High Energy Photons From Gamma Ray Bursts
  Emission of high energy (HE) photons above 100 MeV that is delayed and lasts
much longer than the prompt MeV emission has been detected from several long
duration gamma ray bursts (LGRBs) and short hard bursts (SHBs) by the Compton,
Fermi and AGILE gamma ray observatories. In this paper we show that the main
observed properties of this HE emission are those predicted by the cannonball
(CB) model of GRBs: In the CB model all the observed radiations in a GRB are
produced by the interaction of a highly relativistic jet of plasmoids (CBs)
with the environment. The prompt X-ray and MeV $\gamma$-ray pulses are produced
by inverse Compton scattering (ICS) of glory photons -photons scattered/emitted
into a cavity created by the wind/ejecta blown from the progenitor star or a
companion star long before the GRB- by the thermal electrons in the CBs. A
simultaneous optical and high energy emission begins shortly after each MeV
pulse when the CB collides with the wind/ejecta, and continues during the
deceleration of the CB in the interstellar medium. The optical emission is
dominated by synchrotron radiation (SR) from the swept-in and knocked-on
electrons which are Fermi accelerated to high energies by the turbulent
magnetic fields in the CBs, while ICS of these SR photons dominates the
emission of HE photons. The lightcurves of the optical and HE emissions have
approximately the same temporal behaviour but have different power-law spectra.
The emission of very high energy (VHE) photons above 100 TeV is dominated by
the decay of $\pi^0$'s produced in hadronic collisions of Fermi accelerated
protons in the CBs. The CB model explains well all the observed radiations,
including the high energy radiation from both LGRBs and SHBs as demonstrated
here for GRB 090902B and SHB 090510.
