TITLE: GCN CIRCULAR NUMBER: 27923 SUBJECT: GRB 200612A: Swift-XRT refined Analysis DATE: 20/06/13 00:13:52 GMT FROM: Phil Evans at U of Leicester A. D'Ai (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB) and E. Sonbas report on behalf of the Swift-XRT team: We have analysed 7.4 ks of XRT data for GRB 200612A (Sonbas et al. GCN Circ. 27915), from 93 s to 63.5 ks after the BAT trigger. The data comprise 281 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 27921). The late-time light curve (from T0+3.7 ks) can be modelled with a power-law decay with a decay index of alpha=1.37 (+/-0.09). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.07 (+/-0.05). The best-fitting absorption column is 9.1 (+2.3, -2.1) x 10^20 cm^-2, in excess of the Galactic value of 3.7 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.06 (+0.19, -0.17) and a best-fitting absorption column of 5.7 (+4.1, -2.0) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.1 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.7 (+4.1, -2.0) x 10^20 cm^-2 Galactic foreground: 3.7 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.06 (+0.19, -0.17) If the light curve continues to decay with a power-law decay index of 1.37, the count rate at T+24 hours will be 0.010 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.2 x 10^-13 (3.7 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/00977310. This circular is an official product of the Swift-XRT team.