TITLE: GCN CIRCULAR NUMBER: 39056 SUBJECT: GRB 250127A: Swift-XRT observations DATE: 25/01/28 16:28:52 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk

J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected burst GRB 250127A, collecting 2.9 ks of Photon Counting (PC) mode data between T0+18.3 ks and T0+25.4 ks.

One uncatalogued X-ray sources have been detected within the estimated 90% SVOM/ECLAIRs error region (4.8 arcmin; GCN Circ. 39041), it is below the RASS limit and shows no definitive signs of fading in the two snapshot of observations that were taken. Details of this source are given below:

Source 2: RA (J2000.0): 169.6282 = 11:18:30.76 Dec (J2000.0): +3.3518 = +03:21:06.4 Error: 8.6 arcsec (radius, 90% conf.) Count-rate: (2.9 [+1.5, -1.1])e-3 ct s^-1 Distance: 138 arcsec from SVOM/ECLAIRs position. Flux: (3.3 [+1.7, -1.3])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

The source was also detected by the FXT telescope on board of Einstein Probe (GCN Circ. 39053), which observed this field around the same time of the XRT observations.

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/ToO_GRBs/00021757.

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

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