ИСТИНА

Extragalactic magnetic fields remain extremely elusive. Non-observation of cascade gamma-rays from VHE sources imply that there is a lower bound on their strength Bmin∼10^−17 G. The upper bound could be larger than 10^−8 G. Magnetic fields of such strength could considerably alter the process of UHECR propagation, increasing deflection of proton UHECRs and even introducing so-called 'magnetic horizons' for heavier nuclei. In this work we have used rotation measures of the sources with known redshift from the NVSS catalogue. Redshift evolution of their intrinsic RMs could have been caused by extragalactic fields. Absence of any clear-cut evolution thus allowed us to constrain strength of the extragalactic magnetic fields at several nGs.