Gamma-ray induced air showers are notable for their lack of muons, compared
to hadronic showers. Hence, air shower arrays with large underground muon
detectors can select a sample greatly enriched in photon showers by rejecting
showers containing muons. IceCube is sensitive to muons with energies above
~500 GeV at the surface, which provides an efficient veto system for hadronic
air showers with energies above 1 PeV. One year of data from the 40-string
IceCube configuration was used to perform a search for point sources and a
Galactic diffuse signal. No sources were found, resulting in a 90% C.L. upper
limit on the ratio of gamma rays to cosmic rays of 1.2 x 10^(-3)for the flux
coming from the Galactic Plane region (-80 deg < l < -30 deg; -10 deg < b < 5
deg) in the energy range 1.2 - 6.0 PeV. In the same energy range, point source
fluxes with E^(-2) spectra have been excluded at a level of (E/TeV)^2 d\Phi/dE
~ 10^(-12)-10^(-11) cm^2/s/TeV depending on source declination. The complete
IceCube detector will have a better sensitivity, due to the larger detector
size, improved reconstruction and vetoing techniques. Preliminary data from the
nearly-final IceCube detector configuration has been used to estimate the 5
year sensitivity of the full detector. It is found to be more than an order of
magnitude better, allowing the search for PeV extensions of known TeV gamma-ray
emitters.
