The inverse compton emission spectra in the very early afterglows of gamma-ray bursts

We calculate the spectra of inverse Compton (IC) emissions in gamma-ray bur st (GRB) shocks produced when relativistic ejecta encounters the external i nterstellar medium, assuming a broken power-law approximation to the synchr otron seed spectrum. Four IC processes, including the synchrotron self-Comp ton (SSC) processes in GRB forward and reverse shocks, and two combined-IC processes (i.e., scattering of reverse shock photons on the electrons in fo rward shocks and forward shock photons on the electrons in reverse shocks), are considered. We find that the SSC emission from reverse shocks dominate s over other emission processes in energy bands from tens of MeV to tens of GeV, for a wide range of shock parameters. This mechanism may be responsib le for the prompt high-energy gamma rays detected by EGRET. At TeV energy b ands, however, the combined-IC emissions and/or the SSC emission from the f orward shocks become increasingly dominant for a moderately steep distribut ion of shocked electrons.