  The Swift Gamma-Ray Burst Explorer performed its first autonomous, X-ray
follow-up to a newly detected GRB on 2005 January 17, within 193 seconds of the
burst trigger by the Swift Burst Alert Telescope. While the burst was still in
progress, the X-ray Telescope obtained a position and an image for an
un-catalogued X-ray source; simultaneous with the gamma-ray observation. The
XRT observed flux during the prompt emission was 1.1 x 10^{-8} ergs cm^{-2}
s^{-1} in the 0.5-10 keV energy band. The emission in the X-ray band decreased
by three orders of magnitude within 700 seconds, following the prompt emission.
This is found to be consistent with the gamma-ray decay when extrapolated into
the XRT energy band. During the following 6.3 hours, the XRT observed the
afterglow in an automated sequence for an additional 947 seconds, until the
burst became fully obscured by the Earth limb. A faint, extremely slowly
decaying afterglow, alpha=-0.21$, was detected. Finally, a break in the
lightcurve occurred and the flux decayed with alpha<-1.2$. The X-ray position
triggered many follow-up observations: no optical afterglow could be confirmed,
although a candidate was identified 3 arcsecs from the XRT position.
