TITLE: GCN CIRCULAR NUMBER: 41644 SUBJECT: EP250901a: Swift-XRT observations DATE: 25/09/01 22:18:32 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 EP250901a, collecting 2.0 ks of Photon Counting (PC) mode data between T0+6.2 ks and T0+12 ks after the trigger. We have detected 1 source. This has been automatically classified as an known X-ray source. Known X-ray sources ------------------- Source 1 (SWIFT J181210.9+184216): ================================== RA (J2000.0): 273.0457 = 18 12 10.97 Dec (J2000.0): +18.7047 = +18 42 16.9 Error: 5.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 2.1 arcmin from the Einstein Probe/WXT position. Mean rate: 0.0570 +/- 0.0097 ct s^-1 Mean flux: (2.06 +/- 0.35)e-12 erg cm^-2 s^-1 Peak rate: 0.061 +/- 0.015 ct s^-1 Peak flux: (2.21 +/- 0.54)e-12 erg cm^-2 s^-1 ECF: 3.62e-11 erg cm^-2 ct^-1 assuming NH=4.95e+21 cm^-2, gamma=2.27 determined from a spectral fit. This matches a catalogued X-ray source 1RXS J181210.7+184228 in the ROSAT/RASSFSC catalogue. Details: Separation: 12.4" from the XRT source Cat Rate: 2.0e-02 +/- 8.7e-03 ct s^-1 Cat Flux: 6.7e-13 +/- 2.8e-13 erg cm^-2 s^-1 (0.3-10 keV) so the source is 2.5-sigma above the catalogued flux. The source may be fading, at the 0.9-sigma level. A SIMBAD object `1RXS J181210.7+184228' is 12.4" away. There are 3 2MASS objects 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. 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_FIELD00067. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41644. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...