GCN Circular 39681
Subject
GRB 250311A: Swift-XRT observations
Date
2025-03-12T09:58:00Z (2 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P.
Beardmore (U. Leicester), J.P. Osborne (U. Leicester), R. Brivio
(INAF-OAB), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR) and P.A.
Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 250311A/MAXI J1457-026 (GCN Circ. 39660) in a series of
observations tiled on the sky. The total exposure time is 1.4 ks,
distributed over 4 tiles; the maximum exposure at a single sky location
in the tiling was 731 s. The data were collected between T0+34.4 ks and
T0+36.0 ks, and are entirely in Photon Counting (PC) mode.
Two uncatalogued X-ray sources have been detected, however none of them
is above the RASS limit or shows definitive signs of fading. Therefore,
at the present time we cannot identify which, if any, is the afterglow.
Details of these sources are given below:
Source 1:
RA (J2000.0): 224.4476 = 14:57:47.43
Dec (J2000.0): -2.7859 = -02:47:09.2
Error: 9.8 arcsec (radius, 90% conf.)
Count-rate: (9.8 [+6.3, -4.5])e-3 ct s^-1
Distance: 777 arcsec from MAXI position.
Source 2:
RA (J2000.0): 224.4381 = 14:57:45.15
Dec (J2000.0): -2.7813 = -02:46:52.7
Error: 8.7 arcsec (radius, 90% conf.)
Count-rate: 0.0134 [+0.0074, -0.0055] ct s^-1
Distance: 744 arcsec from MAXI position.
We note that these observations do not cover the localisation of X-ray
transient EP250311a (GCN 39664), which may be associated with the same
trigger.
The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00135.
This circular is an official product of the Swift-XRT team.