The prompt localization of gamma-ray burst ( GRB ) 050525A by Swift allowed the rapid follow-up of the afterglow .
The observations revealed that the optical afterglow had a major rebrightening starting at \sim 0.01 days and ending at \sim 0.03 days , which was followed by an initial power-law decay .
Here we show that this early emission feature can be interpreted as the reverse shock emission superposed by the forward shock emission in an interstellar medium environment .
By fitting the observed data , we further constrain some parameters of the standard fireball-shock model : the initial Lorentz factor of the ejecta \gamma _ { 0 } > 120 , the magnetic energy fraction \epsilon _ { B } > 4 \times 10 ^ { -6 } , and the medium density n < 2 { cm ^ { -3 } } .
These limits are consistent with those from the other very-early optical afterglows observed so far .
In principle , a wind environment for GRB 050525A is disfavored .