TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3928 SUBJECT: GRB 050904: Did SWIFT/XRT see the prompt GRB emission ? DATE: 05/09/06 14:27:48 GMT FROM: Jean-Luc Atteia at Lab d Astrophys.,OMP,Toulouse J-L. Atteia (LAT-OMP) communicates: The high redshift of GRB 050904 suggests a possible interpretation of the XRT observations reported in GCNC 3920 (T. Mineo et al.) as the *prompt emission* of the burst. - The maximum effective area of SWIFT/XRT (2 keV) corresponds to a restframe energy of ~14 keV for a source at redshift z=6.1. - The time of the first XRT flare is 466/(7.1) ~ 66 sec in the restframe. - The spectral index of -1.33 is suggestive of the spectral index of the prompt emission below the the break energy (Epeak). All these numbers are compatible with an interpretation of the early SWIFT/XRT observations in terms of GRB prompt emission. In view of this possibility, further information on the duration of GRB 050904, would be of great interest.