TITLE: GCN CIRCULAR NUMBER: 28081 SUBJECT: GRB 200711A: Swift-XRT refined Analysis DATE: 20/07/12 06:34:40 GMT FROM: Phil Evans at U of Leicester J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (ASDC), V. D'Elia (ASDC), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and F.E. Marshall report on behalf of the Swift-XRT team: We have analysed 6.9 ks of XRT data for GRB 200711A (Marshall et al. GCN Circ. 28078), from 150 s to 40.4 ks after the BAT trigger. The data comprise 29 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. Using 1145 s of PC mode data and 2 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 = 285.97020, -0.14708 which is equivalent to: RA (J2000): 19h 03m 52.85s Dec(J2000): -00d 08' 49.5" with an uncertainty of 1.6 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=0.51 (+0.13, -0.14), followed by a break at T+3349 s to an alpha of 1.41 (+/-0.09). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.01 (+0.22, -0.21). The best-fitting absorption column is 1.65 (+0.30, -0.27) x 10^22 cm^-2, in excess of the Galactic value of 5.7 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.6 x 10^-11 (1.2 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.65 (+0.30, -0.27) x 10^22 cm^-2 Galactic foreground: 5.7 x 10^21 cm^-2 Excess significance: 6.5 sigma Photon index: 2.01 (+0.22, -0.21) If the light curve continues to decay with a power-law decay index of 1.41, the count rate at T+24 hours will be 9.6 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.4 x 10^-13 (1.1 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00981957. This circular is an official product of the Swift-XRT team.