GCN Circular 13838
V. D'Elia (ASDC) and P. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 6.7 ks of XRT data for GRB 121001A (D'Elia et al. GCN Circ. 13831), from 111 s to 41.8 ks after the BAT trigger. The data comprise 93 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. Using 2340 s of PC mode data and 3 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 = 276.03227, -5.66587 which is equivalent to: RA (J2000): 18h 24m 07.74s Dec(J2000): -05d 39' 57.1" with an uncertainty of 1.8 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.30 (+/-0.04). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.28 (+0.25, -0.24). The best-fitting absorption column is 7.6 (+2.4, -2.0) x 10^21 cm^-2, in excess of the Galactic value of 4.5 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 7.6 x 10^-11 (9.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.6 (+2.4, -2.0) x 10^21 cm^-2 Galactic foreground: 4.5 x 10^21 cm^-2 Excess significance: 2.5 sigma Photon index: 1.28 (+0.25, -0.24) If the light curve continues to decay with a power-law decay index of 1.30, the count rate at T+24 hours will be 2.1 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x 10^-13 (2.1 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00535026. This circular is an official product of the Swift-XRT team.