GCN Circular 14430
K.L. Page (U. Leicester) and S. R. Oates (UCL-MSSL) report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 130420B (Oates et al. GCN Circ. 14411), from 39 s to 39.9 ks after the BAT trigger. The data comprise 18 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 2638 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 = 183.12838, +54.39054 which is equivalent to: RA (J2000): 12h 12m 30.81s Dec(J2000): +54d 23' 26.0" 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=1.11 (+0.09, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 (+/-0.4). The best-fitting absorption column is 6.8 (+9.6, -5.4) x 10^20 cm^-2, consistent with the Galactic value of 1.4 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.8 (+9.6, -5.4) x 10^20 cm^-2 Galactic foreground: 1.4 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.0 (+/-0.4) If the light curve continues to decay with a power-law decay index of 1.11, the count rate at T+24 hours will be 2.0 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.1 x 10^-14 (8.5 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00553996. This circular is an official product of the Swift-XRT team.