  The supernova remnant Kes 73 and/or the magnetar 1E 1841-045 at its center
can deposit a large amount of energy to the surroundings and is potentially
responsible for particle acceleration. Using the data taken with the Fermi
Large Area Telescope (LAT), we confirmed the presence of an extended source
whose centroid position is highly consistent with this
magnetar/supernova-remnant pair. Its emission is intense from 100 MeV to $>$100
GeV. Its LAT spectrum can be decoupled into two components which are
respectively governed by two different mechanisms. According to the young age
of this system, the magnetar is seemingly a necessary and sufficient source for
the downward-curved spectrum below 10 GeV, as the observed $<$10 GeV flux is
too high for the supernova remnant to account for. On the other hand, the
supernova remnant is reasonably responsible for the hard spectrum above 10 GeV.
Further studies of this region in the TeV regime is required, so that we can
perform physically meaningful comparisons of the $>$10 GeV spectrum and the TeV
spectrum.
