GCN Circular 10201
P.A. Evans, K.L. Page (U. Leicester) and E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift-XRT team: We have analysed 2.4 ks of XRT data for GRB 091127 (Troja et al. GCN Circ. 10191), from 3.2 ks to 15.8 ks after the BAT trigger. The data comprise 761 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. Using 1066 s of PC mode data and 4 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 36.58290, -18.95250 which is equivalent to: RA (J2000): 02 26 19.89 Dec(J2000): -18 57 08.9 with an uncertainty of 1.4 arcsec (radius, 90% confidence). This is consistent with the optical/UV/IR position reported in GCN Circs 10192-4. The light curve can be modelled with a power-law decay with a decay index of alpha=1.09 (+/-0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.97 (+/-0.08). The best-fitting absorption column is 7.9 (+1.7, -1.6) x 10^20 cm^-2, in excess of the Galactic value of 2.8 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 1.98 (+0.15, -0.14) and a best-fitting absorption column of 9.8 (+3.3, -3.1) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.9 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. If the light curve continues to decay with a power-law decay index of 1.09, the count rate at T+24 hours will be 0.24 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.3 x 10^-12 (1.2 x 10^-11) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00377179. This circular is an official product of the Swift-XRT team.