TITLE: GCN CIRCULAR NUMBER: 42943 SUBJECT: GRB 251202A: Swift-XRT afterglow detection DATE: 25/12/02 11:00:16 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> B. Sbarufatti (INAF-OAB), S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 251202A. We searched for X-ray sources in 759 s of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 759 s, obtained between T0+2.4 ks and T0+24.0 ks. An uncatalogued X-ray source are clearly detected within the Einstein Probe/WXT error region. Using 411 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 = 122.11512, +40.61228 which is equivalent to: RA (J2000): 08h 08m 27.63s Dec(J2000): +40d 36' 44.2" with an uncertainty of 2.4 arcsec (radius, 90% confidence). This position is 10.3 arcsec from the EP/FXT position (Zhang et al., GCN Circ. 42937) and 2.2 arcsec from the optical counterpart reported by Li et al. (GCN 42934). The light curve can be modelled with a power-law decay with a decay index of alpha=1.08 (+0.33, -0.24). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.93 (+0.45, -0.22). The best-fitting absorption column is consistent with the Galactic value of 6.5 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 3.4 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 6.5 x 10^20 cm^-2 Intrinsic column: 6 (+/-166) x 10^20 cm^-2 at z=2.785 Photon index: 1.93 (+0.45, -0.22) If the light curve continues to decay with a power-law decay index of 1.08, the count rate at T+24 hours will be 0.018 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x 10^-13 (7.2 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/03000226. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/EP/EP_FIELD00086. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42943. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...