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{\it Fermi} satellite has detected extra spectral components in GeV energyrange in several GRBs. Those components have power-law shapes, which maycontribute to also X-ray band. The limited photon statistics make it difficultto determine the origin of GeV photons, namely internal or external shocks. Wetry to explain the extra components with our numerical simulations based oninternal dissipation picture. Our leptonic model may reproduce not only the GeVexcess via SSC emission but also the low-energy excess via the late synchrotronemission from remnant electrons. The hadronic models also reproduce keV-GeVpower-law components by synchrotron and SSC emissions from secondaryelectron-positron pairs. In most cases the hadronic models require a muchlarger energy of protons than gamma-rays. However, the keV-GeV flat spectradetected in GRB 090902B is well explained with a comparable energy in protonsand gamma-rays Finally, we discuss both advantages and weaknesses for both theleptonic and hadronic models. To overcome difficulties in internal dissipationmodels, we propose introduction of continuous acceleration similar to thesecond-order Fermi acceleration.

Leptonic and Hadronic Models for the Extra Components in Fermi-LAT GRBs