TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3877 SUBJECT: GRB050824: decay of the XRT light curve and updated X-ray spectrum DATE: 05/08/25 17:27:22 GMT FROM: Sergio Campana at INAF-OAB S. Campana (INAF-OAB), A. Moretti (INAF-OAB), V. Mangano (INAF-IASF Palermo), D.N. Burrows (PSU), report: We have analyzed 13 ks of Swift XRT data of GRB 050824 (Campana et al., GCN3866). The 0.2-10 keV light curve XRT (started 6089 seconds after the BAT trigger) now shows an indication of a temporal decay with a power law index of -0.4+/-0.2 (90% confidence level). The power law fit is better than a constant fit at a 3.3 sigma level (F-test). This indicates that the source suggested in the previous XRT circular (Campana et al., GCN3872) is the X-ray afterglow of GRB050824. The 307 photons in the 0.3-10 keV evergy band were also used for spectral analysis. We fixed the column density to the Galactic value (3.6x10^20 cm-2) and added a free local absorption at z=0.83 (Fynbo et al., GCN3874) plus a power law. We found an accepetable model (chi2_red=1.01) with a NH_loc=(1.7+/-1.3)x10^21 cm-2 and a power law photon index of 2.0+/-0.2 (90% confidence level). [GCN OPS NOTE(25aug05): Per author's request, "...afterglow of GRB050724" was changed to "...afterglow of GRB050824".]