  GRB031203 was observed by XMM-Newton twice, first with an observation
beginning 6 hours after the burst, and again after 3 days. The afterglow had
average 0.2-10.0keV fluxes for the first and second observations of
4.2+/-0.1x10^-13 and 1.8+/-0.1x10^-13 erg/cm^2/s respectively, decaying very
slowly according to a power-law with an index of -0.55+/-0.05. The prompt soft
X-ray flux, inferred from a detection of the dust echo of the prompt emission,
strongly implies that this burst is very soft and should be classified as an
X-ray flash (XRF) and further, implies a steep temporal slope (<~-1.7) between
the prompt and afterglow phases or in the early afterglow, very different from
the later afterglow decay slope. A power-law (Gamma=1.90+/-0.05) with
absorption at a level consistent with the Galactic foreground absorption fits
the afterglow spectrum well. A bright, low-redshift (z=0.105) galaxy lies
within 0.5 arcsec of the X-ray position and is likely to be the GRB host. At
this redshift, GRB031203 is the closest GRB or XRF known after GRB980425. It
has a very low equivalent isotropic gamma-ray energy in the burst (~3x10^49
erg) and X-ray luminosity in the afterglow (9x10^42 erg/s at 10 hours), 3-4
orders of magnitude less than typical bursts, though higher than either the
faint XRF020903 or GRB980425. The rapid initial decline and subsequent very
slow fading of the X-ray afterglow is also similar to that observed in
GRB980425, indicating that GRB031203 may be representative of low luminosity
bursts.
