TITLE: GCN CIRCULAR NUMBER: 29560 SUBJECT: GRB 210222B: Swift-XRT refined Analysis DATE: 21/02/23 19:23:17 GMT FROM: Phil Evans at U of Leicester K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), P.A. Evans (U. Leicester) and J.D. Gropp report on behalf of the Swift-XRT team: We have analysed 6.2 ks of XRT data for the Swift-BAT-detected burst GRB 210222B (Gropp et al. GCN Circ. 29545), from 111 s to 63.2 ks after the Swift-BAT trigger. The data are entirely in Photon Counting (PC) mode. Using 2754 s of PC mode data and 4 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 = 154.60574, -14.93170 which is equivalent to: RA (J2000): 10h 18m 25.38s Dec(J2000): -14d 55' 54.1" with an uncertainty of 1.4 arcsec (radius, 90% confidence). This position is 2.2 arcmin from the Swift-BAT position. The light curve can be modelled with an initial power-law decay with an index of alpha=0.19 (+/-0.16), followed by a break at T+827 s to an alpha of 1.30 (+0.12, -0.08). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.98 (+0.15, -0.14). The best-fitting absorption column is 1.4 (+0.5, -0.4) x 10^21 cm^-2, in excess of the Galactic value of 8.9 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 3.5 x 10^-11 (4.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.4 (+0.5, -0.4) x 10^21 cm^-2 Galactic foreground: 8.9 x 10^20 cm^-2 Excess significance: 1.9 sigma Photon index: 1.98 (+0.15, -0.14) If the light curve continues to decay with a power-law decay index of 1.30, the count rate at T+24 hours will be 3.1 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-13 (1.4 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/01034325. This circular is an official product of the Swift-XRT team.