TITLE: GCN CIRCULAR NUMBER: 31827 SUBJECT: GRB 220403B: Swift-XRT refined Analysis DATE: 22/04/04 07:08:18 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester) and N.J. Klingler report on behalf of the Swift-XRT team: We have analysed 6.3 ks of XRT data for GRB 220403B (Klingler et al. GCN Circ. 31820), from 86 s to 28.9 ks after the BAT trigger. The data comprise 50 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 refined XRT position is RA, Dec = 191.4734, +89.1846 which is equivalent to: RA (J2000): 12 45 53.62 Dec(J2000): +89 11 04.6 with an uncertainty of 3.5 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=4.4 (+/-0.4), followed by a break at T+229 s to an alpha of 0.35 (+0.04, -0.05). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.86 (+0.16, -0.14). The best-fitting absorption column is 1.47 (+0.51, -0.27) x 10^21 cm^-2, consistent with the Galactic value of 1.2 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7 x 10^-11 (4.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.47 (+0.51, -0.27) x 10^21 cm^-2 Galactic foreground: 1.2 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.86 (+0.16, -0.14) If the light curve continues to decay with a power-law decay index of 0.35, the count rate at T+24 hours will be 0.057 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.1 x 10^-12 (2.6 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01101053. This circular is an official product of the Swift-XRT team.