GCN Circular 41208
Subject
GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
Event
Date
2025-07-31T05:57:17Z (19 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
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.