  One of the major results from the study of gamma-ray bursts with the Fermi
Gamma-ray Space Telescope has been the confirmation that several emission
components can be present in the energy spectrum. Here we reanalyse the
spectrum of GRB 080825C using data from the Fermi LAT and GBM instruments.
Although fairly weak, it is the first gamma-ray burst detected by the
Fermi-LAT. We improve on the original analysis by using the LAT Low Energy
(LLE) events covering the 30-00 MeV band. We find evidence of an additional
component above the main emission peak (modelled using a Band function) with a
significance of 3.5 $\sigma$ in 2 out of the 4 time bins. The component is well
fitted by a Planck function, but shows unusual behaviour: the peak energy
increases in the prompt emission phase, reaching energies of several MeV. This
is the first time such a trend has been seen, and implies that the origin of
this component is different from those previously detected. We suggest that the
two spectral components likely arise in different regions of the outflow, and
that strong constraints can be achieved by assuming one of them originates from
the photosphere. The most promising model appears to be that the high-energy
peak is the result of photospheric emission in a Poynting flux dominated
outflow where the magnetisation increases with time.

High Energy Astrophysical Phenomena