TITLE: GCN CIRCULAR NUMBER: 41802 SUBJECT: EP250911a: Swift-XRT observations DATE: 25/09/11 17:36:52 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 Einstein Probe/WXT-detected source EP250911a (Liang et al., GCN Circ 41788), collecting 1.7 ks of Photon Counting (PC) mode data between T0+5.5 ks and T0+11 ks after the trigger. We have detected 1 source consistent with the EP/FXT position (Liang et al., GCN Circ 41788). This has been automatically classified as an uncatalogued X-ray source. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J235004.5+291757): ================================== RA (J2000.0): 357.5191 = 23 50 04.58 Dec (J2000.0): +29.2992 = +29 17 57.1 Error: 4.6 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 62 arcsec from the Einstein Probe/WXT position. Mean rate: 0.0239 +/- 0.0047 ct s^-1 Mean flux: (8.3 +/- 1.6)e-13 erg cm^-2 s^-1 Peak rate: 0.0239 +/- 0.0047 ct s^-1 Peak flux: (8.3 +/- 1.6)e-13 erg cm^-2 s^-1 ECF: 3.47e-11 erg cm^-2 ct^-1 assuming NH=5.84e+20 cm^-2, gamma=1.92 determined from a spectral fit. XMM UL: 7.6e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. 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. We note that source 1 also matches the position of the optical counterpart to EP250911a reported by Quirola-Vasquez et al. (GCN Circ. 41790) and Angulo et al. (GCN Circ. 41793). 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/EP/EP_FIELD00073. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41802. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...