  Results of a search for new phenomena in events with an energetic photon and
large missing transverse momentum with the ATLAS experiment at the LHC are
reported. Data were collected in proton--proton collisions at a center-of-mass
energy of 8 TeV and correspond to an integrated luminosity of 20.3 fb$^{-1}$.
The observed data are well described by the expected Standard Model
backgrounds. The expected (observed) upper limit on the fiducial cross section
for the production of such events is 6.1 (5.3) fb at 95% confidence level.
Exclusion limits are presented on models of new phenomena with large extra
spatial dimensions, supersymmetric quarks, and direct pair production of
dark-matter candidates.
