TITLE: GCN CIRCULAR NUMBER: 41624 SUBJECT: EP250831a: Swift-XRT observations DATE: 25/09/01 04:39:35 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 EP250831a, collecting 1.8 ks of Photon Counting (PC) mode data between T0+24 ks and T0+30 ks after the trigger. We have detected 1 source 4.6 arcmin from the WXT position, somewhat outside the 90% error region of 2.9 arcmin (GCN 41619). This has been automatically classified as an uncatalogued X-ray source.

Uncatalogued X-ray sources --------------------------

Source 1 (SWIFT J025130.9-360728): ================================== RA (J2000.0): 42.8789 = 02 51 30.94 Dec (J2000.0): -36.1245 = -36 07 28.2 Error: 5.0 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.6 arcmin from the Einstein Probe/WXT position. Mean rate: (7.6 [+2.8, -2.3])e-3 ct s^-1 Mean flux: (1.97 [+0.73, -0.59])e-13 erg cm^-2 s^-1 Peak rate: (7.6 [+2.8, -2.3])e-3 ct s^-1 Peak flux: (1.97 [+0.73, -0.59])e-13 erg cm^-2 s^-1 ECF: 2.58e-11 erg cm^-2 ct^-1 assuming NH=3.05e+20 cm^-2, gamma=2.54 determined from a spectral fit. LSXPS UL: 1.7e-02 ct/sec, (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.

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_FIELD00066.

This circular is an official product of the Swift-XRT team.

View this GCN Circular online at https://gcn.nasa.gov/circulars/41624. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...