  GRB050223 was discovered by the Swift Gamma-Ray Burst Explorer on 23 February
2005 and was the first Gamma-Ray Burst to be observed by both Swift and
XMM-Newton. At the time of writing (May 2005), it has one of the faintest GRB
afterglows ever observed. The spacecraft could not slew immediately to the
burst, so the first X-ray and optical observations occurred approximately 45
minutes after the trigger. Although no optical emission was found by any
instrument, both Swift and XMM-Newton detected the fading X-ray afterglow.
Combined data from both of these observatories show the afterglow to be fading
monotonically as 0.99 +0.15/-0.12 over a time frame between 45 minutes to 27
hours post-burst. Spectral analysis, allowed largely by the higher through-put
of XMM-Newton, implies a power-law with a slope of Gamma=1.75 +0.19/-0.18 and
shows no evidence for absorption above the Galactic column of 7 x 10^20 cm^-2.
  From the X-ray decay and spectral slopes, a low electron power-law index of p
= 1.3-1.9 is derived; the slopes also imply that a jet-break has not occured up
to 27 hours after the burst. The faintness of GRB050223 may be due to a large
jet opening or viewing angle or a high redshift.
