TITLE: GCN CIRCULAR NUMBER: 15040 SUBJECT: GRB 130725B: Swift-XRT refined Analysis DATE: 13/07/26 15:10:08 GMT FROM: Boris Sbarufatti at INAF-OAB/IASFPA B. Sbarufatti (INAF-OAB/PSU) and C. A. Swenson (PSU) report on behalf of the Swift-XRT team: We have analysed 8.2 ks of XRT data for GRB 130725B (Swenson et al. GCN Circ. 15029), from 53 s to 35.0 ks after the BAT trigger. The data comprise 235 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 6414 s of PC mode data and 9 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 = 214.24059, -11.12851 which is equivalent to: RA (J2000): 14h 16m 57.74s Dec(J2000): -11d 07' 42.6" with an uncertainty of 1.4 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=0.09 (+0.15, -0.18), followed by a break at T+534 s to an alpha of 0.95 (+/-0.05). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.97 (+0.17, -0.16). The best-fitting absorption column is 8.3 (+4.2, -3.2) x 10^20 cm^-2, consistent with the Galactic value of 5.2 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 3.6 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.3 (+4.2, -3.2) x 10^20 cm^-2 Galactic foreground: 5.2 x 10^20 cm^-2 Photon index: 1.97 (+0.17, -0.16) If the light curve continues to decay with a power-law decay index of 0.95, the count rate at T+24 hours will be 0.012 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x 10^-13 (5.5 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/00564028. This circular is an official product of the Swift-XRT team.