  Swift discovered the high redshift GRB 050319 with the Burst Alert Telescope
and began observing with its narrow field instruments only 225 s after the
burst onset. The afterglow X-ray emission was monitored by the XRT up to 28
days after the burst. The light curve shows a decay with three different
phases, each characterized by a distinct slope: an initial steep decay with a
power law index of ~ 5.5, a second phase characterized by a flat decay slope of
\~ 0.54, and a third phase with a decay slope of ~ 1.14. During the first phase
the spectral energy distribution is softer than in the following two phases and
the photon index is consistent with the GRB prompt spectrum. The extrapolation
of the BAT light curve to the XRT band suggests that the initial fast decaying
phase of the XRT afterglow might be the low energy tail of the prompt emission.
The second break in the afterglow light curve occurs about 27000 s after the
burst. The spectral energy distribution before and after the second break does
not change and it can be tentatively interpreted as a jet break or the end of a
delayed or continuous energy injection phase.
