Search for Extended {\gamma}-ray Emission around AGN with H.E.S.S. and
  Fermi-LAT
  Context: Very-high-energy (VHE; E>100 GeV) {\gamma}-ray emission from blazars
inevitably gives rise to electron-positron pair production through the
interaction of these {\gamma}-rays with the Extragalactic Background Light
(EBL). Depending on the magnetic fields in the proximity of the source, the
cascade initiated from pair production can result in either an isotropic halo
around an initially beamed source or a magnetically broadened cascade flux.
Aims: Both extended pair halo (PH) and magnetically broadened cascade (MBC)
emission from regions surrounding the blazars 1ES 1101-232, 1ES 0229+200 and
PKS 2155-304 were searched for, using VHE {\gamma}-ray data taken with the High
Energy Stereoscopic System (H.E.S.S.), and high energy (HE; 100 MeV<E<100 GeV)
{\gamma}-ray data with the Fermi Large Area Telescope (LAT). Methods: By
comparing the angular distributions of the reconstructed gamma-ray events to
the angular profiles calculated from detailed theoretical models, the presence
of PH and MBC was investigated. Results: Upper limits on the extended emission
around 1ES 1101-232, 1ES 0229+200 and PKS 2155-304 are found to be at a level
of few percent of the Crab nebula flux above 1 TeV, depending on the assumed
photon index of the cascade emission. Assuming strong Extra-Galactic Magnetic
Field (EGMF) values, > 10$^{-12}$G, this limits the production of pair halos
developing from electromagnetic cascades. For weaker magnetic fields, in which
electromagnetic cascades would result in magnetically broadened cascades, EGMF
strengths in the range (0.3 - 3)$\times 10^{-15}$G were excluded for PKS
2155-304 at the 99% confidence level, under the assumption of a 1 Mpc coherence
length.
