  The collapse of a massive star is believed to be the most probable progenitor
of a long GRB. Such a star is expected to modify its environment by stellar
wind. The effect of such a circum-stellar wind medium is expected to be seen in
the evolution of a GRB afterglow, but has so far not been conclusively found.
We claim that a signature of wind to constant density medium transition of
circum-burst medium is visible in the afterglow of GRB 050319. Along with the
optical observations of the afterglow of GRB 050319 we present a model for the
multiband afterglow of GRB 050319. We show that the break seen in optical light
curve at $\sim$ 0.02 day could be explained as being due to wind to constant
density medium transition of circum-burst medium, in which case, to our
knowledge, this could be the first ever detection of such a transition at any
given frequency band. Detection of such a transition could also serve as a
confirmation of massive star collapse scenario for GRB progenitors, independent
of supernova signatures.
