TITLE: GCN CIRCULAR NUMBER: 33365 SUBJECT: GRB 230217A: Swift-XRT afterglow detection DATE: 23/02/22 08:59:54 GMT FROM: Phil Evans at U of Leicester M. Capalbi (INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has conducted further observations of the field of the Swift-BAT-detected burst GRB 230217A (Barthelmy et al. GCN Circ. 33363). The observations now extend from T0+45.9 ks to T0+342.9 ks. Of the sources reported by Capalbi et al. (GCN Circ. 33348), "Source 3" is fading with >3-sigma significance, and is therefore likely the GRB afterglow. Using 874 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 280.77002, -28.83740 which is equivalent to: RA (J2000): 18h 43m 04.80s Dec(J2000): -28d 50' 14.6" with an uncertainty of 4.7 arcsec (radius, 90% confidence). This position is 67 arcsec from the Swift-BAT position. The light curve can be modelled with a power-law decay with a decay index of alpha=1.1 (+0.6, -0.4). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.6 (+0.8, -0.4). The best-fitting absorption column is consistent with the Galactic value of 1.6 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 4.4 x 10^-11 (5.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.6 (+/-4.1) x 10^21 cm^-2 Galactic foreground: 1.6 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.6 (+0.8, -0.4) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01154967. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/01154967. This circular is an official product of the Swift-XRT team.