GCN Circular 45850
Subject
GRB 261007A: Swift-XRT afterglow detection
Event
Date
2026-10-08T07:22:21Z (11 hours ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
K.L. Page (U. Leicester), S. Campana (INAF-OAB), A. Melandri
(INAF-OAR), T. Sbarrato (INAF-OAB), S. Dichiara (PSU), D.N. Burrows
(PSU), J.J. DeLaunay (PSU), A.P. Beardmore (U. Leicester) 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 261007A, also known as EP261007a (GCN
Circ. 45828). We searched for X-ray sources in 1.9 ks of Photon
Counting (PC) mode data. The total exposure at the position of the
afterglow (see below) is 1.9 ks, obtained between T0+38.5 ks and
T0+44.0 ks.
An uncatalogued X-ray source is detected and is above the RASS 3-sigma
upper limit at this position, and is therefore likely the GRB
afterglow. The position of this source is also consistent with the
optical counterpart initially discovered by KAIT (GCN Circ. 45825).
Using 1918 s of PC mode data and 2 UVOT images, we find an enhanced XRT
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 11.61403, -17.69197 which is
equivalent to:
RA (J2000): 00h 46m 27.37s
Dec(J2000): -17d 41' 31.1"
with an uncertainty of 2.7 arcsec (radius, 90% confidence). This
position is 2.4 arcmin from the SVOM/ECLAIRs position. The light curve
is currently consistent with a constant source of mean count rate
1.3e-01 ct/sec.
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.74 (+0.29, -0.21). The
best-fitting absorption column is 3.7 (+7.0, -1.6) x 10^20 cm^-2,
consistent with the Galactic value of 2.1 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 3.7 x 10^-11 (4.0 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.7 (+7.0, -1.6) x 10^20 cm^-2
Galactic foreground: 2.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.74 (+0.29, -0.21)
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/00021917.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021917.
This circular is an official product of the Swift-XRT team.