TITLE: GCN CIRCULAR NUMBER: 42908 SUBJECT: EP251130a: Swift-XRT counterpart detection DATE: 25/11/30 19:00:56 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 EP251130a, collecting 2.0 ks of Photon Counting (PC) mode data between T0+5.8 ks and T0+11 ks after the trigger. A likely counterpart has been found. The details of this source are: Source 1 (SWIFT J064404.8+272302): ================================== RA (J2000.0): 101.0203 = 06 44 04.87 Dec (J2000.0): +27.3839 = +27 23 02.0 Error: 3.9 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 75 arcsec from the Einstein Probe/WXT position. Mean rate: 0.0618 [+0.0070, -0.0068] ct s^-1 Mean flux: (2.21 [+0.25, -0.24])e-12 erg cm^-2 s^-1 Peak rate: 0.139 +/- 0.031 ct s^-1 Peak flux: (5.0 +/- 1.1)e-12 erg cm^-2 s^-1 ECF: 3.57e-11 erg cm^-2 ct^-1 assuming NH=1.80e+21 cm^-2, gamma=1.97 determined from a spectral fit. XMM UL: 3.5e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 1.4-sigma above this 3-sigma upper limit. The source may be fading, at the 2.6-sigma level. This position is consistent with the candidate optical counterpart reported by COLIBRI (GCN 42904). 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_FIELD00085. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42908. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...