TITLE: GCN CIRCULAR NUMBER: 28341 SUBJECT: GRB 200901A: Swift-XRT refined Analysis DATE: 20/09/01 18:09:03 GMT FROM: Boris Sbarufatti at PSU J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU) and K. K. Simpson (PSU) report on behalf of the Swift-XRT team: We have analysed 2.5 ks of XRT data for GRB 200901A (Simpson et al. GCN Circ. 28335), from 3.1 ks to 11.1 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. Using 1707 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 = 61.78319, -59.89084 which is equivalent to: RA (J2000): 04h 07m 07.97s Dec(J2000): -59d 53' 27.0" 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=0.95 (+0.28, -0.24). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.31 (+0.30, -0.28). The best-fitting absorption column is 2.2 (+0.9, -0.8) x 10^21 cm^-2, in excess of the Galactic value of 1.5 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.0 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.2 (+0.9, -0.8) x 10^21 cm^-2 Galactic foreground: 1.5 x 10^20 cm^-2 Excess significance: 4.2 sigma Photon index: 2.31 (+0.30, -0.28) 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 7.9 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x 10^-13 (3.8 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/00994143. This circular is an official product of the Swift-XRT team.