large-scale, intergalactic magnetic and radiation fields (invited talk)

Abstract

I review the recent evidence for existence of large scale intergalactic magnetic fields (IGMF) derived from the gamma-ray observations of distant TeV gamma-ray loud blazars. Non-observation of the signal from electromagnetic cascade initiated by TeV gamma-rays in the intergalactic medium imposes a lower bound on IGMF strength at the level of B > 10−17 G if the IGMF correlation length is larger than ∼ 1 Mpc and the cascade signal is assumed to be suppressed due to the time delay of the cascade emission. The bound is B > 10−16 G for Mpc-scale correlation lenght if the cascade emission is not observed due to the extended nature of the cascade emission. The bound improves as λ−1/2 if magnetic field correlation length is much smaller than a Mega-parsec. This lower bound constrains models for the origin of cosmic magnetic fields.