  As very high energy (~100 GeV) gamma rays travel over cosmological distances,
their flux is attenuated through interactions with the extragalactic background
light. Observations of distant gamma ray sources at energies between ~200 GeV
and a few TeV by ground-based gamma ray telescopes such as HESS, however,
suggest that the universe is more transparent to very high energy photons than
had been anticipated. One possible explanation for this is the existence of
axion-like-particles (ALPs) which gamma rays can efficiently oscillate into,
enabling them to travel cosmological distances without attenuation. In this
article, we use data from the Fermi Gamma Ray Space Telescope to calculate the
spectra at 1-100 GeV of two gamma ray sources, 1ES1101-232 at redshift z=0.186
and H2356-309 at z=0.165, and use this in conjunction with the measurements of
ground-based telescopes to test the ALP hypothesis. We find that the
observations can be well-fit by an intrinsic power-law source spectrum with
indices of -1.72 and -2.1 for 1ES1101-232 and H2356-309, respectively, and that
no ALPs or other exotic physics is necessary to explain the observed degree of
attenuation.
