  Lyutikov (astro-ph/0503505) raised a valid point that for shock deceleration
of a highly magnetized outflow, the fate of the magnetic fields after shock
crossing should be considered. However, his comment that the deceleration
radius should be defined by the total energy rather than by the baryonic
kinetic energy is incorrect. As strictly derived from the shock jump conditions
in Zhang & Kobayashi (2005), during the reverse shock crossing process the
magnetic energy is not tapped. As a result, the fireball deceleration radius is
defined by the baryonic energy only. The magnetic energy is expected to be
transferred to the circumburst medium after the reverse shock disappears. The
evolution of the system then mimicks a continuously-fed fireball. As a result,
Lyutikov's naive conclusion that the forward shock dynamics is independent on
the ejecta content is also incorrect. The shock deceleration dynamics and the
reverse shock calculation presented in Zhang & Kobayashi (2005) are robust and
correct.
