TITLE: GCN CIRCULAR NUMBER: 41851 SUBJECT: GRB 250917B: Swift-XRT observations DATE: 25/09/17 17:14:55 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 5.5 ks of Photon Counting (PC) mode XRT data for GRB 250917B, collected between T0+142 s and T0+28.4 ks. Three uncatalogued X-ray sources have been detected within the estimated 3-sigma Swift-BAT error region (296 arcsec), however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below: Source 1: RA (J2000.0): 291.3458 = 19h 25m 23.00s Dec (J2000.0): +11.1151 = +11d 06' 54.5" Error: 5.5 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (5.5 [+1.3, -1.2])e-3 ct s^-1 Distance: 113 arcsec from Swift-BAT position. Flux: (1.26 [+0.30, -0.28])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 5: RA (J2000.0): 291.3929 = 19h 25m 34.30s Dec (J2000.0): +11.0748 = +11d 04' 29.2" Error: 7.7 arcsec (radius, 90% conf.) Count-rate: (4.6 [+5.4, -3.9])e-4 ct s^-1 Distance: 147 arcsec from Swift-BAT position. Source 6: RA (J2000.0): 291.4312 = 19h 25m 43.49s Dec (J2000.0): +11.1014 = +11d 06' 05.0" Error: 8.3 arcsec (radius, 90% conf.) Count-rate: (7.4 [+6.4, -4.8])e-4 ct s^-1 Distance: 192 arcsec from Swift-BAT position. Flux: (1.47 [+1.27, -0.95])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV) Three uncatalogued sources were also detected too far from the GRB position to be likely afterglow candidates. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/01350381. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41851. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...