GCN Circular 41290

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

We have analysed 4.6 ks of XRT data for GRB 250807A, from 93 s to 91.2
ks after the   trigger. The data comprise 1.2 ks in Windowed Timing
(WT) mode (the first 5 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+6.7 ks) can be modelled with a
power-law decay with a decay index of alpha=1.75 (+0.11, -0.10).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.96 (+/-0.03). The
best-fitting absorption column is  1.90 (+/-0.11) x 10^21 cm^-2, in
excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.85 (+0.11, -0.10)
and a best-fitting absorption column of 1.8 (+0.4, -0.3) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.9 x 10^-11 (4.9 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.8 (+0.4, -0.3) x 10^21 cm^-2
Galactic foreground: 1.4 x 10^20 cm^-2
Excess significance: 8.0 sigma
Photon index:	     1.85 (+0.11, -0.10)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01340514.

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