  We investigate two high energy radiation mechanisms, the proton synchrotron
and the electron inverse Compton emission, and explore their possible
signatures in the broad-band spectra and in the keV to GeV light curves of
gamma-ray burst afterglows. We develop a simple analytical approach, allowing
also for the effects of photon-photon pair production, and explore the
conditions under which one or the other of these components dominates. We
identify three parameter space regions where different spectral components
dominate: (I) a region where the proton synchrotron and other hadron-related
emission components dominate, which is small; (II) a region where the electron
inverse Compton component dominates, which is substantial; (III) a third
substantial region where electron synchrotron dominates. We discuss the
prospects and astrophysical implications of directly detecting the inverse
Compton and the proton high energy components in various bands, in particular
in the GeV band with future missions such as GLAST, and in the X-ray band with
Chandra. We find that regime II parameter space is the most favorable regime
for high energy emission. The inverse Compton component is detectable by GLAST
within hours for bursts at typical cosmological distances, and by Chandra in
days if the ambient density is high.
