  High-energy gamma-rays propagating in the intergalactic medium can interact
with background infrared photons to produce e+e- pairs, resulting in the
absorption of the intrinsic gamma-ray spectrum. TeV observations of the distant
blazar 1ES 1101-232 were thus recently used to put an upper limit on the
infrared extragalactic background light density. The created pairs can
upscatter background photons to high energies, which in turn may pair produce,
thereby initiating a cascade. The pairs diffuse on the extragalactic magnetic
field (EMF) and cascade emission has been suggested as a means for measuring
its intensity. Limits on the IR background and EMF are reconsidered taking into
account cascade emissions. The cascade equations are solved numerically.
Assuming a power-law intrinsic spectrum, the observed 100 MeV - 100 TeV
spectrum is found as a function of the intrinsic spectral index and the
intensity of the EMF. Cascades emit mainly at or below 100 GeV. The observed
TeV spectrum appears softer than for pure absorption when cascade emission is
taken into account. The upper limit on the IR photon background is found to be
robust. Inversely, the intrinsic spectra needed to fit the TeV data are
uncomfortably hard when cascade emission makes a significant contribution to
the observed spectrum. An EMF intensity around 1e-8 nG leads to a
characteristic spectral hump in the GLAST band. Higher EMF intensities divert
the pairs away from the line-of-sight and the cascade contribution to the
spectrum becomes negligible.
