  We present a multi-wavelength analysis of gamma-ray burst GRB 090727, for
which optical emission was detected during the prompt gamma-ray emission by the
2-m autonomous robotic Liverpool Telescope and subsequently monitored for a
further two days with the Liverpool and Faulkes telescopes. Within the context
of the standard fireball model, we rule out a reverse shock origin for the
early time optical emission in GRB 090727 and instead conclude that the early
time optical flash likely corresponds to emission from an internal dissipation
processes. Putting GRB 090727 into a broader observational and theoretical
context, we build a sample of 36 gamma-ray bursts (GRBs) with contemporaneous
early time optical and gamma-ray detections. From these GRBs, we extract a
sub-sample of 18 GRBs, which show optical peaks during prompt gamma-ray
emission, and perform detailed temporal and spectral analysis in gamma-ray,
X-ray, and optical bands. We find that in most cases early time optical
emission shows sharp and steep behaviour, and notice a rich diversity of
spectral properties. Using a simple internal shock dissipation model, we show
that the emission during prompt GRB phase can occur at very different
frequencies via synchrotron radiation. Based on the results obtained from
observations and simulation, we conclude that the standard external shock
interpretation for early time optical emission is disfavoured in most cases due
to sharp peaks ($\Delta t/t < 1$) and steep rise/decay indices, and that
internal dissipation can explain the properties of GRBs with optical peaks
during gamma-ray emission.
