  The synchrotron optical flash caught in GRB 990123 overlaps with the MeV
radiation front, and the optical-emitting electrons must also produce GeV-TeV
emission by inverse Compton scattering of MeV photons. The ultra-high-energy
flash can be much stronger than its optical counterpart. We also note that
Compton cooling by MeV photons immediately terminates the optical emission
unless the fireball Lorentz factor exceeds 10^3. Severe Compton losses may
explain the non-detections of optical flashes in several long GRBs. Such failed
optical flashes should be especially efficient GeV producers and likely to
develop e+- cascades. This probably happened in GRB 941017, and its mysterious
high-energy component is well explained by Compton upscattering of GRB photons
at the fireball deceleration radius. The proposed mechanism of GeV emission
should not work for short gamma-ray bursts that early decouple from the
fireball and avoid interaction with the electrons in the deceleration flash.
Observations by Swift and GLAST will provide an opportunity to test these
expectations. The existing data for GRB 990123 already impose interesting
constraints on the explosion.
