Interpreting the high energy emission of Fermi GRBs
  The high energy emission from Gamma-ray Bursts has some interesting features,
including the absence of the GeV excess in the prompt spectrum, the delayed
onset of the GeV emission, and the longer duration of the GeV emission than the
prompt soft gamma-ray emission. We suggest that the non-detection of a GeV
excess in most GRB spectrum may favor the magnetic fireball model and the early
prompt emission may be dominated by the photosphere radiation of the breakout
material and is thus very soft. The synchrotron radiation in GeV band can be
the dominant component of the high energy afterglow emission, as speculated in
GRB 080319B and then confirmed in GRB 080916C and GRB 090510. A simple estimate
of the thermal radiation of the breakout material has been presented.
