GCN Circular 41862
Subject
GRB 250916A: Swift-XRT observations
Event
Date
2025-09-18T07:58:29Z (4 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Salvaggio
(INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows
(PSU), S. Lanava (PSU), S. Dichiara (PSU) and P.A. Evans (U. Leicester)
reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the
Fermi/GBM-detected burst GRB 250916A, collecting 1.6 ks of Photon
Counting (PC) mode data between T0+101.9 ks and T0+107.2 ks.
One uncatalogued X-ray source has been detected within the estimated
3-sigma GOTO error region (0.8 arcsec) given in GCN Circ. 41847, it is
below the RASS limit and shows no definitive signs of fading. However,
given its coincident location with the fading optical source, it is
indeed likely to be the afterglow. Details of this source are given
below:
Source 1:
RA (J2000.0): 26.5708 = 01h 46m 16.99s
Dec (J2000.0): +36.1652 = +36d 09' 54.6"
Error: 3.7 arcsec (radius, 90% conf. [Enhanced position])
Count-rate: 0.0274 +/- 0.0049 ct s^-1
Distance: 2 arcsec from GOTO position.
Flux: (9.2 +/- 1.6)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
An uncatalogued source was also detected, however this was too far from
the GRB position to be the afterglow.
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/00021859.
This circular is an official product of the Swift-XRT team.