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The extremely bright optical flash that accompanied GRB 080319B suggested, atfirst glance, that the prompt $\gamma$-rays in this burst were produced bySynchrotron self Compton (SSC). We analyze here the observed optical and$\gamma$ spectrum. We find that the very strong optical emission poses, due toself absorption, very strong constraints on the emission processes and put theorigin of the optical emission at a very large radius, almost inconsistent withinternal shock. Alternatively it requires a very large random Lorentz factorfor the electrons. We find that SSC could not have produced the prompt$\gamma$-rays. We also show that the optical emission and the $\gamma$ rayscould not have been produced by synchrotron emission from two populations ofelectron within the same emitting region. Thus we must conclude that theoptical and the $\gamma$-rays were produced in different physical regions. Apossible interpretation of the observations is that the $\gamma$-rays arosefrom internal shocks but the optical flash resulted from external shockemission. This would have been consistent with the few seconds delay observedbetween the optical and $\gamma$-rays signals.

Clues from the prompt emission of GRB 080319B