TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2476 SUBJECT: GRB 031203: Deep NIR NTT & VLT observations DATE: 03/12/06 14:16:27 GMT FROM: Gianpiero Tagliaferri at OAB-INAF GRB 031203: Deep NIR NTT & VLT observations G. Tagliaferri, S. Covino, D. Fugazza, S. Campana, A. Simoncelli (INAF-OAB) G. Chincarini (UNIMIB & INAF-OAB), L. Stella (INAF-OAR) On December 5th, at 06:12 UT, we started observing in JHKs filters with ISAAC at the VLT-UT1 telescope the XMM source S1 (Santos-Lleo & Calderon GCN2464). In the XMM error box of 6" around S1 we detect the source already seen in the previous night with the NTT (Zerbi et al. GCN2471, see also Hsia et al. GCN2470). With ISAAC we obtained the following magnitudes (based on 2MASS stars): J=18.40+/-0.15, H=17.80+/-0.15 and Ks=16.70+/-0.15. A comparison between the NTT values on December 4 and the VLT one of the following night shows that this object faded by few tens of magnitude. Given that this object was already detected in archive images (Bloom et al. GCN2472), it is probably a variable star. In the XMM error box with ISAAC we detect also another source with J=21.05+/-0.25 (not visible in H and Ks). This object was already present in the SofI J image and it does not seem to have varied. We did not see any variable source in an area of 20 arcsecond radius around the XMM S1 position. Therefore, we have no indication of a transient associated with GRB 031203. However, note that the VLT images do not cover the full INTEGRAL error box, in particular the area around the XMM S2 source is not in the FoV. For the NTT SofI Ks finding charts, see http://www.merate.mi.astro.it/~taglia/GRB031203.jpg We thank the ESO La Silla and Paranal staff for their prompt reaction and support. This message can be cited.