TITLE: GCN CIRCULAR NUMBER: 30517 SUBJECT: GRB 210725A: Swift-XRT refined Analysis DATE: 21/07/26 00:09:08 GMT FROM: Phil Evans at U of Leicester M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and M.G. Bernardini report on behalf of the Swift-XRT team: We have analysed 6.3 ks of XRT data for GRB 210725A (Bernardini et al. GCN Circ. 30501), from 114 s to 64.8 ks after the BAT trigger. The data comprise 74 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. Using 1409 s of PC mode data and 2 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 = 215.37414, -1.19268 which is equivalent to: RA (J2000): 14h 21m 29.79s Dec(J2000): -01d 11' 33.6" with an uncertainty of 1.9 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.99 (+/-0.08). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.48 (+0.21, -0.19). The best-fitting absorption column is 8.0 (+6.8, -3.9) x 10^20 cm^-2, consistent with the Galactic value of 4.1 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 4.5 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.0 (+6.8, -3.9) x 10^20 cm^-2 Galactic foreground: 4.1 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.48 (+0.21, -0.19) If the light curve continues to decay with a power-law decay index of 1.99, the count rate at T+24 hours will be 1.2 x 10^-5 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.6 x 10^-16 (6.1 x 10^-16) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01061511. This circular is an official product of the Swift-XRT team.