Lower Limits on the Anisotropy of the Extragalactic Gamma-Ray Background
  implied by the 2FGL and 1FHL Catalogs
  In principle, the angular anisotropy in the extragalactic gamma-ray
background (EGRB) places severe constraints upon putative populations of
unresolved gamma-ray point sources. Existing estimates of the EGRB anisotropy
have been constructed by excising known point sources, e.g., taken from the
First or 2 Year Fermi-LAT Source Catalog (1FGL or 2FGL, respectively) and
statistically analyzing the residual gamma-ray sky maps. We perform an
independent check of the EGRB anisotropy limits by comparing the values
obtained from the 1FGL-masked sky maps to the signal implied by sources that
lie below the 1FGL detection threshold in the more sensitive 2FGL and 1FHL
(First Fermi-LAT catalog of >10 GeV sources). As such, our analysis provides an
internal consistency check of implications for source counts and spectral index
distributions of gamma-ray bright active galactic nuclei obtained from
Fermi-LAT data. Based on this, we find evidence for substantially larger
anisotropies than those previously reported at energies above 5 GeV, where BL
Lac objects are likely to provide the bulk of their contribution to the EGRB.
This uncertainty in the EGRB anisotropy cautions against using it as an
independent constraint for the high-redshift gamma-ray universe. Moreover, this
would suggest that contrary to previous claims, smooth extensions of the
resolved point-source population may be able to simultaneously explain both the
isotropic and anisotropic components of the EGRB.
