TITLE: GCN CIRCULAR NUMBER: 42084 SUBJECT: GRB 251002A: Swift-XRT afterglow detection DATE: 25/10/03 10:06:49 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA), S. Lanava (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 251002A. We searched for X-ray sources in 1.5 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 1.5 ks, obtained between T0+3.6 ks and T0+9.2 ks. Three uncatalogued X-ray sources are detected within the estimated 3-sigma SVOM/ECLAIRs error region (392 arcsec), of which one ("Source 1") is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 1503 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 = 13.90813, -5.56678 which is equivalent to: RA (J2000): 00h 55m 37.95s Dec(J2000): -05d 34' 00.4" with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position is consistent with the optical candidate (Palmerio et al. GCN 42061) and the EP-FXT X-ray candidate (Sun et al. GCN 24075). The light curve can be modelled with a power-law decay with a decay index of alpha=1.27 (+0.28, -0.25). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.62 (+0.20, -0.18). The best-fitting absorption column is 8.3 (+6.5, -2.8) x 10^20 cm^-2, consistent with the Galactic value of 5.5 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 4.2 x 10^-11 (4.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.3 (+6.5, -2.8) x 10^20 cm^-2 Galactic foreground: 5.5 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.62 (+0.20, -0.18) If the light curve continues to decay with a power-law decay index of 1.27, the count rate at T+24 hours will be 0.014 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.9 x 10^-13 (6.5 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/03000125. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00039. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42084. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...