TITLE: GCN CIRCULAR NUMBER: 41699 SUBJECT: GRB 250903A: Swift-XRT observations DATE: 25/09/04 13:38:46 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 250903A, collecting 2.4 ks of Photon Counting (PC) mode data between T0+12 ks and T0+24 ks after the trigger. We have detected 2 sources inside the ECLAIRs error region. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J234712.1-755757): ================================== RA (J2000.0): 356.8008 = 23 47 12.19 Dec (J2000.0): -75.9660 = -75 57 57.6 Error: 4.3 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 2.7 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.0387 [+0.0049, -0.0047] ct s^-1 Mean flux: (1.33 [+0.17, -0.16])e-12 erg cm^-2 s^-1 Peak rate: 0.052 +/- 0.014 ct s^-1 Peak flux: (1.80 +/- 0.47)e-12 erg cm^-2 s^-1 ECF: 3.42e-11 erg cm^-2 ct^-1 assuming NH=4.68e+20 cm^-2, gamma=1.95 determined from a spectral fit. XMM UL: 2.0e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. The source may be fading, at the 0.8-sigma level. Source 2 (SWIFT J234819.4-755214): ================================== RA (J2000.0): 357.0812 = 23 48 19.49 Dec (J2000.0): -75.8707 = -75 52 14.5 Error: 6.4 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.8 arcmin from the SVOM/ECLAIRs position. Mean rate: (8.6 [+2.9, -2.4])e-3 ct s^-1 Mean flux: (1.06 [+0.36, -0.30])e-11 erg cm^-2 s^-1 Peak rate: (8.6 [+2.9, -2.4])e-3 ct s^-1 Peak flux: (1.06 [+0.36, -0.30])e-11 erg cm^-2 s^-1 ECF: 1.23e-09 erg cm^-2 ct^-1 assuming NH=4.41e+20 cm^-2, gamma=-2.35 determined from a spectral fit. XMM UL: 1.9e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 2.7-sigma above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `LEDA 242511' is 4.1" away. There is 1 2MASS object within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. Source 1 position is consistent with the optical counterpart discovered by TRT (GCN 41679). 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/SVOM/SVOM_FIELD00034. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41699. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...