TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4347 SUBJECT: GRB051211B: XRT refined analysis DATE: 05/12/13 16:04:25 GMT FROM: Valentina La Parola at INAF-IASPA V. La Parola, V. Mangano, G. Cusumano (INAF-IASF), C. Pagani (INAF-OAB), and D. N. Burrows (PSU), D. Hinshaw (GSFC-SPSYS), F. Marshall (GSFC), report on behalf of the Swift XRT team: We report on further analysis of the XRT observation of GRB051211B (Mereghetti et al., GCN 4327; Pagani et al, GCN 4332; La Parola et al., GCN 4338). The XRT observation begins 10.8 ksec after the INTEGRAL trigger. We see a flat phase with a break at 18 ksec from the burst trigger, then the X-ray light-curve decays as a powerlaw with slope -1.16 +/- 0.18. The spectrum of the PC data can be modelled with an absorbed power-law with photon index Gamma = 2.0+/-0.3 (90% confidence level). The absorbing column best fit value is (4.1 +/- 1.3)e21 cm-2, consistent with the Galactic value of 3.3e21 cm-2 The flux at T+24h is 4.4e-13 erg cm^-2 s^-1