TITLE: GCN CIRCULAR NUMBER: 41208 SUBJECT: GRB 250727A: Swift-XRT afterglow confirmation and refined analysis DATE: 25/07/31 05:57:17 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk

K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

We have analysed 5.9 ks of XRT data for GRB 250727A, from 2.4 ks to 300.7 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. During this second observation, source 1 (SWIFT J234539.1-811248) given in GCN Circ. 41180 is found to have faded at the 3.7-sigma level, so we believe this to be the X-ray afterglow. We also note that EP-FXT found this source to have faded (GCN Circ. 41199).

Using 1353 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 356.41475, -81.21390 which is equivalent to:

RA (J2000): 23h 45m 39.54s Dec(J2000): -81d 12' 50.1"

with an uncertainty of 4.3 arcsec (radius, 90% confidence). The source is fading with alpha >0.3.

The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019965.

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

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