TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3731 SUBJECT: GCN 050801: early Swift XRT analysis results DATE: 05/08/02 04:38:24 GMT FROM: Matteo Perri at ISAC/ASDC M. Perri, M. Capalbi, P. Giommi (ASDC), J. Kennea, D.N. Burrows, P. Meszaros (PSU), K. Hinshaw (GSFC-SPSYS) report on behalf of the Swift XRT team: We have analyzed the Swift XRT data from the first orbit observation of GRB 050801 (Band et al., GCN 3725). A fading, previously uncatalogued, point source at the following coordinates is detected in the field: RA(J2000) = 13h 36m 36.0s Dec(J2000) = -21d 55' 42" This position is 83 arcseconds from the BAT position given in GCN 3725 (Band et al.) and 8.5 arcsec from the ROTSE-III position reported in GCN 3723 (Rykoff et al.). The source is close to a bad column of the CCD and we estimate an uncertainty of 10 arcseconds radius in the derived position. Data in Photon Counting (PC) mode starts at 18:29:31 UT, 89 seconds from the BAT trigger. The 0.3-10 keV afterglow light curve shows a flat slope from T+89s to T+300s and then declines following a power law with decay index alpha=-1.3+/-0.3 up to T+990s, when first orbits ends. A preliminary spectral fit in the 0.3-10 keV energy band to the first orbit gives a spectral power law photon index of 1.8+/-0.3 with Nh=5.7E20 cm^-2. In the time range 89-990 seconds from trigger the average unabsorbed 0.5-10 keV flux is 2.6E-11 erg cm^-2 s^-1.