GCN Circular 42284
Subject
GRB 251014D: Swift-XRT afterglow detection
Event
Date
2025-10-15T10:20:16Z (a day 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), S. Campana
(INAF-OAB), A. Melandri (INAF-OAR), T. Sbarrato (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:
Swift-XRT has performed follow-up observations of GRB 251014D. We
searched for X-ray sources in 2.9 ks of Photon Counting (PC) mode
data. The total exposure at the position of the afterglow (see below)
is 5.0 ks, obtained between T0+159.4 s and T0+22.3 ks.
An uncatalogued X-ray source is detected within the estimated 3-sigma
Swift-BAT error region (296 arcsec) and is fading with >3-sigma
significance, and is therefore likely the GRB afterglow. Using 1351 s
of PC mode data and 3 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 = 323.92080, -41.85533 which is equivalent to:
RA (J2000): 21h 35m 40.99s
Dec(J2000): -41d 51' 19.2"
with an uncertainty of 3.4 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.71 (+0.12, -0.11).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.64 (+/-0.06). The
best-fitting absorption column is 9.7 (+1.9, -1.8) x 10^20 cm^-2, in
excess of 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 4.1 x 10^-11 (4.6 x 10^-11) erg
cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
Total column: 9.7 (+1.9, -1.8) x 10^20 cm^-2
Galactic foreground: 2.1 x 10^20 cm^-2
Excess significance: 6.8 sigma
Photon index: 1.64 (+/-0.06)
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01404126.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/01404126.
This circular is an official product of the Swift-XRT team.