Prospect on intergalactic magnetic field measurements with gamma-ray instruments

SOL Helene, helene.sol@obspm.fr, CNRS, Paris Observatory, France
ZECH Andreas, Paris Observatory
BOISSON Catherine, Paris Observatory
KRAWCZYNSKI Henric, Washington Univ. in St Louis
FALLON Lisa, DIAS
de GOUVEIA Dal PINO Elisabete, Univ. of Sao Paulo
HINTON Jim, Univ. of Leicester
INOUE Susumu, Univ. of Tokyo
NERONOV, Andrii ISDC
WHITE Richard, Univ. of Leicester

Abstract
Observing high-energy gamma-rays from Active Galactic Nuclei offers a unique potential to probe extremely tiny values of the intergalactic magnetic field (IGMF), a long standing question of astrophysics, astroparticle physics and cosmology. Very high energy (VHE) photons from blazars propagating along the line of sight interact with the extragalactic background light (EBL) and produce e+e- pairs. Through inverse-Compton emission, these pairs generate secondary GeV-TeV components accompanying the primary VHE signal. Such secondary components could be detected in the gamma-ray range as delayed “pair echos” for very weak IGMF (B < 10-16 G), while they should result in a spatially extended gamma-ray emission around the source for higher IGMF values (B > 10-16 G). Coordinated observations with space (i.e. Fermi) and ground-based gamma-ray projects, such as the current Cherenkov experiments HESS, MAGIC and VERITAS, the future Cherenkov Telescope Array (CTA) Observatory, and the wide-field instruments such as HAWC and LHAASO, should allow to analyze and finally detect such echos, extended emission or pair halos, and to further characterize the IGMF.