TITLE: GCN CIRCULAR NUMBER: 34444 SUBJECT: GRB 230815A: Swift-XRT refined Analysis DATE: 23/08/16 05:16:53 GMT FROM: Phil Evans at U of Leicester P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), D.N. Burrows (PSU), J. D. Gropp (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.0 ks of XRT data for GRB 230815A, from 117 s to 45.2 ks after the BAT trigger. The data comprise 574 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+6.1 ks) can be modelled with a power-law decay with a decay index of alpha=1.94 (+0.25, -0.29). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.92 (+0.06, -0.05). The best-fitting absorption column is 7.4 (+0.5, -0.4) x 10^21 cm^-2, in excess of the Galactic value of 4.9 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.94 (+0.18, -0.17) and a best-fitting absorption column of 9.1 (+1.7, -1.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.9 x 10^-11 (8.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 9.1 (+1.7, -1.5) x 10^21 cm^-2 Galactic foreground: 4.9 x 10^21 cm^-2 Excess significance: 4.5 sigma Photon index: 1.94 (+0.18, -0.17) If the light curve continues to decay with a power-law decay index of 1.94, the count rate at T+24 hours will be 2.5 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x 10^-13 (2.1 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/01185505. This circular is an official product of the Swift-XRT team.