GCN Circular 41010

R. Brivio (INAF-OAB), D.N. Burrows (PSU), M.A. Williams (PSU), S.
Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB) and P.A. Evans report on
behalf of the Swift-XRT team:

We have analysed 5.7 ks of XRT data for GRB 250706A, from 131 s to 55.6
ks after the   trigger. The data comprise 285 s in Windowed Timing (WT)
mode (the first 10 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. The refined XRT position is RA,
Dec = 284.0176, +32.3216 which is equivalent to:

RA (J2000): 18 56 04.22
Dec(J2000): +32 19 17.6

with an uncertainty of 3.5 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.76 (+0.12, -0.13), followed by a break at T+427 s to
an alpha of 2.27 (+0.18, -0.14).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.87 (+/-0.09). The
best-fitting absorption column is  2.6 (+/-0.4) x 10^21 cm^-2, in
excess of the Galactic value of 1.2 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.8 x 10^-11 (5.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     2.6 (+/-0.4) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^21 cm^-2
Excess significance: 6.4 sigma
Photon index:	     1.87 (+/-0.09)

If the light curve continues to decay with a power-law decay index of
2.27, the count rate at T+24 hours will be 3.3 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.3 x
10^-15 (1.7 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01330958.

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