TITLE: GCN CIRCULAR NUMBER: 22394 SUBJECT: GRB 180205A: Swift-XRT refined Analysis DATE: 18/02/06 04:46:03 GMT FROM: Phil Evans at U of Leicester K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.A. Kennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.0 ks of XRT data for GRB 180205A (Evans et al. GCN Circ. 22381), from 180 s to 33.8 ks after the BAT trigger. The data comprise 85 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. Using 3849 s of PC mode data and 7 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 = 126.81966, +11.54210 which is equivalent to: RA (J2000): 08h 27m 16.72s Dec(J2000): +11d 32' 31.6" with an uncertainty of 1.5 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=4.8 (+0.6, -0.5), followed by a break at T+279 s to an alpha of 1.00 (+/-0.04). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.72 (+0.18, -0.17). The best-fitting absorption column is 8.7 (+2.8, -2.5) x 10^21 cm^-2, at a redshift of 1.409, in addition to the Galactic value of 3.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.89 (+0.15, -0.14) and a best-fitting absorption column of 3.1 (+3.0, -2.6) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 3.4 x 10^20 cm^-2 Intrinsic column: 3.1 (+3.0, -2.6) x 10^21 cm^-2 at z=1.409 Photon index: 1.89 (+0.15, -0.14) If the light curve continues to decay with a power-law decay index of 1.00, the count rate at T+24 hours will be 0.013 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x 10^-13 (5.2 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/00808625. This circular is an official product of the Swift-XRT team.