TITLE: GCN CIRCULAR NUMBER: 23857 SUBJECT: GRB 190204A: Swift-XRT refined Analysis DATE: 19/02/04 11:45:54 GMT FROM: Phil Evans at U of Leicester J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU) and A.Y. Lien report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 190204A (Lien et al. GCN Circ. 23852), from 81 s to 13.0 ks after the BAT trigger. The data comprise 926 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 351.4775, +54.8766 which is equivalent to: RA (J2000): 23 25 54.59 Dec(J2000): +54 52 35.7 with an uncertainty of 3.6 arcsec (radius, 90% confidence). The late-time light curve (from T0+4.8 ks) can be modelled with a power-law decay with a decay index of alpha=1.36 (+/-0.16). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.740 (+0.022, -0.018). The best-fitting absorption column is consistent with the Galactic value of 4.4 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.83 (+0.12, -0.11) and a best-fitting absorption column of 5.4 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.6 x 10^-11 (6.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.4 (+0.8, -0.7) x 10^21 cm^-2 Galactic foreground: 4.4 x 10^21 cm^-2 Excess significance: 2.4 sigma Photon index: 1.83 (+0.12, -0.11) If the light curve continues to decay with a power-law decay index of 1.36, the count rate at T+24 hours will be 9.9 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x 10^-13 (6.8 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/00887579. This circular is an official product of the Swift-XRT team.