GCN Circular 40705

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

We have analysed 5.0 ks of XRT data for GRB 250610B, from 2.9 ks to
105.7 ks after the  SVOM/ECLAIRs trigger. The data are entirely in
Photon Counting (PC) mode. Using 2013 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 =
200.17991, +31.10477 which is equivalent to:

RA (J2000): 13h 20m 43.18s
Dec(J2000): +31d 06' 17.2"

with an uncertainty of 2.8 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.68 (+0.12, -0.10).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.86 (+0.33, -0.25). The
best-fitting absorption column is  3.1 (+7.7, -2.0) x 10^20 cm^-2,
consistent with the Galactic value of 1.1 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 3.5 x 10^-11 (3.7 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.1 (+7.7, -2.0) x 10^20 cm^-2
Galactic foreground: 1.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.86 (+0.33, -0.25)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019863.

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