TITLE: GCN CIRCULAR NUMBER: 14614 SUBJECT: GRB 130508A: Refined Swift-XRT analysis: Correction to GCN 14612 DATE: 13/05/09 11:03:24 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: GCN 14126 was sent in error, with several pieces of information missing, as new data were being processed as the circular was sent. The corrected refined XRT analysis is as follows: We have analysed 10 ks of XRT data for GRB 130508A (Holland et al. GCN Circ. 14607), from 134 s to 45.8 ks after the BAT trigger. The data comprise 53 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 305.3218, 34.9583 which is equivalent to: RA (J2000): 20 21 17.22 Dec(J2000): +34 57 29.9 with an uncertainty of 2.5 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.98 (+0.39, -0.28). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.0 (+0.6, -0.5). The best-fitting absorption column is 1.6 (+1.0, -0.8) x 10^22 cm^-2, in excess of the Galactic value of 7.7 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 1.0 x 10^-10 (1.3 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.6 (+1.0, -0.8) x 10^22 cm^-2 Galactic foreground: 7.7 x 10^21 cm^-2 Excess significance: 1.7 sigma Photon index: 1.0 (+0.6, -0.5) If the light curve continues to decay with a power-law decay index of 1.98, the count rate at T+24 hours will be 6.0 x 10^-6 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.1 x 10^-16 (7.8 x 10^-16) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00555413. This circular is an official product of the Swift-XRT team.