  Lower limits on the energy cutoff for unidentified gamma-ray sources detected
in the HESS galactic plane survey are derived. Additional public data from the
VERITAS, HESS and Milagro experiments are used for MGRO J1908+06 to confirm the
limit derived from the HESS galactic plane survey data and to enable further
conclusions on the presence of spectral breaks. Five Pevatron candidates are
identified in the HESS galactic plane survey. The cutoff of the gamma-ray
spectrum for these sources is larger than 20 TeV at 90% confidence level. The
gamma-ray sources MGRO J1908+06 and HESS J1641-463, found to be Pevatron
candidates in the analysis of the HESS galactic plane survey catalog, had been
discussed as Pevatron candidates before. For MGRO J1908+06, the lower limit on
the gamma-ray energy cutoff is 30 TeV at 90% confidence level. This is a factor
of almost two larger than previous results. Additionally, a break in the
gamma-ray spectrum at energies between 1 TeV and 10 TeV with an index change
larger than 0.5 can be excluded at 90% confidence level for MGRO J1908+06. The
energy cutoff of accelerated particles is larger than 100 TeV at 90% confidence
level in a hadronic scenario for all five Pevatron candidates. A hadronic
scenario is plausible for at least three of the Pevatron candidates, based on
the presence of nearby molecular clouds and supernova remnants.
