SIMBAD references

We have collected and analyzed data taken in different spectral bands (from X-ray to optical and infrared) of the field of GRB 031220 and we present results of such multiband observations. Comparison between images taken at different epochs in the same filters did not reveal any strong variable source in the field of this burst. X-ray analysis shows that only two of the seven Chandra sources have a significant flux decrease and seem to be the most likely afterglow candidates. Both sources do not show the typical values of the R-K' colour but they appear to be redder. However, only one source has an X-ray decay index (1.3±0.1) that is typical for observed afterglows. We assume that this source is the best afterglow candidate and we estimate a redshift of 1.90±0.30. Photometric analysis and redshift estimation for this object suggest that this GRB can be classified as a Dark Burst and that the obscuration is the result of dust extinction in the burst circum medium or inside the host galaxy.