GCN Circular 38918

J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini
(INAF-OAB), E. Ambrosi	(INAF-IASFPA) , M. A. Williams (PSU), S.
Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P.
Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on
behalf of the Swift-XRT team:

Swift-XRT has conducted further observations of the field of the
SVOM/ECLAIRs-detected burst GRB 250106A. The observations now extend
from T0+20.2 ks to T0+579.8 ks and have a total exposure time of 7.9
ks.  

Of the sources previously reported, "Source 1" is fading with >3-sigma
significance, and is therefore likely the GRB afterglow. Using 2981 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 = 117.23873, +63.81242 which is equivalent
to:

RA (J2000): 07h 48m 57.29s
Dec(J2000): +63d 48' 44.7"

with an uncertainty of 3.0 arcsec (radius, 90% confidence). This
position is 3.4 arcmin from the SVOM/ECLAIRs position.	The source is
fading with alpha >0.6.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.4 (+0.8, -0.7). The
best-fitting absorption column is  3.7 (+3.4, -2.4) x 10^21 cm^-2, in
excess of the Galactic value of 4.5 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 3.1 x 10^-11 (6.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.7 (+3.4, -2.4) x 10^21 cm^-2
Galactic foreground: 4.5 x 10^20 cm^-2
Excess significance: 2.2 sigma
Photon index:	     2.4 (+0.8, -0.7)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021753.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021753.

This circular is an official product of the Swift-XRT team.