  We report the first detection of a time-dependent, dust-scattered X-ray halo
around a gamma-ray burst. GRB 031203 was observed by XMM-Newton starting six
hours after the burst. The halo appeared as concentric ring-like structures
centered on the GRB location. The radii of these structures increased with time
as t^{1/2}, consistent with small-angle X-ray scattering caused by a large
column of dust along the line of sight to a cosmologically distant GRB. The
rings are due to dust concentrated in two distinct slabs in the Galaxy located
at distances of 880 and 1390 pc, consistent with known Galactic features. The
halo brightness implies an initial soft X-ray pulse consistent with the
observed GRB.
