TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3275 SUBJECT: GRB050416: Refined Swift-XRT analysis DATE: 05/04/16 18:37:28 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT G. Cusumano, V. La Parola, T. Mineo, V. Mangano (IASF/Palermo), G. Chincarini, S. Campana, G. Tagliaferri, P. Romano, P. Giommi, M. Perri (INAF-OAB), M. Capalbi (ASDC), D. N. Burrows, J. A. Kennea (PSU), N. Gehrels (NASA/GSFC) We have analyzed the Swift-XRT data from the first orbit observation of GRB050416 (Sakamoto et al. 2005, GCN3264). The new refined coordinates are: RA(J2000) = 12:33:54.8 Dec(J2000) = +21:03:25.1 This position is 17.7 arcseconds from the BAT position given in GCN 3273 (Sakamoto et al. 2005) and 1.3 arcsec from the preliminary XRT position (GCN3268, Kennea et al. 2005). We estimate an uncertainty of 5 arcseconds radius (90% containment). The [0.2-10] keV light curve in Photon Counting (PC) mode starts ~90 seconds from the BAT trigger (T0). We clearly detect a rapidly fading source. The light curve can be fitted with a single power law with alpha= -0.6 +/- 0.3. A preliminary spectral fit to the PC data gives a spectral power law photon index of 2.02+/-0.21 in the [0.2-10] keV band, with a column density of (0.25+/-0.05)E22 cm^-2 (the Galactic line-of-sight absorption is 2.06E20 cm^-2). The average estimated unabsorbed 0.2-10 keV flux is 1.7E-11 erg cm^-2 s^-1.