TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3669 SUBJECT: GRB 050724: early Swift XRT analysis results DATE: 05/07/24 18:30:47 GMT FROM: Pat Romano at OAB-Swift P. Romano, A. Moretti, S. Covino (INAF-OAB), L.A. Antonelli(IANF-OAR), D.N. Burrows, D. Grupe (PSU), M. Chester (PSU), G. Chincarini, G. Tagliaferri (INAF-OAB), P. Boyd (GSFC-UMBC) on behalf of the Swift-XRT Team report. We have analyzed the Swift XRT data from the first orbit observation of GRB 050724 (Covino et al., GCN 3665). The new refined coordinates are: RA(J2000) = 16h 24m 45s Dec(J2000) = -27 32 25.2. This position is 65 arcseconds from the refined BAT position given in GCN 3667 (H. Krimm et al), and 9 arcseconds from the XRT position given in GCN 3665. We estimate an uncertainty of 6.3 arcseconds radius (90% containment). However, we note that there is accumulating evidence of a time-dependent systematic shift in XRT positions derived from ground-processed data towards lower declinations than the optical counterparts. This effect is being investigated but is not yet understood. Extrapolation of earlier positional errors suggests that the correct position could be approximately 7 arcseconds north of the position given above, which would be close to the on-board position given in GCN 3665. A preliminary spectral fit (simple absorbed power-law) to the WT data yields a photon index of 1.93-/+0.05 in the [0.5-10] keV band. The derived NH is (5.7)E21 cm^-2, which is higher than the Galactic value (1.46E+21 cm-2; Dickey & Lockman 1990). The average (79-342 seconds from trigger) estimated unabsorbed 0.5-10 keV flux is 5.3E-9 ergs/s/cm2. The light curves in Windowed Timing (WT) and Photon Counting (PC) mode start 79 and 343 seconds from the BAT trigger (T0), and they show a fading afterglow which can be fitted with a broken power law of slopes -3.2+/-0.1 and -0.8+/-0.2. The unabsorbed 0.5-10.0 keV flux at 24 hours after the burst is then estimated to 9E-14 ergs/s/cm2.