It has already been pointed out that the EGRB should break above ~ 20 GeV
energy owing to absorption of high energy
-rays by pair-production
interactions with lower energy starlight photons
[16].
There is also another potential cause for a steepening in the EGRB
from blazars. The EGRET detector obtained rough power-law spectral
indeces for blazars in the 0.1 to 10 GeV energy decade, however, we
presently have no data for these objects in the 10 to 100 GeV decade.
Presently popular theoretical models
predict that the spectra of highly luminous blazars will exhibit a cutoff at
energies in the 10 to 100 GeV range, whereas the less luminous X-ray
selected
BL Lac objects can have spectra extending into the TeV energy range
[27],
[28].
Indeed, there have now been ground based detections of at least 5 X-ray
selected BL Lac objects (Weekes, these proceedings),
some of whose spectra extend to multi-TeV energies. While no other types of
blazars have been seen at TeV energies, this may be an result of
intergalactic
-ray absorption
[16],
[29],
[30] so that we
do not really know if
their intrinsic spectra turn down at energies in the 10 to 100 GeV decade.
The GLAST telescope should provide this knowledge in the
not-too-distant future.
If the spectra of most blazars possess intrinsic cutoffs above 10 GeV, then the EGRB from unresolved blazars would be expected to turn over as well. This effect should be more dramatic than the steepening in the EGRB predicted from the effect of intergalactic absorption [16]. In that case, if the EGRET results on the EGRB up to 100 GeV are correct, a new component may be present in this higher energy range. Such a component has been predicted to be produced by the decay of ~ TeV mass higgs bosons from cosmic string processes in flat-potential supersymmetric models [31]. Of course, there may be other unknown possibilities as well.