GCN Circular 42162

V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio
(INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU),
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 6.5 ks of XRT data for GRB 251007A, from 58 s to 39.2
ks after the   trigger. The data comprise 362 s in Windowed Timing (WT)
mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+11.9 ks) can be modelled with a
power-law decay with a decay index of alpha=1.46 (+/-0.13).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.92 (+/-0.04). The
best-fitting absorption column is  1.79 (+0.15, -0.14) x 10^21 cm^-2,
in excess of the Galactic value of 4.0 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.82 (+/-0.12) and a
best-fitting absorption column of 1.6 (+/-0.4) 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:	     1.6 (+/-0.4) x 10^21 cm^-2
Galactic foreground: 4.0 x 10^20 cm^-2
Excess significance: 5.1 sigma
Photon index:	     1.82 (+/-0.12)

If the light curve continues to decay with a power-law decay index of
1.46, the count rate at T+24 hours will be 0.052 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.0 x
10^-12 (2.5 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01402466.

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