TITLE: GCN CIRCULAR NUMBER: 36332 SUBJECT: LIGO/Virgo S240422ed: Swift XRT observation of EP240426a DATE: 24/04/27 08:41:47 GMT FROM: K.L. Page at U Leicester <klp5@leicester.ac.uk> K.L. Page (U. Leicester), P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (U. Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB), J.J. Delaunay (PSU), M. De Pasquale (University of Messina), S. Dichiara (PSU), P. D’Avanzo (INAF-OAB), A. D’Aì (INAF-IASFPA) , V. D’Elia (ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson University), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S. Laha (NASA/GSFC), S.R. Oates (U. Birmingham), J.P. Osborne (U. Leicester), P. O’Brien (U. Leicester), M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (U Tor Vergata, INAF) report on behalf of the Swift team: Swift has conducted a follow-up observation of the candidate counterpart EP240426a (GCN Circ. 36313), starting 28.8 ks after the EP-FXT discovery. We detect an X-ray source 6.2" from, and thus consistent with, the localisation reported by EP-FXT: Source S240422ed_X255 ===================== RA: 121.85742 ( = 08h 07m 25.78s) J2000 Dec: -29.4593 ( = -29° 27′ 33.5″) J2000 Error: 5.3 (arcsec, radius, 90% confidence) Peak Rate: 0.012 +/- 0.003 ct s^-1 (0.3-10 keV) Peak Flux: 5.1e-13 +/- 1.3e-13 erg cm^-2 s^-1 RASS UL: 0.034 ct s^-1 (converted to XRT; 0.3-10 keV) so the source is not above the RASS 3-sigma upper limit For the flux conversions and comparisons with catalogues and upper limits from other missions given above, we assumed a power-law spectrum with NH=3x10^20 cm^-2, and photon index (Gamma)=1.7. However, for direct comparison with the flux of 9.2 x 10 ^-13 erg cm^-2 s^-1 given in GCN Circ. 36313, we estimate a value of 7.0 x 10^-13 erg cm^-2 s^-1, calculated over 0.5-10 keV, using Gamma = 2.0, corrected for the higher Galactic absorption of 4.3x10^21 cm^-2 in this direction. The results of the XRT automated analysis, including details of the sources detected during the follow-up of S240422ed, are online at https://www.swift.ac.uk/LVC/S240422ed/ This circular is an official product of the Swift XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/36332. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...