Extreme TeV blazars and the intergalactic magnetic field
  We study the four BL Lac objects (RGB J0152+017, 1ES 0229+200, 1ES 0347-121
and PKS 0548-322) detected in the TeV band but not present in the 1FGL
catalogue of the Fermi/Large Area Telescope. We analize the 24 months of LAT
data deriving gamma-ray fluxes or upper limits that we use to assemble their
spectral energy distributions (SED). We model the SEDs with a standard one-zone
leptonic model, also including the contribution of the reprocessed radiation in
the multi GeV band, emitted by the pairs produced through the conversion of the
primary TeV emission by interaction with the cosmic optical-IR background. For
simplicity, in the calculation of this component we adopt an analytical
approach including some simplifying assumptions, in particular i) the blazar
high energy emission is considered on average stable over times of the order of
10^7 years and ii) the observer is exactly on-axis. We compare the physical
parameters derived by the emission model with those of other high-energy
emitting BL Lacs, confirming that TeV BL Lacs with a rather small GeV flux are
characterized by extremely low values of the magnetic field and large values of
the electron energies. The comparison between the flux in the GeV band and that
expected from the reprocessed TeV emission allows us to confirm and strengthen
the lower limit of B >10^{-15} G for the intergalactic magnetic field using a
theoretically motivated spectrum for the primary high-energy photons.
