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tokens: the cascade emission is shown. The magnetic field in the comoving frame is then . Basically, a higher B leads to a more important synchrotron radiation, while a smaller B leads to a more important IC radiation. Since electrons usually emit higher-energy photons via IC radiation than via synchrotron radiation, the flux of the cascade emission at high energies becomes higher for a smaller B . On the other hand, more high-energy photons in turn produce more e ± pairs at high energies, making a harder electron spectrum than that in the case of a large B , as is shown in Figure 7 . This explains why the spectrum is also harder in the case of B = 0.01 than in the case of B = 1 at keV energies, where the emission is dominated by synchrotron radiation of these (relatively) low-energy electrons in both cases. One can see that the gamma-ray flux around 100 MeV is not very sensitive to the value of B . This is because the injection rate of the secondary electrons that emit 100 MeV photons is dominated by the γγ -annihilation process (i.e., in the right-hand side of Equation ( 3 )), mainly relies on the photon field, and does not change with the magnetic field. On the other hand, the jet is already an electron calorimeter even if only considering IC radiation under the benchmark parameters. Therefore, we expect the total photon production rate at a certain energy is roughly equal to the energy injection rate of the electrons that emit these photons (i.e., L γ ∼ L e ). A large B only changes the way the electrons radiate their energy away but does not increase the photon production rate. Although the energy of the gamma-ray-emitting electrons is different in the IC-dominated case with a small B from that in a synchrotron-dominated case with a large B , the resultant gamma-ray flux is at the the same level, since the energy injection rate of electrons in the relevant energy range is roughly constant with respect to electron energy (i.e., ). Figure 6. Same as Figure 3 , but for the equipartition coefficient for the magnetic field in the GRB jet B . The dashed and dotted lines correspond to the IC and synchrotron radiation, respectively. Figure 7. Quasi-steady-state spectrum of the cascaded electrons in the comoving frame of the GRB jet with fiducial parameters (except for the equipartition coefficient of the magnetic field). Purple, blue, and red curves are for B = 1, 0.1, and 0.01, respectively, while solid and dashed curves are the contribution by the BH and photomeson processes, respectively. 3. Application to LAT GRBs In this section, we apply our calculations to explain the high-energy spectrum of GRB 090926A, GRB 090902B, and GRB 080916C, which represent three different types of spectral feature. The origin of prompt keV/MeV emission is beyond the scope of this work, and we just regard it as a preexisting target photon field for the BH and photomeson processes. In our calculations below, we employ a flat spectrum for the injected proton spectrum ( s =