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 \times 10 ^ { -8 } ergs cm ^ { -2 } s ^ { -1 } Â 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 .