  Correlations between optical flashes and gamma-ray emissions in gamma-ray
bursts have been searched in order to clarify the question whether these
emissions occur at internal and/or external shocks. Among the most powerful
gamma-ray bursts ever recorded are GRB 080319B and GRB 130427A which at early
phase presented bright optical flashes possible correlated with $\gamma$-ray
components. Additionally, both bursts were fortuitously located within the
field of view of the TeV $\gamma$-ray Milagro and HAWC observatories, and
although no statistically significant excess of counts were collected, upper
limits were placed on the GeV - TeV emission. Considering the synchrotron
self-Compton emission from internal shocks and requiring the GeV-TeV upper
limits we found that the optical flashes and the $\gamma$-ray components are
produced by different electron populations. Analyzing the optical flashes
together the multiwavelength afterglow observation, we found that these flashes
can be interpreted in the framework of the synchrotron reverse-shock model when
outflows have arbitrary magnetizations.
