TITLE: GCN CIRCULAR NUMBER: 30483 SUBJECT: GRB 210722A: Swift-XRT refined Analysis DATE: 21/07/23 14:27:18 GMT FROM: Phil Evans at U of Leicester K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto) and P. D'Avanzo report on behalf of the Swift-XRT team: We have analysed 6.3 ks of XRT data for GRB 210722A (D'Avanzo et al. GCN Circ. 30475), from 91 s to 47.1 ks after the BAT trigger. The data comprise 294 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. Using 3301 s of PC mode data and 8 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 = 27.03023, -6.34758 which is equivalent to: RA (J2000): 01h 48m 07.26s Dec(J2000): -06d 20' 51.3" with an uncertainty of 2.0 arcsec (radius, 90% confidence). The late-time light curve (from T0+4.5 ks) can be modelled with a power-law decay with a decay index of alpha=1.31 (+0.10, -0.09). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.20 (+/-0.05). The best-fitting absorption column is 4.2 (+1.0, -0.9) x 10^20 cm^-2, in excess of the Galactic value of 2.2 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.84 (+0.11, -0.10) and a best-fitting absorption column of 3.5 (+2.4, -1.2) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (3.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.5 (+2.4, -1.2) x 10^20 cm^-2 Galactic foreground: 2.2 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.84 (+0.11, -0.10) If the light curve continues to decay with a power-law decay index of 1.31, 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 4.4 x 10^-13 (4.8 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/01061223. This circular is an official product of the Swift-XRT team.