TITLE: GCN CIRCULAR NUMBER: 42401 SUBJECT: EP#01709247298: Swift-XRT counterpart detection DATE: 25/10/23 15:35:42 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 EP#01709247298, collecting 1.6 ks of Photon Counting (PC) mode data between T0+6.6 ks and T0+8.3 ks after the trigger. A likely counterpart has been found. This source is 43 arcmin from the position of the MAXI-detected transient GRB 251023B / MAXI J0451+122 (Kang et al., GCN Circ. 42392), well outside their error region, thus its association, while likely on temporal grounds, remains unconfirmed. The details of this source are: Source 1 (SWIFT J045400.4+123929): ================================== RA (J2000.0): 73.5018 = 04 54 00.43 Dec (J2000.0): +12.6583 = +12 39 29.9 Error: 3.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 22 arcsec from the Einstein Probe/WXT position. Mean rate: 0.152 +/- 0.011 ct s^-1 Mean flux: (5.94 +/- 0.44)e-12 erg cm^-2 s^-1 Peak rate: 0.221 +/- 0.049 ct s^-1 Peak flux: (8.6 +/- 1.9)e-12 erg cm^-2 s^-1 ECF: 3.91e-11 erg cm^-2 ct^-1 assuming NH=3.15e+21 cm^-2, gamma=1.97 determined from a spectral fit. XMM UL: 2.3e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 3.2-sigma above this 3-sigma upper limit. 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_FIELD00077. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42401. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...