GCN Circular 3659
P. Romano (INAF-OAB), L.A. Antonelli (INAF-OAR), G. Chincarini, A. Moretti, G. Tagliaferri (INAF-OAB), K. Page (U. Leicester), F. Marshall (GSFC), P. Boyd (GSFC-UMBC) on behalf of the Swift-XRT team: We have analyzed the Swift XRT data from the first orbit observation of GRB 050721A (Antonelli et al., GCN 3654). The new refined coordinates are: RA(J2000) = 16h 53m 44.9s Dec(J2000) = -28 22 51.7 This position is 41 arcseconds from the BAT position given in GCN 3654. We estimate an uncertainty of 6 arcseconds radius (90% containment). A preliminary spectral fit (simple absorbed power-law) to the combined PC and WT data yields a photon index of 1.7+/-0.1 in the [0.5-10] keV band. The derived NH is 3.16E21 cm^-2, which is higher than the Galactic value (1.57E21 cm^-2; Dickey & Lockman 1990). The average (194-323 seconds from trigger for WT and 324-463 seconds from trigger for PC) estimated unabsorbed 0.5-10 keV flux is then 3.5E-10 ergs/s/cm^2. The light curves in Windowed Timing (WT) and Photon Counting (PC) mode start 194 and 324 seconds from the BAT trigger (T0), and they show a fading afterglow with a preliminary decay slope -1.99+/-0.07 (first orbit only). The unabsorbed 0.5-10.0 keV flux at 1 hour after the burst is estimated to be 5E-12 ergs/s/cm^2.