Fermi-LAT gamma-ray signal from Earth Limb, systematic detector effects
  and their implications for the 130 GeV gamma-ray excess
  We look for possible spectral features and systematic effects in Fermi-LAT
publicly available high-energy gamma-ray data by studying photons from the
Galactic centre, nearby galaxy clusters, nearby brightest galaxies, AGNs,
unassociated sources, hydrogen clouds and Earth Limb. Apart from already known
130 GeV gamma-ray excesses from the first two sources, we find no new
statistically significant signal from others. Much of our effort goes to
studying Earth Limb photons. In the energy range 30 GeV to 200 GeV the Earth
Limb gamma-ray spectrum follows power-law with spectral index 2.87\pm 0.04 at
95 % CL, in a good agreement with the PAMELA measurement of cosmic ray proton
spectral index between 2.82-2.85, confirming the physical origin of the Limb
gamma-rays. In small subsets of Earth Limb data with small photon incidence
angle it is possible to obtain spectral features at different energies,
including at 130 GeV, but determination of background, thus their
significances, has large uncertainties in those cases. We observe systematic
2\sigma level differences in the Earth Limb spectra of gamma-rays with small
and large incidence angles. The behaviour of those spectral features as well as
background indicates that they are likely statistical fluctuations.
