Intergalactic magnetic field lower limits up to the redshift $z\approx3$

Ievgen Vovk

Paper

Intergalactic magnetic field lower limits up to the redshift $z\approx3$

Abstract

Large-scale intergalactic magnetic fields may contain a mixture of galactic and cosmogenic contributions, that can be probed via observations of

-ray "echo" from sources at cosmological distances. While these contributions may be disentangled based on the difference in their redshift evolution, thus far indications of non-negligible magnetic field have been found only at low redshifts. This work aims at extending the intergalactic magnetic field constraints to redshifts

using 17-year long all-sky observations of high-redshift active galactic nuclei with Fermi/LAT

-ray telescope. Combing the Fermi/LAT measurements in the 0.1 GeV - 1 TeV energy range with the Monte Carlo simulations of the

-ray "echo", it is shown that the zero field strength hypothesis at

is disfavoured at the

significance level, yielding the lower limit of

cG for the magnetic field correlation length above 1 Mpc. It is further shown that the same data put a lower limit on the volume-filling fraction of this field of

in the redshift range considered. It is also demonstrated that the derived limits are not substantially affected by either source flux variability or the assumed

-ray emission attenuation model. Implications of these limits for intergalactic magnetic field origin are discussed.