TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3983 SUBJECT: GRB 050915: Swift XRT refined analysis DATE: 05/09/15 18:14:14 GMT FROM: Dirk Grupe at PSU/Swift-XRT D. Grupe, J. Kennea, D. Burrows (PSU), and N. Gehrels GSFC) on report behalf of the Swift XRT team: We have analyzed the Swift XRT data of the first three orbits of GRB050915 (Grupe et al. GCN 3977, BAT trigger 155242). The new refined position based on the SDC quicklook data is: RA (J2000) = 05h26m44.6s DEC(J2000) = -28d01m01.0s This position is 5.8 arcsec away from the XRT position reported by Kennea et al. (GCN 3979) based on the preliminary data analysis and 29 arcsec from the refined BAT position (Barthelmy et al., GCN 3982). The WT data show a spectrum that can be fitted by a single power law with excess absorption above the Galactic value. The X-ray energy spectral slope is beta-x = 1.33+/-0.23. The integrated 0.3-10.0 keV Flux during the WT observation was 4.6e-10 ergs/s/cm2 (corrected for absorption). The XRT light curve started 87s after the burst and shows a rapidly decaying source after a light increased in flux at the beginning. The decay slope is alpha-1 = 3.00+/-0.14. The light curves shows a clear break in the PC mode data at 210s after the burst and flattens to a decay slope alpha-2=0.75 ±0.04. Extrapolating this light curve we estimate the 0.3-10.0 flux to be in the order of 5e-13 ergs/s/cm2 24 hours after the burst. However, this estimate does not take any late time break, which are usually observed in GRBs several hours after the burst, into consideration.